The War on Salt
This week we delve into the science of salt: what does it do in the body, how can it cause problems for farmers, and what avenues are scientists exploring to desalinate sea water and keep us all refreshed? Plus, one in ten adults have ADHD, the contagious cancer that's followed dogs across the world, and how scientists are growing a brain in a dish to find answers to Alzheimer's Disease...
In this episode
00:56 - ADHD can begin in adulthood
ADHD can begin in adulthood
with Jessica Agnew-Blais, King’s College London
Do you struggle to concentrate on tasks, and frequently feel "unsettled"? If so, you might be one of the nearly 10% of the adult population with ADHD - attention deficit hyperactivity disorder. Previously we thought that this was mainly a childhood condition but now a new study, by King's College London's Jessica Agnew-Blais, suggests that a large number of individuals develop the condition in adulthood, despite not showing any signs of it as youngsters...
Jessica - We assessed people for ADHD in young adulthood, so age 18, and then we looked back at ADHD assessments done in childhood at ages 5, 7, 10 and 12 and we found that, actually, nearly 70% of people who had ADHD at 18 did not have ADHD at any of these childhood assessments.
Chris - Goodness! So that means those individuals did not receive a diagnosis when they were little, so are these new adult cases of ADHD?
Jessica - Right, exactly. And, even over and above that, not only did they did not receive diagnosis but we actually asked their their mothers and their teachers about their ADHD symptoms in childhood, when they were 5, 7, 10, and 12, and it seems that these individuals did not have the disorder at any of these ages in childhood.
Chris - Do you think it's the same condition then?
Jessica - That's a very good question and is really one of the main questions that our study raises. I think a lot further research needs to be done to understand this better and to know whether this late onset ADHD as the same kind of causes as ADHD that begins in childhood and if would respond similarly to the same kind of treatments, for example.
Chris - Well, I'm thinking, obviously, when one is in the childhood time of one's life, it's a very different environment; very supportive, fewer risks, lower stress than when someone is a young adult who might be going off to university for the first time or in the workplace for the first time. So the demands on that individual and the support network can be quite different and so, is it possible they still had the same risk it was just disclosed at a different time in their life?
Jessica - Yes, that's exactly right. There's one thing that we considered in our study is that perhaps these individuals would have had ADHD in childhood, but they were in such supportive family environments that the disorder was not apparent until they left home later on. So, one thing I thing would be really interesting is to follow up these individuals later in life. So, several years from now, are these people who had late onset ADHD and particular problems with ADHD when they were age 18, do they still have these problems once they've maybe adjusted a bit more to adult life?
Chris - Based on the numbers that you looked at with your twin study, what proportion of adults in the UK, or equivalent countries, might therefore have one of these adult diagnosis of ADHD?
Jessica - We found that, overall, there was about an 8% prevalence of adult ADHD at age 18 and that among these people nearly 70%, so 67.5%, did not have a childhood diagnosis of ADHD.
Chris - That's a lot of people, isn't it?
Jessica - Ahmm Ahmm.
Chris - What can we do about it?
Jessica - I think the first step is around recognition and so I think for clinicians especially, a lot of them are of the mindset and have been taught that if you were to have an ADHD diagnosis, you have to have it in childhood. So they may ask individuals parents about how they acted as children or they might even want to speak to someone's teachers to say, well were these problems with hyperactivity and inattention present in childhood? But here we found that for a lot of these people, they didn't really have particular problems with these symptoms when they were children so whether we really need to focus on looking back to that childhood period is not necessarily clear.
04:44 - Contagious cancer steals DNA from host
Contagious cancer steals DNA from host
with Andrea Strakova & Máire Ní Leathlobhair, The University of Cambridge
CTVT, or canine transmissible venereal tumour, is very unusual kind of cancer. The majority of cancers we see arise from an individual's own cells, but in this dog tumour the cells from that animal's cancer are infectious and they can spread to other dogs when the animals mate. Now scientists at Cambridge University have studied dogs with the cancer from around the world, turning up a big surprise: the cancers have adopted DNA from the host dogs they've infected. Specifically this has happened in structures inside cells called mitochondria, which provide cells with their energy and this is how the tumour keeps fit. Georgia Mills went to see researcher Andrea Strakova at Cambridge University's Department of Veterinary Medicine...
Andrea - We collected over 400 samples from 39 countries around the world and we looked at the mitochondrial DNA of these samples. So mitochondria are, let's say, batteries of the cell, which provide energy and they have a small piece of DNA which codes for the proteins needed by the mitochondria. And we looked at the mutations, or genetic changes in these mitochondrial DNA, which gave us a unique opportunity to look at the ways that the disease spreads around the world.
Georgia - Because these cancer cells are transferred directly from dog to dog, cells in each tumour are from the original dog to contracted it 11,000 years ago, meaning it can be traced back to that time. But, very occasionally throughout history, the tumour in a specific dog has done something a little usual and grabbed mitochondrial DNA from cells of the host dog.
Mora - My name is Máire Ní Leathlobhair and I'm a second year PhD student in the transmissible cancer group. If you can imagine that dogs usually carry around their own normal mitochondria, but these host mitochondria then swapped into the cancer cells and then these are spread throughout global dog populations over hundreds to thousands of years. And using these patterns we saw across global population of samples we were able to track how different groups of dogs afflicted with CTV moved.
Georgia - This snatching of DNA happened at least five times in history, meaning the team could get a clearer idea of the movement of infected dogs through time, and this pattern matched old trade routes across the ocean so it looks like people took their dogs with them to the high seas. Andrea...
Andrea - From the five different transfers of mitochondria, we were able to define five different clades, and the timing of the clades was based on the mutations we found in each of the mitochondria.
Georgia - By working out the normal background rate of mutations, you can look at these, you can take the DNA from the dogs that are infected, look at the DNA in the mitochondria and then find out how old this cancer is?
Andrea - Exactly, because we use the so called molecular clock. So we can look at the number of mutations, which we see in each of these different mitochondrial types, and that helps us to look at the timing when each of them arise.
Georgia - And then these different clades are from when these big events when mitochondrial DNA switched?
Andrea - Exactly. So these are from the time when the mitochondrial DNA from the dog actually jumped into the tumour cell, and this was the switch as you describe.
Georgia - Why would this happen?
Andrea - Well, we think that one of the reasons could be that the mitochondria in the tumour has so many mutations that they would be, in a way, less functional and therefore, gaining the mitochondria from the normal dog, that would provide a selective advantage for the cell.
Georgia - By grabbing this mitochondrial DNA from the healthy dogs they can reduce the amount of harmful genetic changes that will have built up over time. A very clever trick, but the team came across something even more surprising...
Andra - Well, we found one very, very, special case in a dog in Nicaragua. What actually happened in this dog is that not only did the mitochondria jump from the dog into the tumour cell but actually, we found that these two mitochondria mixed to create a single mitochondria, formed both by the tumour and the dog DNA.
Georgia - And why is this unusual?
Andrea - This is something that has never been reported in cancers before. We believe this could be because it may be very difficult to detect so we suspect this process could actually be a lot more common than expected, but we just don't have the tools to detect it. So what we are planning to do in the future is to look more widely to see if this type of mitochondrial mixing is found in other tumours around the world. And also, it would be very interesting to see if we can see this type of mixing in human cancers as well.
Georgia - Do you think this would have any implications for cancer treatment?
Andrea - If mitochondrial recombination is, indeed, common in human cancers as well, then certainly there would be a potential for targeted treatment.
10:16 - Myth: Bees shouldn't be able to fly
Myth: Bees shouldn't be able to fly
with Kat Arney, The Naked Scientists
Kat Arney was all of a buzz this week for her mythconception about the flight of the bumblebee...
Kat - We're finally moving towards sunnier days and the flowers are blooming. And where you get flowers, you get bees - but looking at a big, buzzing bumblebee making its way from bloom to bloom on tiny wings, you might wonder how on earth it stays airborne. You wouldn't be the only one - it's long been held that bumblebees shouldn't be able to fly, and it's been repeated by everyone from management consultants and marketeers to US presidential candidates. In 2008, wannabe president Mike Huckabee said "It's scientifically impossible for the bumblebee to fly; but the bumblebee, being unaware of these scientific facts, flies anyway."
So given that bees obviously can fly, travelling at a rate of 3 meters per second, are they wilfully defying all the proven laws of aerodynamics and science as we know them, or is there something else going on?
One mistake people make when thinking about the flight of the bumblebee is to assume that there are similarities with other winged things, such as birds or aeroplanes. In fact, this is probably where the myth arose, based on calculations of the aerodynamic properties of typical wings from decades ago suggesting that the bumblebee's wings are too small to lift its weight into the air. But bees are not birds, and they're built very differently. And simplistic models that assume their wings are rigid like an aeroplane and work in the same way are bound to be wrong.
Rather than being built for life on the wing, soaring freely through the air, bumblebees are the tanker trucks of the insect world, evolved to carry huge loads of pollen back to their hive. To figure out exactly how their wings move to propel them through the air, back in 2009 Oxford University scientists put bumblebees in a wind tunnel with some smoke and high-speed cameras. And although the bees clearly do fly, they do it in an unusual way- unlike most flying animals their left and right wings flap independently and the airflow around them never joins up to help them slip through the air more easily. It's described best as a 'brute force' approach to flying, rather than the elegant soaring of a bird or the streamlined flight of a fly.
What's more, a bee's wings are much more flexible than the more rigid feathered wings of a bird. By wiggling and rotating their wings around hundreds of times per second, the bees create what are known as vortices - or to put it simply, mini-hurricanes - that give them the lift they need to say aloft. This is much more similar to the whirring blades of a helicopter rather than the fixed wings of a plane, and nobody goes around saying that helicopters shouldn't be able to fly.
So - although they may do it in an unorthodox manner, the flight of the bumblebee doesn't defy physics. In fact, this myth is often used as a way of being disparaging about science - implying that if something doesn't fit into our current models or we don't know how it happens then science is somehow at fault or that there a mystical forces at work. Of course, as this story shows, when something appears to defy the laws of physics, it's because we haven't found the right way of studying it. So next time you hear someone repeat this myth, tell them to buzz off!
13:49 - Growing an Alzheimer's brain in a dish
Growing an Alzheimer's brain in a dish
with Rosa Sancho, Alzheimer’s Research UK & Rick Livesey, Cambridge University
In recent years, large numbers of articles have been published about advances in the fight against dementia - the loss of a person's mental faculties which often accompanies old age. But how much further forward are we not only in treating but also in diagnosing and understanding dementia? Graihagh Jackson met with Rosa Sancho, head of research at Alzheimer's Research UK...
Rosa - Alzheimer's disease is a form of dementia; it is the most common cause of dementia, and there's a hallmark to all of these diseases which is an accumulation of proteins in the brain. So, in the case of Alzheimer's disease, there's an accumulation of two proteins (amyloid and tau). Amyloid forms sticky clumps in the brain outside the brain cells, called plaque, and tau forms tangles inside the cells.
Graihagh - And we have no idea why these proteins build up?
Rosa - We don't know really what causes these diseases. It's likely to be a mix of genes and environment but recent research advances have told us a lot about these causes.
Graihagh - And one bit of research that has told us a lot more about the workings of Alzheimer's on a neuron by neuron basis is done by Dr. Rick Livesey at Cambridge University. What's he been doing that's so remarkable? Well, he's growing brains from skin cells in a petri dish.
Rick - So here in the lab, what we've been doing is making human nerve cells from people with different types of dementia, including Alzheimer's disease, and that allows us to study how the disease starts and progresses within real human nerve cells, but within a lab situation.
Graihagh - Rick calls them nerve cells, but these nerve cells or neurons are the building blocks of our brain. But how can you get a brain to grow in a lab... Well he's basically made a womb.
Rick - What these big cabinets are is essentially they're at body temperature, so they keep the stem cells happy and, actually, what they're doing is they're growing in a mixture of salt and sugar and it's like they're in normal body fluids. So, if we take them out and show you on the microscope...
Graihagh - They are literally petri dishes with some fluid swishing around. They actually look pretty unremarkable, that is until you put them under a microscope and then you can see all these neurons. But how do you get these brain cells in the first instance? It all starts with skin cells which they reverse engineer into a stem cell. These are a bit like the first few cells that then form an embryo and can, basically, turn into any other type of cell. They could form a bit of your bone, or you lung, or your eye, but Rick makes them turn into brain cells.
Rick - In normal development, a single cell ends up making an entire body or an organism. And we understand a fair amount about how cells talk to one another and the genetic mechanisms by which that happens so we use that knowledge to, essentially, drive the stem cell down a particular road and ignore others.
Graihagh - Now I assume you're not growing entire brains in petri dishes here, only a region of the brain?
Rick - Yes. So we grow this thing called the cerebral cortex and only a small part of it. To put it in context, a human brain weighs about 1.5 kilogram - that's an awful lot of cells. It's the order of 100 billion cells. So we typically will grow a couple of million cells at a time.
Graihagh - I find that kind of amazing and slightly weird.
Rick - Well, you know, biological systems have a lot of self-organising properties, so the neurons we're showing you now are organised largely in two dimensions.
Graihagh - Because what we're seeing here is... well it doesn't resemble a brain at all. You have to put it under a microscope to be able to even see it. Why do you need to do this - how does this help?
Rick - Most people, when they hear about Alzheimer's, what they're used to hearing about is these MRIs which show really small brains. That's very late in the disease. The early stage of the disease is characterised by what's called "myocognitive impairment," where people get the memory loss and what's actually underlying that is it's a dysfunction with how neurons communicate with one another. And how neurons communicate with one another is these things called "synapses," which is the gap between each individual nerve cells. And, as far as we can tell, all the early symptoms of the disease are what we would call a manifestation of synaptic dysfunction and that's why it's so important to be looking at real neurons in the lab because that's the level at which the disease really operates.
Graihagh - Now that you can see how this disease progresses on this tiny, tiny scale, how does that then become an application outside the lab?
Rick - It allows us to study the mechanisms by which the disease starts to progress. And that means we understand it more and the jargon we use is the biological pathways, and biological pathways are the level at which you target drugs.
Graihagh - Because my understanding is, currently, a lot of the drugs for Alzheimer's tend to be more treating the symptoms than the actual progression of the disease.
Rick - Yes. I mean there are no disease modifying drugs for Alzheimer's disease. Like many people I get emails most weeks from families when a family member is diagnosed just asking what's available, what are the trials? And it's very common when I reply and say "well actually there are no drugs which will halt the disease or slow the disease," a very common response I get back is "are you kidding me." Because most people just happily up till then have been unaware of the fact that it's not like cardiovascular disease, it's not like cancer, we really have very little in our toolkit.
Graihagh - I do find this quite shocking because, as a journalist, I'm always leafing through press releases and it feels as though every week there's some sort of Alzheimer's advance. I put this to Rosa...
Rosa - You're right. What you're seeing is a huge momentum behind dementia research. There is political will, there is more funding meaning that there are more discoveries being made, more clinical trials ongoing than ever before, and new ways of treating the disease, which really weren't here before.
Graihagh - I wonder whether you could give us a quick 'pit stop' tour of what you think has been really important in advancing our understanding of the disease?
Rosa - Genetic studies have shown us new avenues of research. We also have more knowledge now of how amyloid and tau interact to cause brain cell death. These have led to exciting new treatments that are anti-amyloid and anti-tau therapies as well as diagnostic markers to try to trace these two proteins in the
20:40 - Tsunamis on Mars
Tsunamis on Mars
with David Rothery, Open University
Was Mars once a surfer's paradise? Possibly, if you like surfing on tsunamis! We know thanks to a succession of probes that there are strong signatures of water sitting beneath the surface of the red planet, and researchers have concluded that Mars was once dominated by a massive ocean. But if the ocean was there, where's the shoreline that it once lapped up against? It's only with an eye of faith that something fitting the bill can just about be seen on satellite images of the surface. Well now an international team of scientists think they know the answer. There was a shoreline, but some giant waves triggered by two massive meteor impacts washed it away... Planetary scientist David Rothery, who wasn't involved with the study, has been taking a look at the data for Chris Smith...
David - So what's been suggested is that the shoreline of the now vanished ocean has been washed over by tsunami waves. In one particular part of the shoreline, the team that's produced this new paper, have shown two deposits that have washed up over where the shoreline would have been depositing boulders at a high level and then have washed back carving backwash channels. So we've got evidence of waves dumping stuff ashore and then the water draining back into the ocean from two tsunamis and these would have been generated by large meteorites, small asteroids, crashing into the ocean creating the tsunami.
Chris - And how big would those tsunamis have been?
David - Well, they're taking about 30 kilometer size craters. It kind of depends whether the ocean was ice covered or free water at the surface how big the waves would be but once they reach shallow water at the edge of the ocean and rush on shore, they do ramp up. So we're looking at waves in the order of 10 metres high running ashore and running uphill for several tens of metres under their own momentum carrying boulders with them and then draining back into the sea carving these channels.
Chris - What's the backstory to all of this? We have evidence that Mars was once a very wet place so why is the whole idea of their being an ocean there contentious?
David - Well, you're right Chris. There's plenty of evidence that Mars has been wet in the distant past. There's some very big channel systems draining through the high standing southern hemisphere of the planet into the low northern hemisphere. The northern hemisphere is low lying and covered in sediments. There may be some ice mixed in with those sediments still today and that is where the ocean would have been 3 or 3½ billion years ago. It's now long since dried out and/or frozen into the sediments on the bottom but plenty of signs that there was an ocean there once upon a time.
Now the shoreline of this ocean has been hard to locate. You can trace it if you try and it's not an obvious shoreline and perhaps now it's been suggested that there have been tsunamis washing up and down across this shoreline, that's why the usual shoreline markers aren't so obvious to see because they've been obliterated by the occasional series of tsunami waves rushing ashore and then draining back down into the ocean basin.
Chris - How have the team who've come up with these predictions actually done this?
David - Well, they've been using a variety of images from spacecraft orbiting Mars, including some images with really fine spatial resolution. I'm looking here at a picture that's showing angular boulders just a few metres in size in a big deposit above the shoreline that they say have been washed uphill from the sea by the waves crashing ashore. So, it's a variety of high resolution and medium resolution images and they've traced the shorelines for over 1,000 kilometers.
Chris - Right, so they've starting with what we do know, which is we can see what we can see. We've got very good images of the surface of Mars and they're asking what could have produced these images, and so they've backwards extrapolating what could have done that?
David - That's right. I mean, I wish I'd thought of this because it's pretty obvious that on a planet like Mars, if you've got a sea, doesn't have much atmosphere to slow anything down and we do know in the distant past there were craters forming on Mars. There would have been a dozen or so 30 kilometer craters formed on the northern hemisphere of Mars during the time when this ocean was supposed to have been there. So it's pretty obvious that impacts into that ocean ought to have caused tsunami waves. It happened in the Earth in the distant past as well. And these guys have found the deposits and the erosional features of the kind that would be produced by tsunami waves crashing ashore and that helps explain why the more conventional shoreline features are harder to see because in many places they've been obliterated by the effects of these very rare tsunamis, so it hangs together. It's a seductive story. I'm not sure everybody's going to believe it straight away but it's one of these damned good ideas that you think with hindsight... yes, that works.
26:28 - Salt of the Earth
Salt of the Earth
with Professor Chris Jackson, Imperial College London
Salt might be something we associate with fish and chips, but once it was one of the world's most valuable resources, allowing armies to conquer and civilisations to thrive. To find out more about salt and how has it shaped our history Georgia Mills spoke to Imperial College London's Earth scientist, Chris Jackson.
Chris - Salt actually spans quite a broad range of rock types. Essentially one of the common physical properties of these types of minerals is that they can be dissolved in water and then when the water is evaporated off, these minerals precipitate out. So, imagine taking a pan full of water and putting lots of salt in it and then boiling that pan for an hour or two hours, all of the steam will be rising off, so that's all the water turning into steam. And then at the end of that experiment you'll be left with a film of the material that can't be kept within the vapour and is actually left as a solid in the base of that pan. So that's what we mean by evaporite and precipitation.
Georgia - While salt can refer to a whole host of minerals, the one we're most acquainted with is sodium chloride, which has some quite useful properties.
Chris - Salt: it absorbs water and, therefore, it starves bacteria of water. Therefore it can stop the food degrading and going rotten so salt is a fantastic preservative and this was recognised many, many years ago. For example, the Egyptians, for the mummification process the way that the pharaohs bodies, and the food, and the pets of the pharaohs were mummified was by basically embalming them with salt to draw out the moisture. Also salt, because of its preserving properties, it's also been used in the past to preserve food. So, before we had refrigeration, we'd have to actually put salt into them and, again, it's to draw the moisture to stop them becoming rotten. That allowed, for example, armies to transport food over large distances to keep the fighting force fed. It's had an illustrious history in the past and, probably we're a bit more dismissive and we don't really think about it too hard because it's so cheap, whereas in the past it was actually a huge valuable commodity.
Georgia - Indeed it was. As well as enabling armies to march these huge distances with food, Roman legions were even sometimes paid in salt and this is where we get the word "salary" from. Salt was once worth its weight in gold because it was so hard to find but nowadays we can pretty much all we need from the sea, so it's not seen as such a valuable commodity. However, the sea is not the only place we find salt, it's also buried within the earth and this is where it becomes valuable in a different way to researchers like Chris.
Chris - Salt is this unique mineral, this unique rock and when you actually start to bury it, it actually starts to flow like a fluid rather than breaking in a brittle fashion like most people envisage a rock does if you stress it too much. So, we're interested in how salt flows and then how it deforms the earth's crust as well, and then the landscapes that are generated or the seascapes if it's below the earth's surface, that are formed as a result of that. So there's an inherent scientific value for us as scientists to understand how the earth's crust deforms as a function of how salt moves but, from an applied point of view, it's hugely important for the oil industry as well. This being because salt is an impermeable rock. That means that it's, actually, very hard to flow fluids or gases through that rock body, unlike sandstone or limestone, where we have small spaces in the rock where we can actually store hydrocarbons so we can store oil and gas. The salt is impermeable but that means if we put the sandstone against the salt, so we put permeable rock against impermeable rock and we can actually stop the migration of hydrocarbons and trap them. So a lot of the work we do is quite applied in terms of looking at how these salt structures form and how they can lead to the trapping of large volumes of hydrocarbons.
Georgia - And if that doesn't convince you it's important, I asked Chris to paint me a picture of a world without salt.
Chris - It's a very interesting question because some of the great offshore basins of the world contain salt so, for example, offshore Brazil where we work. If you were to just physically remove all the dissolvable salt material from there, the earth's seabed would collapse and you'd probably trigger giant landslides off the Brazilian coastline. I mean, in places like Cheshire, if you remove a lot of that salt from beneath the earth's surface, you'd have a lot of subsidence, you'd have presumably rivers being rerouted. You'd obviously have huge threats to infrastructure as well, like gas pipelines, telecommunication pipelines as well. But it sounds like a good - I'm not sure horror movie, but certainly an adventure movie of sorts.
Georgia - Well, I hear they're looking for ideas so...
Chris - Yeah, yeah, yeah... it would make good TV!
31:17 - What happens when you eat too much salt?
What happens when you eat too much salt?
with Dr Viknesh Selvarajah, Addenbrooke's Hospital, Cambridge
As a nation, the UK are above the intake guidelines for salt, which, for an adult, is 6g per day. To put that into perspective, there's about half a gram in a small packet of crisps, or one ham and cheese sandwich. But what does salt do to our insides? Viknesh Selvarajah from Addenbrooke's Hospital, in Cambridge, researches the impacts of salt and has a very unique perspective on the effects of high blood pressure, as he explained to Chris Smith...
Viknesh - I am a researcher in salt related disease and I had a stroke last year, interestingly enough. I had a bleed in my brain that was typical of a hypertensive stroke, which is a stroke you get with high blood pressure
Chris - Now we should be clear here. You're in your 30s. It's very young for someone, because most people who have strokes are older?
Viknesh - Yes. I had normal blood pressure, I had a healthy diet and I was a runner. So that was really unexpected and unlucky.
Chris - What happened that day?
Viknesh - Well, I was running a half marathon. I came back, I felt unwell and, about eight hours later, I lost my ability to speak. I lost all power of my right side, I lost my vision and I collapsed. I basically was close to dying but, fortunately, the bleeding stopped just in time for me to avoid surgery. The cause of the stroke was never clear.
Chris - Well you have made a very good recovery. Admittedly, you do struggle a little bit with movement...
Viknesh - I do.
Chris - ... but for someone to be in that state and to now be being interviewed on a radio programme. That's a dramatic turn around.
Viknesh - Certainly. My wife has been very supportive and I have done a lot of physio, and we were actually drilling holes, hanging up curtains this morning. So, it's been a long, long journey but I've been improving slowly and steadily.
Chris - For a kidney doctor who spends a lot of his time worrying about his patients' blood pressure, this must give you enormous insight into what the consequences can be?
Viknesh - Certainly. I've always told my patients to watch their blood pressure because high blood pressure is associated with stroke but, from now onwards, I can tell them I know what it feels like to have a stroke and I know nobody wants to have one.
Chris - What is the relationship between salt and blood pressure? What's that guidance based on - what's the evidence?
Viknesh - Over the last 100 years or so there's been a number of studies looking at the relationship between salt intake and blood pressure and, without a doubt, it's right to say that populations which consume more salt have higher blood pressure. What is also interesting is we used to think that increasing our blood pressure with age was inevitable when, in actual fact, with populations with low salt intake such as indigenous populations, you don't see a rise in blood pressure with age.
Chris - How do you know, when you talk about indigenous populations, that this is not a genetic thing? These people are all genetically the same and whether or not they add salt to their diet is just a confounding variable. It's one of these bystander effects, it has nothing to do with the reality of the blood pressure.
Viknesh - In the very large studies carried out more than 50 years ago called the Intersalt study, looking at indigenous people in their own environment and those people who move to the cities, and they watched these people change when they entered different environments and had more salt, their blood pressures went up.
Chris - Do we know why?
Viknesh - The actual mechanism for salt increase in blood pressure is debatable. Most people think that increasing your salt intake increases the amount of blood volume and that pushes up your blood pressure.
Chris - Why should eating more salt increase your blood volume? What's the mechanism of that?
Viknesh - Sodium controls where water goes, so the extracellular volume, which is one third of all the water in your body, tends to be bound to sodium. So, if you eat more sodium you tend to drink more and you tend to keep more volume in the extracellular space.
Chris - So if there's more water in the blood vessels, they're stretching the blood vessels more so, therefore, the pressures going to be higher?
Viknesh - Exactly.
Chris - Why do we think that people's salt intake has risen in this way?
Viknesh - It's interesting. Mose of the salt that we eat isn't from the salt that we add to our food. It's actually from processed foods. Things like bread, cereals, cheese, sausages and bacon. We've become very used to eating processed food and in processed food we have incredible amounts of salt. A slice of bread used to contain the same amount of salt as a packet of crisps. When this was highlighted by an organisation called CASH, the food and beverage industry realised they had to cut back on salt. And that was quite alarming that people were eating salt and not realising how much they were actually eating.
Chris - What you're saying is that because we all this intake, we've almost adapted to expect that taste and so when things don't have that much salt, we don't like them?
Viknesh - We certainly rely on salt to make food taste better. It appears that salt helps us to enhance the taste of sweetness and increase the taste of bitterness and make the flavour of the food taste more full. It's interesting that the processes by which this occurs is not fully understood but it certainly implies that salt makes our food taste better to us.
Chris - So what would you prescribe then - a better chef?
Viknesh - I would certainly encourage people to read the labels on what they buy. If you buy processed food like bread or meat, read what's on the labels. Very often, what you see is not what you expect. We advise that you eat no more than 6 grams of salt a day. You'd be surprised how easily you can reach 6 grams.
Chris - Where did that 6 grams come from?
Viknesh - A number of studies done over the years show that 6 grams is associated with ideal blood pressures and, therefore, reduce risk of heart attacks, strokes, and heart failure.
Chris - And what proportion of people do you think actually hit that 6 grams a day target?
Viknesh - The minority. The most recent survey called the National Diet and Nutrition Survey, the average salt intake for a male in England was 9 grams. The average salt intake for a woman was 7 grams so, overall, we are still eating too much salt.
38:34 - Can we make plants grow in salty soil?
Can we make plants grow in salty soil?
with Sandra Schmoeckel & Mark Tester, KAUST
Too much salt in your diet can be risky for your health, and the same also goes for plants. But as the human population increases, and the amount of land available for farming drops owing to the effects of climate change, finding salt-free soils, and salt-free water for growing food, will be problematic. Chris Smith went to see two plant scientists, Sandra Schmoeckel and Mark Tester, at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia. They're looking at a South American plant which can tolerate large amounts of salt, to see how it does it...
Sandra - In front of you in the little cup you can see quinoa seeds. So quinoa's quite interesting; it's sort of cooks like rice; tastes a little bit nuttier. The interesting thing is that it has more protein than other cereals like rice or wheat that you would eat. It's gluten free and it has a really interesting composition of proteins because it contains lots of essential amino acids.
Chris - And so why are you interested in this?
Sandra - We are mainly interested in it because it's extremely salinity tolerant. So, if you water it with half sea water, you still get two thirds of its yield.
Chris - And Mark - we're not accustomed to growing plants irrigated with seawater so why is this even a consideration?
Mark - The world's running out of water. About 40% of our world's food is grown under irrigation and a large fraction of that is exploiting groundwater resources that are being depleted. It's an unsustainable extraction, we can't keep going the way we are. We both have to be able to use the lower quality water that we have got left and we need to start considering opening up new water sources, and the obvious source is seawater.
Chris - That means you either got to now find plants that like growing in seawater or what, change the plants so they can tolerate seawater?
Mark - Or a bit of both. So what we need to be able to do is make plants more salt tolerant so they can be irrigated with salty water. So what we need to be able to do is partially desalinise the seawater, increase the tolerance of some of our crops, then we might be able to develop a whole new agricultural system based, ultimately, on seawater.
Chris - And Sandra - how are you approaching that? What are the steps that you're taking to try and turn this quinoa from something that will grow in saltyish soil in South America into something that could be a viable agricultural product?
Sandra - There are lots of quinoa varieties. Not all of them are really useful at the moment for farmers because they have different heights, they have different colours, they're very various. So there still has to be lots of breeding to fit the economic traits that the farmers would like to scale it up to industrial scale. The other really big problem we have is these quinoa seeds have bitter compounds on them which we call saponins. They are soapy molecules that have to be removed with lots of water and...
Chris - Do you know why they're there?
Sandra - Yes. We don't have experimental evidence for it as such but it has been observed that in fields where you have quinoa growing with lots of saponin, you have less birds feeding on the quinoa seeds.
Chris - So it's a bird deterrent but, because it's bitter, it's also a human deterrent and you'd like to get rid of it?
Sandra - Exactly! So the humans don't like the bitter taste of the quinoa seeds so it has to be washed off before it's useful for human consumption.
Chris - How do you propose to do this then? How are you going to get versions of this plant that don't make those seeds with those compounds in them?
Sandra - There are some varieties of quinoa that contain few saponins but these are not really useful for any industrial use at the moment. So we have looked at a quinoa variety in real detail, so we've taken the genome, and we're sequencing the genome, and looking in really great detail. And we also, because we know some of the lines that contain few saponins, we can breed that together with the lines that contain high saponins, and then we go down a few generations. And then, based on Mendel's laws we know that one quarter of the offspring will contain no saponins and the others will. So now we can compare the genomes because we have all the detailed information and, hopefully, we'll be able to nail down that gene that confers these saponins and is responsible for that. And, hopefully, we'll find a way, using modern technologies, to reduce that amount of saponins or we can just breed the sweet line with commercial lines and look for that marker of sweet, so low saponins, and then continue the breeding and make the plant sweet.
Chris - How realisable is this?
Sandra - I think we're pretty close. The genome - we have that already assembled. We are on the way. We do have the lines that I talked to you about. We have bred the sweet and the bitter lines and we have grown them. We have analysed the amount of saponins we have in there. What we now need to do is bring those two bits of information together, overlay them, and then look for the genes.
Chris - What about the salt tolerance that Sandra's mentioned, Mark? Are there other things that the genome will unlock for you and inform how this plant handles salt so well so you could put it into other plants?
Mark - That's exactly right, Chris. What we're doing is using the genome both for improving the quinoa and its agronomic properties that Sandra's just described and, also, learning from the genome and from quinoa. It really is an amazing plant - very salt tolerant. Really, the main thing is to learn how it's so salt tolerant and then transfer that knowledge into other crops, which are currently established, but more salt sensitive. The extreme example being rice, which feeds half the planet, but is very salt sensitive. What's particularly remarkable about the plant is the leaves taste salty. They've got a lot of salt up in those leaves. How does a plant tolerate that? How does that plant keep green, and keep photosynthesising, producing sugar, growing grain? That is remarkable and I'd love to learn that because plants like rice and wheat are pathetic at that.
44:42 - New ways to desalinate seawater
New ways to desalinate seawater
with Noreddine Ghaffour, KAUST
Fundamental to human life is a supply of fresh water. And in many countries, that's in short supply. One approach is the "desalination" of seawater. But this is a very energy hungry process. So are there better ways of doing it? Noreddine Ghaffour at KAUST in Saudi Arabia is working on some of them. Chris Smith dropped by to his office, admiring the view over the university campus...
Noreddine - So here we are in a very special place, which is KAUST, and you can see it's quite green but this is through irrigation. There is not rain.
Chris - If I just go outside to the walls of this campus, it's pretty much desert, isn't it?
Noreddine - Yes, it is but, this is the winter season. If you come to us in the summer then it is much, much, dryer than this one.
Chris - I mean, this whole campus has got fountains, it's go water features and, as you say, very, very green - lots of trees and plants. Where's the water for that coming from?
Noreddine - This water comes from a desalination plant. Desalination plant means we are making freshwater from seawater and here, as you can see, we are in front of red sea water.
Chris - The Red Sea. I mean it should be clear, it's not red seawater, it is the Red Sea we're looking at. It's very salty?
Noreddine - It's very salty.
Chris - How do you deal with the rhyme of the Ancient Mariner "water, water everywhere and not a drop to drink." How are you solving this?
Noreddine - Yes. That is the main issue here and, from that concept, water desalination technologies have been developed. So the reverse osmosis concept is using a membrane. It's a semi-permeable membrane but very fine, very small pores to the point where there is no pore, and we try to push seawater from one side of the membrane. But this membrane is very smart and allows only fresh water to pass through its pores or the structure of the membrane.
Chris - So, the water molecules can slip through but the salt particles are kept on the other side - they can't get through?
Noreddine - That's the situation. But, in order to do this, we need to overcome what we call the osmotic pressure. What is osmotic pressure? Each seawater has it's own osmotic pressure depending on the concentration of salt. For example, her in the Red Sea, the osmotic pressure is 30 bars. So we need pressure to pressurise seawater much above 30 bars in order to get this fresh water from the other side.
Chris - So, in other words, if you've got a very, very concentrated strong salt solution that's trying to pull water into it. So you've got to push the water really hard through the membrane and keep that push on, otherwise the water would just come back into the salt?
Noreddine - That's what makes this process very energy intensive. Just to give you an example, to produce 1 cubic meter of fresh water from the Red Sea, we need 4 kilowatt hours. It's something like 50 elephants pulling something.
Chris - Tell us something about the new things that you're trying to develop here to surmount some of these problems.
Noreddine - What we are developing now is to be as close as possible to nature. For example, our body is full of membranes and we call those forward osmosis membranes. So by nature, if you put that membrane and you put two liquids from both sides of the membrane. One liquid is fresh water, the other liquid is salty water. You do nothing - no pressure, no temperature, nothing. By nature, the liquid of the low concentration starts to move towards the salty place. This is by nature, we don't push anything.
Chris - That's just straightforward osmosis isn't it?
Noreddine - Yes. So what we have as a concept. In any place we need water, we have a lot of waste water. We are using that water then we throw it. So we put waste water in one side of the membrane and on the other side we put our sea water, So according to what I explained, what will happen is the dirty water, which is the wastewater, will start moving towards the seawater but this membrane only allows clean water to pass. All the dirty bacteria and this suspended salt will not pass. And what do you think we get? We are diluting seawater because of that process. Diluting seawater makes our feed for reverse osmosis very energy efficient, why?
Chris - I get it. Because you're now getting proportionally much less salt.
Noreddine - And this will reduce the energy consumption significantly. So if you have diluted seawater, which is something equivalent to brackish water, let's say, then the energy required for reverse osmosis is much, much, less. Half or even maybe less.
Chris - Other techniques that you're developing?
Noreddine - Absorption desalination. It's thermal based, but it's a new process. We are using an absorbent like silica gel it's a sand. If you put everything under vacuum environment, the silica gel or the absorbent will absorb water vapour from the sea. Seawater flows into an evaporator at it's ambient temperature, ambient pressure, nothing to do. And that evaporator is connected to beds filled with absorbents, as an example, silica gel. By nature the silica gel with create a vacuum because gel by nature will absorb means we will suck water vapour from that seawater. And then when the absorbents are saturated with vapour, we heat the silica gel using solar energy, because we need 50-60 degrees centrigrade and when the vapour is released from the silica gel, it goes into a condenser to condense it and with this we are producing very high quality water.
Chris - In a nutshell then. The water's pulled out of the ocean, goes into a chamber where it just naturally evaporates because connected to that chamber is a very dry bed of silica, which is sand effectively. And that's pulling vapour out of the air and pulling the pressure down so more water wants to evaporate but the only things that's going to evaporate is freshwater. You're then using energy from the sun to bake that water saturated silica, drive off the water it's absorbed, releasing water that's fresh, clean, that you can condense and use, but then you recycle the silica back to start the process again. So, when I do the energy calculations for this, how much energy are you saving?
Nodreddine - With this we are saving more than 50% of the energy compared to reverse osmosis.
51:12 - Smart polymer desalination Down Under
Smart polymer desalination Down Under
with Lucy Weaver, CSIRO
There are many labs tackling the salty problem of finding fresh water, and one piece of research underway in Australia could use clever chemicals to sustainably grab the salt from seawater. Lucy Weaver, from CSIRO and runner up in Australia's FameLab competition this month, is looking at smart polymers...
Lucy - We've heard a lot about salt on the programme today and down in Australia we have a saltwater problem, and I don't just mean the fact that we're surrounded by it. Big industries, particularly the dairy and mining industries, produce a lot of salty wastewater that can't be reused very easily or cheaply. And water is a precious commodity in short supply across most of the country. So, as part of my work for the CSIRO, Australia's national research organisation, I'm investigating new ways to take the salt out of the salty wastewater so that the water can be reused rather than thrown away like some of it is as at the moment.
The way I'm trying to do this is by using molecules called smart polymers. To explain what smart polymers are, I want you to imagine that you're on stage in a theatre in front of a sellout crowd. If you look out over the audience, you'll see that they're all sitting in chairs in rows. Since you're all the way up on stage though, to you, those rows look a bit like chains of people. At the molecular level, polymers, also known as plastics,are also made up of chains. They are comprised of molecular building blocks, like the people in the audience, and these molecular links are held together by chemical bonds.
There are many different types of links that can be used to make different types of polymer chains and, depending on which links you use, you can give the polymers special properties. Some polymers can be made with links that allow them to respond to a stimulus and it's this ability to respond that makes some polymers smart.
Now, back in the theatre. Imagine that you bow and then the crowd applauds you. In this example, your bow was a stimulus and the response was applause. In the case of my smart polymers though, the stimulus is temperature and the response I'm trying to create is the binding and release of salt. I've made polymers that contain some links that respond to a change in temperature and other links that attract salt. All of these links are organic compounds in that they're made out of carbon, hydrogen, oxygen, and nitrogen atoms, and some of these links contain acidic and basic groups that are able to interact with the salt.
The way that I make these polymers is using a technique called raft polymerisation. Raft stands for reversible addition fragmentation transfer polymerisation, which is a fancy way of saying we can make polymer chains that are the right size and composition for our needs. So, if we add some room temperature, salty, wastewater to my smart polymers, the aim is to get them to latch onto, and soak up the salt leaving behind clean water which can be collected and used. But, rather than throwing the used, salt laden polymer away, if we increase the temperature just a little bit, perhaps with some help from the sun, this change in temperature makes the smart polymer shrink and coil up. This process could potentially squeeze out all of the salt which can then be removed. Then, if we cool things down again, the polymer chains uncoil and we're back to square one ready to bind more salt.
In real life, this heating-cooling process can happen again and again and the polymer chains, in theory, will never get tired. If my experiments are successful, this process of generating cleaner water could potentially cost much less than current methods and could use much less energy as the polymers are sensitive to very small changes in temperature. And so, I think you'll agree, the potential of smart polymers deserves a round of applause!
55:35 - How does food change when we cook it?
How does food change when we cook it?
We put this question to geneticist Giles Yeo.
Giles - Cooking had a very important role in the evolution of humankind because what it did was increase the availability of calories. Now what do I mean by that?
If you assume 100 calories of sugar - that's 100 calories, okay, because there's no processing required. If you assume 100 calories of celery or 100 calories of sweet corn, then I think you can tell in the loo the next morning after you've had the sweetcorn, not all the corn is going to get absorbed into you. What cooking does is to actually increase this availability. So, if you take the corn and put it in a stew, you end up for any given mass, any given amount of food is get more calories from it. And this clearly then played a huge role because you put in the effort to pick food, gather food, hunt food and clearly the more you get from that effort, the more likely you are to survive. So, what cooking does is take the same amount of food and allow you to get more calories out of it.
Emma - So does cooking actually make food more digestible?
Giles - Cooking makes certain types of food more digestible by beginning the breaking-down process. Some foods will never be digestible by human beings. Grass is probably a good example. You need a rumen for that, you need specific type of bugs. But yes, cooking does make certain types of food more digestible.
Emma - Which foods would we be unable to digest if we didn't cook them?
Giles - That's an interesting question. I think an interesting thing to that is, actually, sweet corn is a very good example. Where, in the kernel form, most of it doesn't get digested. The interesting thing about that is that if you then actually break it down into flour and bake and eat it you can actually digest a lot more of it. So that's a perfect example where you make cornbread and clearly you don't poop out cornbread the other side. Corn is a very good example where cooking, processing, turning it into cornbread makes it digestible whereas the other is not.