The researchers examined data on puberty timing and any experiences with bullying among 227,443 teen girls in 35 countries. Slightly more than 4% of the girls started menstruating early, defined in the study as before age 11.
Early menstruation was associated with 21% higher odds that girls would be occasional victims of bullying and a 35% greater chance of frequent victimisation.
At the same time, teens who started menstruating sooner than most other girls were 19% more likely to occasionally bully other students at school and had 46% higher odds of becoming frequent bullies.
“This study emphasises how intricate and complicated peer relationships can be during early adolescence, particularly for kids whose physical development puts them out of sync with their peers,” said Jane Mendle, a human development researcher at Cornell University in Ithaca, New York, who wasn’t involved in the study.
“Peers are so important during early adolescence, especially for girls,” Mendle said by email. “Maturing early can contribute to kids feeling different from others in their grade at school, and it can also make kids stand out.”
While few previous studies have examined the link between bullying and puberty timing, early maturation has long been linked to an increased risk of conflict with other kids, feeling different and isolated, and being the victim of peer sexual harassment, Mendle added.
Puberty usually starts between the ages of 8 and 13 years old in girls. Breast and pubic hair development usually come first, followed about two years later by the start of menstruation.
Children who go through early puberty may be shorter than average adults because their bones may stop growing at a younger age, and they are also at increased risk of obesity as adults. During adolescence, they may face an increased risk of social and emotional problems and earlier sexual experiences.
Some recent research points to earlier puberty onset in the general population, especially in girls in developed countries. Environmental factors like diet, obesity, and chemicals that mimic human hormones have all been suspected of playing a role.
The current study examined survey data collected in four waves from 2001 to 2010 in 32 European countries, as well as Canada, Israel, and the US. During the study period, early menstruation became a little more common and the proportion of girls involved in bullying declined slightly.
By the end of the study, roughly 31% of girls who started menstruation early were either victims or perpetrators of occasional bullying, compared with about 26% of girls who started menstruating at age 12 or later.
The trend was similar with frequent bullying. In the last survey wave, about 11% of girls who started menstruating early were regularly victims of bullying and more than 9% were often bullies, compared with about 8% and 7%, respectively, of girls who began menstruating later.
One limitation of the study is that researchers relied on girls to accurately recall and report on the timing of menstruation and their experiences with bullying, the authors note in Journal of Adolescent Health.
Researchers also relied on girls to report their own weight, which might give an accurate picture of the proportion of overweight and obese girls in the study. Obesity is independently linked to both early puberty and bullying.