Girls who start puberty earlier could be at an increased risk of obesity

New UK research has found that starting puberty early is a risk factor for women becoming obese in later life, with girls who have their first period earlier more likely to have a higher Body Mass Index (BMI) in adulthood.

Previous research has already found a link between early onset of puberty and BMI later in life, with increased body weight also known to be a risk factor for girls starting puberty earlier.

However, as these findings have been observational they are also at risk of being influenced by situational factors, such as ethnicity, economic background, education level, and diet, making it difficult to determine whether it is early puberty or other factors that are the cause of adult 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,” explained first author of the study Dr Dipender Gill. “In our latest study we’ve generated evidence to support that it is a causal effect.”

Carried out by Imperial College London, the study was able to determine early puberty as a causal factor by using genetic variants to look at the effect of the onset of puberty (measured as being the age of a girl’s first period) on BMI later in life.

Using data from 182 416 women, the team identified 122 genetic variants that were strongly associated with the onset of puberty, and collected data on the women’s age at first period.

AFP/File / Vanderlei Almeida People with a BMI (body weight index, a ratio of weight to height) of 25 and higher are classified as overweight, and 30 and over obese

They then looked at data from a second set of 80 465 women, for whom they also had measurements for BMI, to assess the effect of the genetic variants related to the onset of puberty on BMI.

The results showed that there was a link between the genetic variants and BMI, with women who had the variants associated with earlier puberty also having an increased BMI.

To check their findings, the team tested the association again in a third group of 70 962 women, which revealed the same results.

The team noted that the genetic variants could be influencing body weight in ways independent of early puberty, for example by altering metabolism or fat production. However, even after taking into account genetic variants that were also associated with childhood obesity the findings were still the same.

Although it is still unclear how early puberty influences BMI in adulthood, the researchers suggested that girls who mature physically earlier than their peers may have different pressures put on them by society.

Alternatively, hormonal changes that occur during puberty could put girls at a higher risk of a high BMI 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 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.”

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