Published by Paul Enck and Nicole Simon
This is part 33 of a series covering twin health provided by Paul Enck from the Tübingen University Hospital and science writer Nicole Simon. Further studies in twin research can be found at TwinHealth website. Translation was done with the assistance of DeepL translator.
In a previous posting, we have shown that from childhood to adolescence, the influence of genes increases — but what about when you grow older? Scientists now demonstrate that this trend may be reversed.
Uncontrolled, undisciplined and lazy — these are common prejudices against obese people. Overweight people are often blamed for their own body fullness. But there is some evidence that our weight is to a large extent also genetically determined. Scientists today assume that 57 to 90 percent of the fluctuations in the BMI of adults can be explained by genes.
The fact that there is no more precise figure here and that the results in studies have always differed may also be due to the fact that the influence of genes in East Asia is different from that in Europe, or that it changes over the course of a person’s life. It may also make a difference whether women or men are examined. To find out exactly this, dozens of scientists around Karri Silventoinen from the University of Helsinki have now investigated what influence factors such as gender, age, and the region in which one lives have on heredity. Their conclusion: age has a particularly large influence.
For the study recently published in the American Journal of Clinical Nutrition (1), the researchers analyzed data from over 140,000 twins from more than 20 countries. The researchers divided the participants into the geographical regions Europe, North America, Australia, and East Asia. All participants were at least 20 years old and none of them suffered from diseases such as anorexia or severe obesity.
For both women and men, the average BMI of subjects aged increased between 20 and 29 years and decreased again between 60 and 69 years. The scientists were particularly interested in twin pairs in which one twin was overweight and the other was not — so-called discordant twins in one trait. When the scientists looked at which factors might be responsible for these differences in the BMI of their test persons, they came across genetic effects, in particular, the individual effects of which add up. However, environmental factors that the two twins do not share also seem to be important. These could be experiences at school, at work, or in a relationship with another person.
However, the estimated hereditability of BMI differences was not the same at all times. It diminished over the years. The researchers assume that genetic factors lose weight over time, while individual environmental factors become increasingly important. There also seems to be a difference between men and women.
“We found clear evidence that different groups of genes influence the BMI of men and women,” the researchers write in their paper.
The differences are already apparent in early childhood but are becoming increasingly important in adolescence. This could be related to hormonal changes during puberty, which causes men and women to develop their bodies differently. The researchers, however, found no major differences when they compared the influence of genes in different geographical regions. Even if the BMI changed particularly strongly in certain regions — the largest differences in the BMI were measured by the scientists in North America and Australia — the influence of the genes seems to remain the same.
- Silventoinen K et al. Differences in genetic and environmental variation in adult BMI by sex, age, time period, and region: an individual-based pooled analysis of 40 twin cohorts. Am J Clin Nutr. 2017;106(2):457-466.