Susan Ozanne, University of Cambridge & Lucilla Poston, King's College London
One factor which we know can harm your heart is being overweight - it makes you more likely to have high blood pressure and heart attacks, but - if you’re pregnant, it can also increase the blood pressure of your child, or even your grandchildren. Chris Smith caught up with two researchers who are looking into why this is happening. Susan Ozanne is from the University of Cambridge, and she outlined the evidence that this is indeed happening....
Susan - From human studies actually, some of the strongest evidence is when we look at children, currently living in the same household, born to the same parents, but from pregnancies that occurred either before or after the mother had bariatric surgery, so therefore from pregnancies where she was either lean or obese.
Chris - So bariatric surgery are these sort of gastric banding surgeries that help people to shed weight?
Susan - Exactly.
Chris - And you’re effectively saying look, we’ve got the same parents, the same environment. So the genes are pretty similar, the environment’s the same but the only thing that’s different is the weight, so you can compare the two?
Susan - So if you look at those children who were born from pregnancies after the mother had lost weight and she was lean. They are slimmer, they have lower blood pressure, and they’re more insulin sensitive so they’re less likely to get diabetes.
Chris - Insulin being this hormone that controls sugar?
Susan - Yes. So insulin is the major hormone in our blood which, when we eat a meal, makes sure the blood glucose levels don’t stay high. It makes the blood glucose go into muscle where we store it and also into fat tissue.
Chris - And when you say children, are we talking throughout childhood and into adulthood or are you saying just when their born? When does this effect manifest?
Susan - So you can see evidence for it very early on, but for the studies they’ve looked at people right up until their 20s and shown effects right from 2 years old right up until they’re in their 20s
Chris - Striking that something that should be happening when that baby is just in-utero, just 20 weeks, should have 40 years of legacy or more.
Susan - Or more because, as I mentioned, it can also, potentially, impact on the next generation as well.
Chris - How?
Susan - So we think what obesity during pregnancy is doing is impacting on how our DNA is used. So it’s not changing the DNA sequence but the genes that we’re using within our genome, and how much we’re using them differs, because of a response to the environment. It’s almost like you're in a library and you’ve got a whole load of books but it doesn’t mean to say you’re going to read all those books, it’s the ones you pick of the shelf that are going to determine which ones you read.
Chris - So we have a baby, it’s growing in it’s mother, the mother is determining the environment the baby grows up in. If the mother is obese, there will be some kind of change to the environment that the developing infant is experiencing, this has an effect of chemically changing the DNA and that effects what genes are turned on or off or how much…
Susan - Exactly.
Chris - So that affects the baby that is developing there and then, but how does that influence the next generation?
Susan - So that will determine how likely that baby is to develop diabetes, for example. How likely that baby is to have high blood pressure. How likely that baby is to have a heart attack. Now, obviously, that baby themselves when they become pregnant, if she’s more likely to get diabetes, for example during pregnancy, then you will again have an impact on the next generation even if her diet has been totally normal.
Chris - I thought you might be going down the route of well, if you’re having a daughter, when that baby is developing then inside her is her future ovary with all of her future eggs and, therefore, half of the genetic information of her children, your grandchildren in there.
Susan - Yes, and that will also contribute as well and, actually, the same thing is happening from sperm as well. So there’s more and more evidence to show that dad’s diet also impacts on the sperm and then how that will impact on the next generation.
Chris - As well as these so-called epigenetic changes, there are clues from animal studies that there may be changes going on in the developing brain. Lucilla Poston, from King’s College London.
Lucilla - So what we’ve done is we’ve made mice and rats fat. We’ve given them delicious things to eat so they’re very happy to do that, and they get fat when they’re pregnant. We’ve looked at the offspring as they’re growing up and we have found, just as has been suggested by the human studies, that the offspring do get fatter and they also have high blood pressure, and the focus in terms of mechanism is pointing towards an area of the brain which is called the hypothalamus and that area in terms of development is the womb is very susceptible to nutritional influence. So in the later stages of pregnancy when this area of the brain is developing, we know that nutrient hormones can actually change the way it develops. So you can imagine that if you hardwire the networks of the brain’s neurons, you might actually change either the blood pressure or the fatness of the child because that area of the brain is very responsible for controlling both of those outcomes both in terms of the hunger, the satiety of the child, and the blood pressure of the child.
Chris - So there is a physical change in the connectivity of the bits of the brain that are determining blood pressure, how your heart works, and also your future appetite if you are exposed, during development, to a sort of obese environment?
Lucilla - You can change the development of the hypothalamus by the nutrient hormones which surround it during development. That’s been shown experimentally, there seems to be no question about that. We can’t look at that in people, so we can’t categorically say this is happening in mums and their babies but the evidence from animal studies is certainly very positive that that could be one of the mechanistic pathways.