This is shown by a new study from Aarhus University, which has analyzed height, weight, and puberty data from nearly 13,000 Danish children.

“Overall, we found that children who entered puberty early had a higher BMI before, during, and after puberty,” explains postdoc Anne Gaml-Sørensen from the Department of Public Health.

“However, we were surprised to see that the connection between early puberty and higher BMI in adulthood, which other studies have shown for boys, can partly be explained by the fact that they already had a higher BMI before puberty,” continues Anne Gaml-Sørensen.

Unique opportunity to follow children closely

The study is based on the cohort “Better Health in Generations” (BSIG), where researchers have linked information about pubertal development with more than 136,000 height and weight measurements from school and medical records, among others.

The children were followed closely from ages 7 to 18 — a method that differs significantly from previous research in this area.

Most previous studies have been limited to a single BMI measurement and a single marker for puberty, such as age at menarche. This has made it difficult to say anything definitive about how weight and pubertal development are connected over time.

“What makes our study unique is that we can track BMI and pubertal development over several years. We have many different puberty milestones, and we can compare them with BMI at many points in childhood and adolescence,” explains Professor Cecilia Høst Ramlau-Hansen, who has researched pubertal development for more than ten years and is another of the main authors of the study.

Biological differences between the sexes

The results show that girls with early puberty have higher BMI as young adults — even if they had normal weight in childhood.

This suggests that there is a biological difference between the sexes that makes girls more vulnerable to the impact of early puberty on weight.

For boys, there was only a small independent effect of puberty age when researchers accounted for their BMI as seven-year-olds. Their development therefore more closely follows the pattern one would expect based on their weight in childhood.

“We see the strongest signal in girls, and this may well be due to a real biological difference between the sexes. It is possible that the hormonal changes that girls undergo during puberty have a greater effect on the body’s fat storage and metabolism — and thus increase the risk of overweight later in life,” says Associate Professor Nis Brix, who is also one of the main authors of the study.

“At its core, it’s important that school nurses and other professionals are aware that earlier puberty appears to increase the risk that especially girls have a higher BMI throughout adolescence and as young adults,” says Anne Gaml-Sørensen.

However, the researchers emphasize that these are small differences, so it should not cause concern for individuals.