If it could be scientifically proven that regular exercise staves off common, life-shortening diseases despite your genetic make-up, would you feel differently about exercise? We’re not quite there yet, but we are getting closer.
The difficulty in trying to determine how exercise affects our risks of developing common diseases like heart disease and diabetes is that it is hard to conduct long-term clinical trials that definitively link exercise (or lack thereof) to diseases contracted later in life. The most obvious problem is, even if one could design a study with a large, randomized amount of participants, including a control group, in proving there is a difference in disease development over time between those who exercise and those who don’t, one wouldn’t know how much differences in genetics, diet and other environmental factors contributed to disease contraction regardless of exercise.
This conundrum is precisely why it’s invaluable to enlist identical twins in studies such as these. Identical twins have the same DNA and grew up in the same household which means they lived under the same socio-economic conditions, eating the same diet and experiencing the same environmental factors in their formative years.
Thus far, identical twin studies have indicated that, at end of life, those twins who exercised more throughout life than their twin siblings tended to live longer and contract fewer diseases. It’s promising information in linking more exercise to longer, healthier lives. But it’s not perfect. Because, while it’s true that these studies control for DNA, they can’t control for other factors that can diverge for twins after they leave the same household. For example, their diets can become very different after decades living apart, they may be living under different socio-economic conditions, they could be exposed to different pollutants or experience different stress factors due to variances in occupations or relationship issues.
But a new study on identical twins suggests that exercise does make a huge difference on risk factors for diseases linked to mortality. This study from Finland, using the FinnTwin16 database, has been collecting data from identical twins beginning at the age of 16. This is the first large identical twin study that begins at such a young age and follows them as they age.
Not surprisingly, many identical twins remain very similar in lifestyle factors, such as diet make-up and exercise frequency, even after they enter adulthood, leave home and lead separate lives. However, the study was able to identify 10 sets of twin males who did differ greatly in exercise frequency by the time they reached their early to mid-twenties. In all ten cases, one twin exercised regularly while their counterpart didn’t exercise. In all cases, both siblings were exercising regularly when the study began, at the age of 16, but one twin had stopped exercising (usually due to work or family obligations) within the last three years. Also, in all cases, diets remained very similar. Metabolic and fitness tests, as well as brain scans, were conducted on all 20 individuals and the results were startling.
Those who were sedentary had a higher body fat percentage, indications of insulin resistance (an early risk factor for diabetes and other metabolic conditions), inferior cardiovascular capabilities and far less grey matter (especially in the parts of the brain that control motor function and coordination) compared to their active brothers. Considering that these dramatic differences in health indicators occurred after only a few years of a sedentary lifestyle, imagine how different the health of each twin would be compared to his brother over a lifetime.
Getting back to my original question, this isn’t proof that you can overcome a genetic predisposition to common diseases by exercising. This is not a clinical study, which uses a randomized sampling in a controlled testing environment. It is an epidemiological study that relies on questionnaires and surveys to collect data on individuals which can lead to subjective influences on the data and the sample for this study is small and not randomized. However, because the participants are identical twins, this study does offer something that most epidemiological studies can’t, and that is it does control for very important variables, the most important one being DNA. And the results in this study are consistent with other epidemiological and clinical exercise studies that have been conducted on identical twins as well as randomized studies on general populations.
Where this study may lack in proof of causation, I believe, it makes up for in hope. Many studies indicate there is a relationship between frequency of exercise and disease risk. What this study seems to suggest is the relationship exists no matter our DNA. That it isn’t rational to have a fatalistic attitude over bad genes. For me, that means hope informed by science that I have a lot more control over my health than I once thought. I hope, after reading this, you feel that way too.
Click here to read The New York Times article on this study.