Discovery Fit & Health
Imagine two mice sitting side by side. One is a slim, average-looking brown mouse; the other is outrageously fat, its chubby body engulfed in canary yellow fur. Now, imagine I told you that the two mice are twins -- genetically identical in every way. Would you believe me?
Odds are you wouldn’t, but that’s exactly the case in a laboratory at Duke University where researchers are studying the fascinating world of epigenetics, the genetic “software” that reads and interprets the “hardware” of DNA [source: Chaddha]. As these agouti mouse twin sisters illustrate, epigenetics can make otherwise genetically identical individuals look and act drastically differently, depending on the environment around them. In this case, it was the lifestyle (and exposure to chemicals) of their mousey mom that made the difference, but overwhelming research has recently emerged that indicates how life experiences can cause a wide range of epigenetic changes [source: Cloud].
What kind of life experiences? Well, obvious lifestyle choices like smoking and eating a poor diet are on the list but less intuitively, researchers have found that the way we’re raised plays a huge role in our epigenetic chemistry. One experiment found that rat pups who’d grown up with ample licking and coddling from their mother were able to better cope with stress once they reached adulthood due to a shift in their hippocampus chemistry [source: Weinhold]. A study of fruit flies found that even temperature can make a difference. Fruit flies raised in 37 degree Celsius (as opposed to 25 degrees) were born with red eyes instead of the standard white [source: ScienceDaily].
But perhaps the most shocking epigenetic discovery to date is that life experiences don’t just change you, they affect your children and grandchildren through generations. The isolated Swedish town of Norrbotten once dealt with years of severe famine followed by abrupt seasons of abundance. In the 1980s, Dr. Lars Olov Bygren did a now-seminal study of the population’s health and how it related to these alternating times of feasting and starvation. What he found was that if parents or grandparents transitioned from being starved to overeating in a season, their children and grandchildren led significantly shorter lives (by nearly six years, on average) [source: Cloud]. These children were also at higher risk for cardiovascular disease and diabetes well into adulthood [source: Hunter].
But remember, the door swings both ways: If exposure to chemicals, overeating, and other lifestyle choices can encourage illness, then eating right and being aware of your surroundings can help prevent it. In the agouti mouse study, the key to slim, healthy babies was simply a change of diet. (In their case, eating onions, garlic and beets) [source: Watters].
Though research is still ongoing when it comes to specific actions, living a generally healthy life still appears to be the best course of action. Randy Jirtle, the geneticist behind the epigenetic mouse study, had this to offer: “My mother told me repeatedly when I was a kid to eat my vegetables and make sure I always ate breakfast. This seems to me to still be sound advice” [source: Jirtle].
Life experiences are believed to cause epigenetic changes, meaning that your behavior and experiences could produce responses in your body that, while they don't change DNA, change which genes are expressed. Usually this occurs when, in response to stimuli (say, an increase in a certain hormone), a cluster of molecules known as a methyl group attaches to a section of DNA, preventing that bit of DNA from expressing a particular gene. The "silenced" gene then won't produce its associated protein. Known as DNA methylation, this process may also contribute to the development of some cancers, with certain genes being turned on and, consequently, leading to uncontrolled cell division.
The role of stress in human health and the epigenome lately have received particular scrutiny. Research has found that glucocorticoids, which are so-called "stress hormones," change gene expression in the brain. This is not necessarily a bad thing. One Johns Hopkins researcher, when speaking to the National Institutes of Health, suggested that epigenetic changes might prepare the body to cope with future stressful encounters [source: Johns Hopkins Medicine]. On the other hand, understanding these epigenetic changes could help in treating depression, post-traumatic stress syndrome, bipolar disorder and other illnesses associated with stress.
Childhood exposure to intoxicants may also produce epigenetic changes. These changes may then lead to diseases and complications much later in life. But say you're exposed in childhood to a toxic chemical, which leads to epigenetic changes. It turns out these changes may not only affect you. In October 2010, Newsweek reported on the work of Michael Skinner, a researcher who published a paper arguing that a person's epigenetic changes can be passed down not only to that person's children but also to the person's grandchildren. Consequently, a man exposed to harmful substances may pass on certain gene expressions that produce abnormalities in the organs of his children.
Despite these findings, the relationship between epigenetics and life experiences remains a new field. Although many behavioral scientists are excited at the possibilities, some critics have charged that researchers seem to be announcing results prematurely. Specifically, skeptics worry that some behavioral scientists make premature correlations between a small piece of methylated DNA and a possibly associated behavior, without fully understanding the biological mechanisms that may be at work.(Photo courtesy U.S. DOE, Human Genome Project)
The field of epigenetics is relatively new, but already, research studies are revealing significant proof that epigenetic changes -- brought on by life experiences -- do occur. Perhaps one of the most compelling links between experiences and epigenetic changes has involved the link between parental affection at a young age and the ability to cope with stress later in life. Researchers have conducted tests on lab rats that show that those rats that received plenty of loving licks from their mom rats as pups coped better in stressful situations as mature rats.
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