Skipped the gym yesterday? Oops – now your unborn kids, and their kids, are going to struggle with weight and cholesterol for their entire lives. If only you'd spent more time practising tennis, they'd inherit your devastating passing shot.
Or maybe not.
The nascent science of epigenetics, which enabled the research that won the 2012 Nobel Prize in medicine, is rewriting our understanding of how nature and nurture interact. Experiences in one generation can produce echoes in the next, contrary to what biologists believed for more than a century. But before you start feeling too guilty, it's worth taking a closer look at what epigenetics does – and doesn't – tell us about our future health and fitness, and how much of it you can actually control.
Your genes – about 24,000 of them – are encoded in the DNA you inherited from your parents and will pass on to your children. But DNA is only part of the story. A series of chemical markers determines which of those genes are switched on and which are suppressed, and these epigenetic markers (meaning "above the genes") are affected by your lifestyle and environment.
Most of these markers are wiped clean when your cells divide as part of sexual reproduction. But starting in the 1980s, a series of painstaking multigenerational studies hinted that some epigenetic changes could be passed on from one generation to the next.
The most famous study tracked the inhabitants of a remote Swedish region called Overkalix using generations of parish records. Among boys born in 1905, those whose grandfathers underwent a year of poor crop yields immediately before puberty (when sperm is maturing) lived six years longer on average than those whose grandfathers reached puberty after a year of bumper crops.
More recently, studies have shown that epigenetic changes continue to occur throughout life. In 2012, Swedish and Danish researchers reported that a single bout of intense cycling can flip epigenetic switches in muscle. Another Swedish team found that six months of regular exercise produced epigenetic changes in an astounding 2,800 genes in muscle and another 7,700 genes in fat tissue, leading to changes in how the body processes and stores glucose and fatty acids.
On the flip side, young men who were kept physically inactive for nine days exhibited epigenetic changes in the opposite direction, resulting in impaired insulin sensitivity. Similar results were seen after following a high-fat and high-calorie diet for five days.
Such findings have been eagerly embraced by those who argue that genes are not destiny. But the point can be stretched too far, warns science writer David Epstein. His 2013 bestseller, The Sports Gene, originally included a chapter on epigenetics, but he pulled it before publication because he felt the research was still too preliminary (the chapter was later published with a cautionary disclaimer on the futurist/sci-fi website io9).
As an example of overhyping, Epstein cites a recent pop-science book that used epigenetics to suggest that practising piano might make your kid a better piano player.
"It isn't as clear as 'I do A, so my kid is better at A,'" he said in an e-mail.
The Overkalix data, when examined in detail, shows just how counterintuitive and seemingly contradictory epigenetic inheritance can be. Starving grandfathers produced healthier grandsons; starving grandmothers, on the other hand, produced less healthy granddaughters.
Moreover, the examples of epigenetic inheritance that have been identified so far involve experiences during relatively narrow developmental windows – just before puberty for men and during pregnancy for women. While that means it's unlikely that your workout (or piano playing) will benefit your descendants, it does offer the most promising avenue for health advances from epigenetic research.
In a study published earlier this year, Dr. Daniel Hardy and his colleagues at Western University in London, Ont., found that rats whose mothers were exposed to nicotine during pregnancy showed epigenetic changes and developed higher levels of harmful fatty acids in their circulation later in life. If the same effect occurs in humans, it's an important addition to the ongoing debate about the health risks and regulation of new smokeless e-cigarettes.
Researchers have also studied various other factors that affect pregnant women, such as poor diet, body composition and stress. It's hardly news that maternal health during pregnancy can have long-lasting implications, but understanding the role of epigenetics may help to reverse some of these effects.
"I really am a believer that we can change the epigenetic environment, and change your outcome, with early intervention," Hardy says.
In some cases, that might be as simple as managing the diet of low-birth-weight babies after they're born to avoid too much rapid catch-up growth, which has been linked to impaired insulin resistance and high cholesterol in adulthood.
Hardy is also studying drugs that directly reverse some of the epigenetic changes seen in low-birth-weight babies, with promising early results in animal studies. Drugs that target epigenetic switches are already being used to treat diseases such as cancer and epilepsy, though the daunting complexity of links between genes and disease means that it's not entirely clear how these drugs work.
And in July, a pair of review papers in the journal Drug Discovery Today argued that researchers should seek to develop drugs that target the same epigenetic switches flipped by diet and exercise – but that goal remains far off.
In other words, epigenetics does have the potential to produce exciting health breakthroughs. But it doesn't let you bequeath your jump shot to your heirs, no matter how hard you practise. Instead, the takeaway message is about what you can do in your own lifetime – that diet and exercise can dramatically alter the expression of thousands of genes that affect health and athletic performance.
We already knew that practice makes perfect, but it never hurts to be reminded.
Alex Hutchinson blogs about exercise research at sweatscience.runnersworld.com.