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.
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.
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.