Girls who start puberty earlier are more likely to be overweight as adults.
A study, to be published today in the International Journal of Obesity, shows that early puberty is a risk factor for being overweight.
Previous studies have established a link between obesity and puberty, with increased bodyweight known to be a risk factor for girls who start puberty earlier.
However, it was not clear whether the findings could have been influenced by situational factors, such as ethnicity, economic background, educational level, and diet.
Imperial College London researchers used genetic variants as a tool to show the causal relationship between earlier puberty and increased body mass index.
“In our latest study, we’ve generated evidence to support that it [early puberty] is a causal effect,” said lead researcher Dipender Gill.
Using data from 182,416 women, the researchers identified 122 genetic variants that were strongly associated with the onset of puberty.
The women’s age at first period was obtained from a questionnaire.
The team then looked at data from the UK Biobank, which holds biomedical information on hundreds of thousands of people
They used the biobank to examine a further 80,465 women, for whom they also had BMI measurements.
Their initial analysis showed a link between the genetic variants and BMI. Women who had variants associated with early puberty had an increased BMI.
The same association was also found in a third group, of 70,962 women.
“We’re not saying that it’s a genetic effect, but, rather, 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,” said Dr Gill.
The researchers performed a range of statistical sensitivity analyses to test their findings and they remained strong.
However, it remains unclear how maturing earlier impacts body weight, but differences between physical and emotional maturity may play a role. It may be that girls who mature earlier than their peers are treated differently or face different societal pressures than girls of the same age who have not started puberty.
Another explanation may 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 later in 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 be unlikely to be ethically appropriate to accelerate or delay the rate of puberty to affect BMI,” said 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 group have used the same statistical technique, called Mendelian Randomization, to show that girls who start puberty earlier are likely to spend less time in education and that low iron levels are associated with an increased heart-disease risk.
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