The phenomenon is observed in girls and boys, but in girls the connection is stronger.

The results were published in the International Journal of Epidemiology and show that the onset of puberty in overweight or obese boys begins on average 3 months and in girls 5 months earlier than in normal weight.

The association was also observed in an analysis comparing children’s siblings. This suggests that the phenomenon was not explained by common habitat issues.

Overweight and obesity have been associated with premature puberty before this, but the results, especially for boys, have been unclear.

The study involved 11,000 Danish children born between 2002 and 2003, whose body mass index was determined at 7 years of age. The onset and progression of adolescence were monitored at 18 years of age.

The average menstrual age of Finnish girls is 13.3 years. In boys, puberty begins at an average age of 13.5 years.