You are what you eat, so the saying goes. And it goes without saying that a lifetime of poor diet, minimal exercise and smoking increases your chance of getting obesity, heart disease and type 2 diabetes. About two-thirds of all deaths worldwide are caused by such diseases. It seems, then, that we are a product of our own modern lifestyles. But research is beginning to reshape our understanding of how our health as an adult can be affected by events much earlier in our lives. It might actually now be more accurate to say that “we are what our parents ate”.
And while we often hear about the importance of eating well, being a good weight and having the right nutrients are in women who want to have a baby – less is said about how much these things also affect a man who is passing on his genes.
More than 30 years ago, David Barker and colleagues found that children who were small at birth were more likely to develop heart disease and type 2 diabetes as adults. From these observations, the Developmental Origins of Health and Disease (DOHaD) concept was established. Since then, hundreds of studies have strengthened the link between maternal diet during pregnancy, the growth of her unborn offspring and their health as they grow into adults. However, the role that a father’s diet may play in directing the growth and health of his offspring has been largely ignored.
While male fertility has been declining over recent decades, waistlines have been increasing. The link between high BMI and poor sperm quality is actually well established. In both men and mice, obesity decreases production of testosterone while increasing the production of abnormal sperm – sperm with damaged DNA and sperm with poor motility. Sperm from obese and overweight men are also less likely to fertilise the egg, promote the embryo to develop and less likely to result in the birth of a child.
However, animal studies demonstrate that the negative effects of male obesity can be reversed, simply through exercise. Other lifestyle factors including smoking, alcohol consumption and exposure to certain chemicals such as phytoestrogens (plant-based oestrogens) or drugs can also affect sperm quantity and quality.
Passing it on
We are now beginning to understand that a father’s poor diet can also affect the health of his adult offspring. One study found links between a grandfather’s diet during his teenage years and the risk of his grandson dying from cardiovascular disease in adulthood. Interestingly, no such link was seen between grandfathers and granddaughters, suggesting the effects were passed only down the male line.
Data obtained from animal studies is also helping to highlight the importance of a father’s diet for his offspring. In these studies, researchers can manipulate food intake very precisely, only changing a single aspect of the diet. Studies have looked at the effects of diets high in fat or sugar, low in protein or what might happen even by simply reducing the total amount the male mouse eats. In response to all these poor and imbalanced paternal diets, their adult offspring become overweight and have poor cardiovascular and metabolic health. Other studies have shown that feeding male mice vitamins and antioxidants can prevent their offspring from having poor health in adulthood.
One additional interesting question that is still unanswered is whether paternal age is a factor for the health of his offspring. Many studies report that sperm production declines with age and that their motility declines also. As men age, so too do the stem cells within their testes that produce the sperm. Therefore, sperm from older men can have higher levels of damaged DNA in them, affecting the development of the embryo after fertilisation. Some studies also report links between paternal age and higher rates of autism, schizophrenia and some forms of cancer in resulting children. However, there are just too few studies to state definitively the effects of paternal age on the health of resulting children and what the underlying causes are.
But it now seems clear that the health of a father can affect the development and well-being of his offspring. Poor paternal health can even affect the chances of a man becoming a parent.
The idea that our adult health is determined before birth is of great interest, especially for those who want to either point the finger or absolve people of behaviour they see as undesirable. However, care and caution is always needed when interpreting results and drawing conclusions from animal and human retrospective studies.
It is still too early to advocate specific diets or nutrients that will promote sperm production and child health for all intending parents. Saying that, couples wishing to become parents could do a lot worse than assessing their current lifestyles habits (diet, smoking, drinking) to see if any improvements could be made.