Early puberty linked with increased risk of obesity for women

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Girls who start puberty earlier are more likely to be overweight as adults, a study has found.

Researchers at Imperial College London said their findings strengthen existing evidence of a link between the onset of puberty and a woman’s body mass in adulthood.

They said their research shows early puberty is a risk factor for being overweight, with girls who have their first period earlier more likely to have a higher Body Mass Index (BMI).

The observational findings from other studies can be influenced by situational factors such as ethnicity, economic background, education level and diet, making it difficult to determine whether early puberty or these other factors are the cause.

In order to get around this, the team used genetic variants as a tool to look at the effect of the onset of puberty, measured as the age of a girl’s first period.

They said the link between early puberty and being overweight is not genetic – but using genetic variants simply meant they could dismiss these external factors.

Researchers said it remains unclear how maturing earlier has a direct impact on body weight, but 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.

“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.”

In their study, which is published in the International Journal of Obesity, the team 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.

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 a questionnaire.

The team then looked at data relating to 80,465 women from the UK Biobank, which holds biomedical information on hundreds of thousands of people, analysing the effect of genetic variants relating to age at onset of puberty, and 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 of 70,962 women, finding the same association.

Dr Gill added: “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.

“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.”

Previous research from the group has used the same technique to show that low iron levels are associated with an increased risk of heart disease, as well as showing that girls who start puberty earlier are likely to spend less time in education.

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