Studies have found the onset of puberty is earlier than before for many girls, putting them at risks of health issues such as high stress and behavior problems. A team of researchers from the United Kingdom recently put forward evidence suggesting the earlier girls start their period, the higher the risk of becoming overweight as adults. 

The paper titled “Age at Menarche and Adult Body Mass Index: a Mendelian Randomization Study” was published Feb. 26, 2018, in the International Journal of Obesity. Researchers from the Imperial College London studied data collected from a large number of women, using genetic variants as tools, to show the link between early onset of puberty and increased body mass index.

“Previous studies have shown there is an association, but we didn't know whether early puberty caused obesity in adulthood, or was simply associated with it. In our latest study we've generated evidence to support that it is a causal effect,” said Dr. Dipender Gill from the Imperial College in London.

Single “letter” changes to the DNA sequence of genes, inherited from parents, can increase or decrease the risk of diseases. Combinations of these variants involving more than 20,000 genes are what contribute towards cumulative genetic risk.

"Some of these genetic variants are associated with earlier puberty and some with later onset, so by taking advantage of this, we were able to investigate any association of age at menarche with BMI in adulthood," Dr. Gill explained.

Researchers employed a statistical technique called “Mendelian Randomization,” which uses measured variation in genes to obtain unbiased estimates of the effects of a variable. The study examined data from 182,416 women and identified 122 genetic variants that were strongly associated with the onset of puberty. The participants used a questionnaire to reveal the age at which they had their first period, known as age at menarche.

The U.K. biobank was also used to examine another 80,465 women, where the ones who had variants associated with early puberty also had an increased body mass index (BMI). A similar association was also found in a third group made up of 70,962 women from The Genetic Investigation of Anthropometric Traits consortium.

The study concluded the evidence was strong to suggest an earlier age at menarche could cause higher adult BMI, owing to "complex hormonal and psychological factors." Data also showed a one-year delay in puberty was associated with a 0.38kg/m² reduction in adult BMI. 

"It is difficult to say that changing someone’s age of puberty will affect their adult risk of obesity and whether it is something that we can clinically apply — as it would unlikely be ethically appropriate to accelerate or delay the rate of puberty to affect BMI," Dr. Gill added. "But it is useful for us to be aware that it’s a causal factor — girls who reach puberty earlier may be more likely to be overweight when they are older."