Early puberty may result in obesity for women

London [U.K.]: Turns out, early puberty is linked to the increased risk of obesity for women.

According to a study led by the Imperial College London, girls who start puberty earlier are more likely to be overweight as adults.

The researchers say their findings strengthen existing evidence of a link between the onset of puberty and a woman's body mass in adulthood.

Previous studies have established a link between obesity and puberty, with increased bodyweight known to be a risk factor for girls starting puberty earlier.

But now this latest research shows that early puberty is itself a risk factor for being overweight, with girls who have their first period earlier more likely to have a higher Body Mass Index (BMI).

According to the authors of the study, their findings help to untangle these complex external factors and add insight into an underlying causal link, showing that early puberty has a significant impact on a woman's risk of obesity.

Dr Dipender Gill, the first author of the study, said: "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."

In order to get around the effects of confounding factors, the research team used genetic variants as a tool to look at the effect of the onset of puberty (known as age at menarche), measured as the age of a girl's first period.

In the latest study, researchers employed a statistical technique called Mendelian Randomization which uses these genetic variants as a tool to show the causal relationship between earlier puberty and increased BMI.

Using data from 182,416 women they identified 122 genetic variants that were strongly associated with the onset of puberty - with the women's age at first period obtained via questionnaire.

Initial analysis revealed a link between these genetic variants and BMI, with those women who had variants associated with earlier puberty having an increased BMI. The researchers then tested for this same association in a third group 70,962 women, finding the same association.

Dr Gill, added, "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".

"We're not saying that it's a genetic effect, but rather that by using these genetic variants as a proxy for earlier puberty, we are able to show the effect of earlier puberty without the impact of external factors that might confound our analysis. We performed a range of statistical sensitivity analyses to test the robustness of our findings and they remained strong through this, so within the limitations of the study design, we are confident of findings."

According to the researchers, it remains unclear how maturing earlier has a direct impact on body weight, but they indicate that differences between physical and emotional maturity may play a role. It could be that young women who mature earlier than their peers are treated differently or have different societal pressures than girls of the same age who have not started puberty.

Another explanation could be the physical effects of hormonal changes during puberty, such as increased fat deposition in breast tissue, which when established earlier may move them to a higher risk profile for higher BMI or obesity in later life.

"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," added Dr Gill. "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."

The findings from this study are published in the International Journal of Obesity.