Macrocosm: Epigenetics, How Parents Can Pass Down Their Life Experiences to Their Children and Even Their Grandchildren

10'000 Hours

For many years, scientists thought they had the entire inheritance formula figured out. You get your DNA from your parents, and it determines many things about you, including what you look like and your likelihood of developing certain diseases. Scientists believed the traits we acquired during our lifetimes, outside of DNA, could not be passed down to future generations. This was all turned on its head when researchers started examining the records of a small community in 19th century Överkalix, Sweden.

Överkalix, is located in the arctic, a region not known for its ability to support vegetation. Still, some years the community experienced bountiful harvests and other years were marked by deadly famines. Citizens lived in a constant cycle of having too much to eat or not having enough. The researchers realized that the grandsons of boys who experienced a “too much to eat” season just before hitting puberty died six years sooner than their “not enough to eat” counterparts. It appeared to them that the grandfathers were passing down genetic information to their grandsons outside of simple DNA. Upon further research, scientists discovered that there is an additional layer of information that sits ‘on top of’ DNA controlling how our genes are expressed; they call this the epigenome.

The Genetics of It All

Scientists describe DNA as the blueprint of life because it contains all of the information needed to build an organism. Though it may sound strange, nearly every cell in your body has the same DNA. Yes, all 37.2 trillion of them. So then, how do cells differentiate? How does, say, a skin cell know to become a skin cell and not a brain cell?

The human genome consists of thousands of genes; in each cell, only some of those genes are actually ‘turned on’. Epigenetic mechanisms act like on-off switches, dictating which genes are silenced or expressed. DNA methylation, a common epigenetic modification, involves attaching methyl groups to the DNA double helix. This effectively silences a gene, ‘turning it off’.  

The DNA methylation slate is wiped clean twice in our lifetimes, but like some chalk residue remains after a blackboard is erased, not all DNA methylation patterns are removed. The DNA methylation makers that manage to evade the resetting process can then be passed down from parent to offspring. On top of what we inherit from our parents, we also gain and lose epigenetic marks throughout our lifetimes. Changes to the epigenome have been linked to a range of things, from diet to stress and exercise.

Diet

Our DNA methylation blueprints are laid out during gestation. As a result, an expectant mother’s diet can affect methylation patterns in the genome of her developing fetus. What’s more, during development, fetuses grow their own egg and sperm cells, building the framework for their potential children's epigenomes. In other words, an expectant mother is not just pregnant with her children, but also her grandchildren.

In general, we all need to maintain a diet rich in methyl-donating nutrients including, folate, choline, betaine, and vitamin B, throughout our lifetimes to ensure normal DNA methylation. Animal studies have shown that diets deficient in methyl before birth and during infancy result in permanent under-methylation in some regions of the genome. The agouti mouse model perfectly illustrates how a mother’s diet can directly alter the epigenome of her children.

The agouti locus controls hair color in mammals. Mice with unmethylated agouti genes have a yellow coat color, obesity, and a strong likelihood of developing diabetes and cancer. However, when a pregnant yellow dam receives a diet supplemented with methyl donors, most of her pups are born with a methylated agouti gene. If a mouse has a methylated agouti gene, it will be brown and at low disease risk. A simple tweak to an expectant mother’s diet can completely transform her children’s lives. This just goes to show how truly powerful yet impressionable the epigenome is.

Sports and Exercise

Fans have always wondered whether the world’s most elite athletes (think LeBron James, Serena Williams, Cristiano Ronaldo, or Michael Phelps) were born or made. Epigenetics complicates the situation and modifies the question. It is no longer are elite athletes made, but rather can they be made? Can large muscles gained by lifting weights or faster speed developed through interval training be passed down to children, making them better athletes?

Truth is: scientists haven’t figured that out yet. When researchers in Italy examined elite athletes, they found changes to the epigenome associated with increased muscle mass, cell size, and enhanced performance. This means that it is very likely. What scientists do know is that parents can pass on athletic experiences or training habits. 

You’ve probably heard that exercise boosts your metabolism. What you may not know is that there could be an epigenetic explanation. A study in Cell Metabolism revealed that genes involved in metabolism are demethylated or “switched on” when we workout. The amount of methylation lost depends on how intensely we work out. A different study from researchers at the Karolinska Institute in Sweden had similar results. For three months, participants exercised one leg for 45 minutes, four times a week. Biopsies of the exercised muscle revealed new methylation patterns on genes related to metabolism, insulin response, and inflammation.   

We’ve always known that exercise reduces stress, but it could also improve the way we handle stress. In a study from the University of Bristol, rats that exercised regularly showed superior coping mechanisms to unexercised rats the second time they experienced a high-stress situation. Upon further examination, the researchers found changes to epigenetic markers in the dentate gyrus, a region of the brain involved in creating memories, of the exercised rats.

Stress and Trauma

Stress can be detrimental to a person’s physical and mental health. It can lead to depression, trigger headaches, cause insomnia, weaken the immune system, and bring about a host of other issues. Still, we can learn to manage and reduce stress. The epigenetic consequences, however, can be irreversible.

Some people are naturally great at handling stress. We could easily chalk it up to luck, but it appears they were epigenetically programmed to be that way, or at least that is what some rat studies suggest. When rat moms shower their babies with love, lots of licking and grooming, the pups grow up happier and are more affectionate towards their own children. To understand why this happens, researchers from McGill University conducted a cross-fostering experiment.

They took the pups of nurturing mothers and placed them with less attentive foster moms, and vice versa. Shockingly, the scientists observed that as adults, the pups took on the traits of their foster moms and not their biological mothers. The babies adopted by affectionate mothers also grew up happier and were less stressed as adults. They even passed on these traits to their own offspring. Turns out, early affection from their mother releases hormones in the pup’s brain that lead to the methylation of some genes that control stress hormone sensitivity.

The most intense stress comes during and after traumatic events. So naturally, psychological trauma can have immediate impacts on the epigenome. One study suggests that the children of holocaust survivors have an increased likelihood of developing stress disorders. Another found lower levels of cortisol, a stress hormone, in the children of women who were pregnant during the 9/11 attacks and later developed PTSD. The children of mothers who were in the third trimester of pregnancy were the most affected.

These findings suggest that the traumas suffered by one generation can be passed down to the next. This conclusion is very premature since these were small scale studies, epigenetics is a relatively new field, and there’s still tons of research to be conducted. However, if this is true, and there is a strong possibility that it might be, it would probably be a good idea to keep an eye on all the post-pandemic babies.