Why is phosphorus important for life?

01 June 2018
Presented by Chris Smith.


A germinating seedling


Do white rainbows exist? Why does putting cold hands in hot water itch so much? Do food additives cause cancer? How can you safely store breastmilk? How does race affect eye and hair colours? Plus, fighting off dementia by seeing your friends. Chris Smith joins Eusebius McKaiser to answer your science questions... 


Eusebius - Chris, good morning.

Chris - Good morning!

Eusebius - I don't remember the story of the week. 

Chris - The story of the week is how you can stave off dementia by getting a little bit of help from your friends. Do you know the tune? Can sing can you sing the tune for us?

Eusebius - I suspect I will. Yes. 

Chris - Get by the way a little help from my friend.  You'll probably have it as an earworm today.

Eusebius - I love it though, so it's not a bad one to have as an earworm. 

Chris - No it's alright. And an a good, a good message in there because what Liz Kirby, who is a researcher at Ohio State University, is saying this week - she's got a paper out which is in the journal Frontiers in Aging Neuroscience. She's actually tried to address this question which epidemiologists, people who study populations at a big level, have been telling us this effect is there for years but we weren't really sure which way round things work. In other words, people who have big social networks; they sing in choirs, they play musical instruments, they go to church, they have loads of friends over, they socialize a lot. They have a much lower risk of dementia than people who have a lower social network score. Now is that because people who are demented or have age related cognitive decline tend to eschew company and they dont socialize very much. Or is it that having that big social network reduces your risk of developing cognitive decline with age and thats what she wanted to find out. And shes done this series of experiments on mice, and what she does is either take couples mice so you take an old pair of mice. These are really ancient mice, they're a year and a half old which for a mouse is very elderly indeed. She puts a pair of mice together in a cage or she puts them into the mouse equivalent of an old age retirement village where you've got seven or eight of them all living together in a cage. And then while they're in that context they do various memory tests on them. They test their ability to remember the way out of a maze, also novel object recognition tasks where you put them in an environment with some objects and then you move one of the objects and you see if the mice notice. And the trend that strongly emerges is that the animals that are kept in big groups, the groups of seven which is the rodent retirement village setting, they do much better on these memory tests consistently than the animals that are just kept in pairs. And when they look at the brains of these animals, the animals that are kept in big groups have lower levels of inflammatory changes in their brains, probably consistent with stress we dont know, but they seem to have lower levels of brain attrition because of this inflammatory effect when they kept in big groups. So this suggests to us that actually being in a big group perhaps the cognitive exercise of having to interact with people, individuals, language exchange, keeping up with the Joneses, working out what they want, thinking about how to reply to people, that sort of stimulus is brain exercise which appears to keep us cognitively fitter into our old age. So she's saying when you're planning your retirement don't eschew company, try and plan your retirement around maintaining your contact with people and even as your mobility may decline a bit because this does appear to be extremely good for your brain aging.

Eusebis - That sounds so fastinating. I've got millions of questions. Can I just ask one before we go to the callers. So I'm thinking, and forgive me you know I'm just a little BA student, but I'm thinking here if part of the basic intuition is that in a group you get to exercise the brain like you'd maybe say a muscle, if I can use a weak analogy, Chris. I wonder if I was live alone, or if I was the pay of mice rather than in a group of mice, if I had other stimuli however could they do the same? So, for example, if I read lots of literature even though I'm a lonely figure who don't socialise a lot could I get similar kinds of stimuli from other sources not necessarily humans?

Chris - Well one has to bear in mind that we don't know, for example, what role exercise plays in this as well because we know exercise is extremely good for your brain. It encourages the birth of new nerve cells and it might be that living in a big group of seven or eight mice increases the amount of exercise you take. Although they did try and control for that because they said the mice weren't any fatter or thinner which they would be if they were being more sedentary or less sedentry. At the same time, humans are all different and some of us are loners, some of us like to live on our own and retreat into our own man or woman cave and read books and immerse ourselves in the internet for a while, and that's stimulation as well, so it's important not to generalize too much. But what does appear to be a consistent trend for the average person is that social contact is important. Now that's not going to be true for everybody. So there will be some people for whom actually that's a very stressful and unpleasant existence which will make life feel like you're living forever even if you're not. So it might not suit everybody, but for your average person it probably is beneficial to have more social contacts and a bigger social network.

Eusebius - Fascinating. Sue, our first caller today. Welcome to the show, Sue.

Sue - Hi, good morning.

Eusebius - Good morning. Go ahead. What's your question for Chris?

Sue - Thank you. Something that I've saw here on the farm where we live in the Western Cape which I can only describe as a white rainbow. It was the shape of a rainbow. It was really it was a bit of moisture in the air but it was plain white and when it disintegrated it sort of collapsed in on itself, if that makes any sense.

Eusebius - Oh wow. Chris, have you ever encountered something like that?

Chris - Well I have seen some rather strange cloud formations. And good morning Sue by the way. You don't mention how high this was in the sky and therefore whether it could well be a cloud formation. Because, obviously, one of the things people who live at the southern tip of Africa now are well familiar with is the exigencies of the weather. You're right at the forefront of being battered by all of the weather which comes from the very far south and Antarctica and so on. Theres a lot of warm ocean, a lot of cold ocean, so theres a lot of air mixing that goes on, and a lot of wet air mixing, a lot of dry air mixing with a lot of dry air. So I think it's possible what you could have seen was a cloud formation because when you get big masses of air which are saturated and warm, hitting lots of air masses which are very cold you can get condensation, very abrupt rapid condensation of the moisture into something that looks a bit like a giant cloud all of a sudden. So clouds will literally form where this air masses is intermingling. I wonder if thats what you saw and it wasnt a rainbow it was actually a cloud. But because its obviously little water particles they're going to reflect a lot of light make it look very white.

Eusebius - Thank you so much for your question Sue. Let's go to Parktown. Corsi, good morning.

Corsi - Hi Eusebius? Dr Chris, I just want to find out that it's cold, okay. So I just wanted to find out why is it that when my hands get terribly cold - my hands and feet, and then I get em to the fire or warm water they itch like I want to be a hospitalized? Why is that a bad idea and why does that happen? I swear it happened, it happened. I got so cold I went and I put my hands in the sink in warm water. It's too late, I wanted to die. I need to find find out why that happens and why is that a bad idea?

Chris - I'm laughing out of familiarity, not laughing at you, and because I've done exactly the same thing and I know how excruciating this is. I suspect that in the same way that if I make my hands very cold and then warm them up quickly, or my feet, I can get chilblains - the posh medical word for that's erythema pernio - it appears that there's a number of things that go on. When you make your peripheries, your extremities, extremely cold the body responds to preserve heat in the body by narrowing the blood vessels in those peripheries, so it limits the blood flow through your extremities. When you warm them up abruptly then the blood comes rushing back to resupply this tissue which has not had enough blood flow for a while and therefore there can be other waste products and things in the tissues which is why you get this whats called a reactive hyperemia, you get an exaggerated circulation transiently. I suspect that when this happens, what it also does is it irritates a population of nerve cells which supply skin which selectively convey itch sensations and they connect to your spinal cord and say this patch of the body is itching, trigger an itch sensation. And it's there as a defence mechanism normally because the kinds of things that make you rich are irritants, and not just Jacob Zuma type irritants, but irritants like chemical irritants in the environment, and these things include parasites and things trying to burrow through your skin. So they're there for a reason but they can be fooled into into being activated by extremes, and extremes of temperature can trigger these nerve cells off. So I think it's probably a combination of the blood rushing back in, opening up of blood vessels, and also irritating this itch selective group of nerve fibres. And I think some people are much more sensitive to this than others because there are people in the population who do get chilblains and do get something called Raynauld's phenomenon, where you get a very very profound constriction of your blood vessels in your extremities. Very painful, and so I think probably you're at the end of the spectrum of people who get these symptoms more markedly than other people.  

Eusebius - Okay. Let's got to University Estates. Ray, good morning and welcome!

Ray - Good morning. Hi Eusebius and Chris. Look, I was reading Arthur C. Clarke's short story Before Eden, and it's set on the planet Venus. Human scientists are leaving the planet and they leave behind their refuse and waste and an emerging life form - a plant - ouses the rocks under which this is all buried and starts feeding on it. And then Arthur C. Clarke says: the most precious of all foods was needed, phosphorus, the element with which the spark of life could never ignite. What is it this prosperous? I've never heard this before.

Chris - Ah, good morning. What an interesting quotation because of course we're seeing this playing out. We reported a story here on 702 a few months ago where researchers published a bacterium which is capable of degrading PET, one of the commonly used forms of plastic, and that bacterium had been discovered in a waste bottle recycling plant in Japan. It was a bug called Idionella sakaiensis and it happens to have an enzyme which they've dubbed PETase, which can break down plastic. So in other words if you if you put loads of rubbish in a place, eventually life will find a way to tap into that and use it as an energy source. But where phosphorous comes in, and why the world actually faces a phosphorous shortage is that phosphorus is absolutely critical for our DNA. In order for cells to grow they have to copy their DNA, and DNA has a backbone of sugar molecules linked to phosphorous and linked by phosphate groups. So you cannot make more DNA without a steady supply of phosphorus and so phosphorous is often the rate limiting reagent or chemical in growth, and so plants and farmers know this very well. Farmers put this on their soils in order to get good yields from their crops because plants also have their growth retarded if they don't have enough phosphorus. And then the plants take up the phosphorous and then when we eat plants we get the phosphorus that way. You lose a little tiny bit in your urine. But that's why phosphorus is so important. It's absolutely fundamental to DNA and it's chemical relative RNA which is what underpins all of our molecular biology, our genetics.

Eusebius - Behosey, good morning.

Behosey -The question is regarding food labelling. If you look at quite a few food labellings you find the inscription there E627 or E150, and so it goes on. My question is what does that mean and how customers [**] addatives to foods? And two, pasturised milk. In my days you used to get it turn sour in a day or two after you've bought it. Now it goes on for four months down the line and you're guaranteed that it doesn't go off and this is just exactly what is happening. And then it goes on to label that "not formulated for infant feeding". Can you explain that and [**] seems to be out of control of late? 

Eusebius - Thank you Behosey. A wonderful set of questions there Chris.

Chris - Yes, well first of all let's look at these E numbers. These are numbers which designate chemicals, substances which are added to foodstuffs. Just because they're added doesn't mean they're not natural. Vitamin C (ascorbic acid) has and E number, so those numbers designate the presence of certain substances added. It doesn't mean that they are harmful to you and in fact they're they're definitely not in many cases. The reason researchers, food producers, manufacturers might add E numbers like vitamin C to a food is because vitamin C is an antioxidant, and part of the degrading process as food goes off is to oxidize various foodstuffs especially things like fats, and they taste nasty. If you add antioxidants then those things get in the way of the things that we'll be doing the oxidizing, soak up those reagents and stop them oxidizing the food so the food doesn't taste nasty later. So it tends to have a longer shelf life or it stays in good condition and pleasant to eat and consume for longer. That's one
example. Other forms of these E number additives are colors, so you might add a fruit dye to give food a red color. Beetroot contains anthcyanin, for example, and that's a deep red color. That has an E number and you can add those anthocyanins to food to impart those colours. So they're not necessarily harmful, but at the same time, you should read the label and see what's in them.

Now looking at milk, this is an interesting one. The question about why it says "not for infants" is that the milk you're buying from the supermarket is by enlarge cows milk. This is a different combination of nutrients which are ideal for a growing calf, they're not ideal for growing human. Breast milk from a human has a very different composition, different amount of fat, different numbers of sugars, some other things that are in there which are not present in cows milk and vice versa. So you can get health problems if you were to feed a little baby on cows milk as though it were human milk it would end up with problems. Often there's not enough iron there and there are also chemicals in cows milk that can soak up iron and the baby could become a bit anemic for example (low red blood cells), so that's why they warn you this is not an infant formula. It doesn't contain all of the micronutrients in the right context and in the right proportions that a human developing infant needs, so don't use it to such. Fine to give it as a top up or to give it with other things, don't use it exclusively is what that means.

Pasteurization invented by Louis Pasteur. That process involves heating milk transiently to more than 60 degrees for a period of time to kill off the microbes which are naturally present in milk and which would degrade milk by oxidising various things in the milk and turning into cheese. If you kill those microbes, the bacterial burden in the milk is lower to start with. Therefore if you keep the milk cold it should because it contains less contamination to start with, go off more slowly and therefore it will last longer in the fridge, and you won't be drinking cheese on your cereal.

Eusebius - Clare, good morning to you.

Clare - Hi, hi. It was quite interesting hearing that at the end of your last thing is about milk. My question actually about expressed breast milk. I came across something last night actually about high lipase in expressed breast milk, and it goe off or go bad when kept the fridge. I think people about fixing things that are problems. I've been exclusively pumping for my baby for the last 17 months and I think we go through it quite quickly but never really gets an opportunity for that to happen. But a few months ago I did notice, when he was going through a hunger strike, that my breast milk wasn't feeling great or tasting great. My question is really just have you heard about high lipase before in breast milk? Do you know how that happens and is there any way of preventing it? Because it seems a way to treat it is by scolding it as you've expressed it, but I'd like to know if there's a way of getting around that? Is it diet, or what causes that high lipase in the first place?

Chris - Hello Clare. Right, the bottom line is that fresh is best with anything. We all know that. And so if there is a way of not having to store things then they tend to be better. And the same goes for breastmilk because this is a living tissue when it leaves your body. It's been made by the glands and glandular tissue in the breast. There are cells in there, there are other chemicals which are added so that the milk is ready to use, its pre warmed and it's in just the right sort of context, as it were, chemically for a baby to absorb those nutrients and use them. Now the longer you store something, the longer opportunities there are for other chemical reactions to happen. For cells to break down that are in there because there are some cells in there. Release various enzymes which are in those cells which will break things down. And there are also things that the breast secretes to get the milk ready so that it's going to be used there and then and the human breast has not evolved with putting something in the fridge in mind or putting something in the freezer. That said, breast milk is still going to be better than having some other alternative which is not breast milk. So it's a balancing act and one shouldn't feel you beat yourself up because you've had to store some breast milk. That's perfectly reasonable. Breast is definitely best but, at the same time, the idea that giving the stuff as fresh as possible with the minimum storage time is also the best approach. So if you can minimise the storage time you'll have the best outcome, but you'll still have a good outcome if you use it having kept it for a little while. But don't keep it for too long because obviously the longer you keep anything the greater the risk of other chemical reactions going off which spoil the flavour and the taste, damage some of the nutritional value and it might become infected, and then you could give your baby an infection which you don't want either.

Eusebius - I'm loving your tweetable insights today Chris. Breast is definitely best.

Chris - Yep. Breast is best. Definitely, definitely the case. Always the case.

Eusebius - Hi Min, good morning.

Min - I've got a question: the different races on the planet. The Indian people, the Chinese people, the people of Africa to Europeans, the white race. Why do some of the races of the people are born with the same colour hair and eyes, whereas most of the white race they are born with different colour hair and different colour eyes? Has this to do with the DNA or is it to do with anything else? 

Eusebius - Did you get that Chris?

Chris - I did. And the thing is that the reason we look the way we do is absolutely dictated by our DNA. And the DNA you actually carry is dictated in turn by the environment in which your group of people have evolved. It's only in the modern era that we have aeroplane's which are ferrying people from one side of the Earth to the other in under 24 hours. Unless you're on Virgin and then you know they probably won't arrive with any luggage or anything. They treat me abysmally. But anyway, in the modern era we are very very mobile but historically we weren't, and populations were born and died in the same geography pretty much. And that meant that the genes that you carried, and the genes that made you successful as a group and a race and a population were selected enriched and concentrated on your particular patch of the Earth, and so that's why certain traits got concentrated. There's a very good reason why people who are Chinese look that way. Those genes would have given you a particular set of characteristics that meant you were successful in that environment.

Now if you look at places on Earth where it's very very hot and sunny, having dark skin, having dark hair is a massive bonus because sunlight contains ultraviolet, and ultraviolet will actually break down folic acid in your body, and folic acid is absolutely critical for the formation of new cells. And if a woman does not have enough folic acid and she gets pregnant then she has a baby, an increased risk that her baby will have a neural tube defect something like spina bifida. So having dark skin in a very hot place is extremely beneficial. When you go up to Europe, you end up with places like my country where the sun doesn't shine for half the time. Well even when it should be shiny it is very very weak. And so if you have dark skin you don't have a folic acid problem any more, but you do have a vitamin D problem because the ultraviolet also creates vitamin D in your skin, so then you end up with bone problems and calcium problems. So people in Europe then evolved to have whiter skin because they could then access more vitamin D being synthesized in their skin. The loss of the dark pigment, which is a very dominant pigment and would mask other characteristics, unmasks other coloration which is in the skin and in the hair. And you end up with other forms of melanin, one called phaeomelanin, which is very yellow being in your hair so you see blonde hair tones. And also, because you actually have lighter skin, you can see a broader range of skin tones because you don't have that very strong production of melanin which would overwhelm and mask those other underlying colours. That's why you tend to see this apparent increase in diversity when you're outside of Africa, but genetically Africans have the greatest genetic diversity of all races on the Earth.

Eusebius - Fascinating. Thank you so much Chris. Have a lovely weekend.


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