Girls who start puberty earlier are more likely to be overweight as adults, according to scientists, including one of Indian origin.
The findings, published in the International Journal of Obesity, strengthen existing evidence of a link between the onset of puberty and a woman's body mass in adulthood.
The study showed 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 researchers, 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.
"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 Dipender Gill from Imperial College London in the UK.
In order to get around the effects of confounding factors, the scientists 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.
For the study, researchers employed a statistical technique called Mendelian Randomisation which uses these genetic variants as a tool to show the causal relationship between earlier puberty and increased BMI.
They examined 182,416 women and identified 122 genetic variants that were strongly associated with the onset of puberty - with the women's age at first period obtained via questionnaire.
The researchers then looked at data from the UK Biobank, which holds biomedical information on hundreds of thousands of people.
Specifically, they looked for the effect of the genetic variants related to age at menarche with BMI in a second set of 80,465 women from the UK Biobank, for whom they also had measurements for BMI.
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.
"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," Gill said.
"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," he said.
"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," Gill added.
