Associate Professor Deborah Sloboda is a scientist from McMaster University, Hamilton Canada. She is a Canada Research Chair in Perinatal Programming (that’s a title, not a place to sit!) and the Secretary of the International Society for Developmental Origins of Health and Disease. Dr Sloboda is interested in fetal development – she investigates the relationship between what a mother eats and does during pregnancy and the growth and development of her baby, in particular how it affects her children’s puberty, reproduction and metabolism. Her website link is here, her lab is on Facebook, and has recently been in the news.
Puberty – that time in life when everything changes; your brain, your body, and your behaviour. We all go through it – humans and animals alike. It is a normal process in our life but WHEN it happens (in humans)– well, that has now changed. About 100 years ago, girls were going through puberty around the age of 17. Nowadays that age is a lot lower – it’s more like 12.5 years. So, why the change? What’s going on? And what regulates this timing anyway?
Well first, we have to consider WHY we go through puberty. This is a biological question, but let’s consider it from an evolutionary point of view. It might seem like an obvious answer – puberty happens so we can have children, to pass on our genes to the next generation before we die. Let’s face it, it’s the reason that all organisms live and strive to survive. So if puberty is about producing the next generation, then puberty has to happen when we can support a pregnancy and raise babies, and it has to happen before we die (obviously!). And the great thing about biology is that it uses information from our environment to determine when that time best suits us (biologically) to pass on our genes.
So hang on, what happened over the last 100 years to change the timing of puberty? The most important thing has been improvements in our living conditions. Things like sanitation, better nutrition, vaccinations (i.e. controlling infectious disease) all improved the conditions that we grow up in. So all this environmental information tells our bodies, “Hey, its okay to go through puberty because you can handle a pregnancy and you can take care of babies – and you need to do this before you die”.
The environment tells us when to reproduce. Scientists already knew this – it happens all the time in the animal world. But recently we discovered something new. What we normally call “environmental influences” – like where we live, what we eat, our family structure – now includes our life before birth: embryonic and fetal life. What a pregnant woman eats, the medication she takes, the stress she encounters – these are all part of the “developing environment” and babies respond to this environment just as we respond to stimuli in our postnatal environment. Not only that, but we now know that what a pregnant mother eats also tells her daughters when to go into puberty, and potentially how many babies they can have and perhaps how long they will live.
Using animal models, we discovered that feeding a pregnant mother a poor diet (either feeding her less food than normal, or feeding her a high fat diet) results in her daughters going through puberty early and changes the number of eggs her daughters are born with, thus possibly changing their fertility. So the pregnant mother provides prenatal nutritional information to signal to her developing daughters when might be a good (or bad) time to go through puberty and also potentially how many children she can have.
We are a long way from understanding why all this happens, but we have some idea about how. The eggs that are used to make the next generation are formed during fetal life. All girls are born with their lifetime number of eggs and importantly they don’t make any more. So the developing environment can influence the growth, the number and potentially the function of the fetus’ eggs – resulting in changes to puberty and long term reproductive function.