Researchers aren’t sure how early onset of puberty impacts body weight, but they think it might be due to the physical effects of hormonal changes, leading fat to be deposited in other parts of the body.
Girls who start their periods at an early age have a higher risk of being overweight as adults, a new study claims.
Previous studies established a link between obesity and puberty, with increased body weight known to be a risk factor for girls starting puberty earlier.
However, the new study, led by researchers at Imperial College London, suggests early onset of puberty is itself a risk factor for being overweight.
Researchers found that early onset of puberty may be a risk factor for obesity
The average age girls start menstruating is 12, but about one-third of American girls are now entering puberty by the age of eight.
Dr Dipender Gill, lead author of the study, said the new research untangle external factors, such as economic background, diet and education, to find an causal link between early puberty and a woman’s risk of obesity.
‘Our study provides more insight as opposed to earlier studies because we show that early puberty causes obesity and not just that there’s an association,’ Dr Gill, a Wellcome Trust Clinical Fellow at Imperial College London, told Daily Mail Online.
For the study, researchers looked at genetic variants that are associated with early puberty.
‘We looked at genes that were proxy instruments to early puberty,’ he said. ‘These genes are randomly gifted to use from out parents… one form of a gene can cause women to get their period earlier while another can cause women to have puberty later in life.’
Using data from 182,416 women, the researchers identified 122 genetic variants that were strongly associated with the onset of puberty – with the women’s age at first period obtained via questionnaire.
They then looked at data collected from a second set of 80,465 women to see how early puberty impacted adult BMI.
They found that people who started their puberty earlier, before the average age of 12, were more likely to be obese than those who started their period later.
In fact, they found that a one year delay in puberty was associated with a 0.38kg/m² reduction in adult BMI.
Researchers then tested for this same association in a third group of 70,962 women and found the same link.
‘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 which a girl got her first period with BMI in adulthood,’ Dr Gill said.
Previous studies have linked early onset of puberty to adverse health outcomes.
A 2009 study published in the journal Trends in Endocrinology Metabolism found early onset of puberty was linked to obesity, type 2 diabetes and breast cancer in young girls.
Another study published earlier this year in the journal Heart found girls who start menstruating before they turned 12 years old had a greater risk of developing heart disease or having a stroke later in life.
Researchers of the current study said it remains unclear how maturing earlier has a direct impact on body weight, but they believe that differences between physical and emotional maturity may play a role.
They also believe body changes associated with puberty may be a factor, such as increased fat deposition in breast tissue, hips and thighs, which when established earlier can put them at risk of becoming obese 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,’ Dr Gill said.
However, with more research, he said doctors may be able to minimize the negative affects associated with early puberty.