Study finds obesity a possible contributor to early menarche in girls

A recent study, conducted on over 70,000 women in the US by Harvard University's School of Public Health, discovered a correlation between early menstruation in young girls and childhood obesity. The research suggests that the average age of first menstruation has declined over the years, from 12.5 years for women born between 1950 and 1969 to 11.9 years for those born between 2000 and 2005. This trend is associated with an increased risk of adverse health outcomes such as cardiovascular disease and cancer.

The trends were found to be more stark in women belonging to racial minorities like Black, Hispanic, Asian, or mixed race and in women rating themselves as low in socioeconomic status. The study, published in The Journal of the American Medical Association (JAMA) Network Open, is the first to discern menstrual trends in women across races and social strata, according to the researchers.

“Continuing to investigate early menarche and its drivers is critical,” said corresponding author Zifan Wang, a postdoctoral research fellow at Harvard's School of Public Health.

"Early menarche is associated with higher risk of adverse health outcomes, such as cardiovascular disease and cancer,” he said.

“To address these health concerns, which our findings suggest may begin to impact more people, with disproportionate impact on already disadvantaged populations, we need much more investment in menstrual health research," Wang said.

The study revealed that it takes time for menstrual cycles to establish regularity. Among women born



between 2000 and 2005, 56 percent reported having regular periods within two years after their first period, whereas 76 percent of those born between 1950 and 1969 reported the same.

The Apple Women's Health Study gathered a varied dataset by recruiting 71,341 women from November 2018 to March 2023. About 62,000 participants reported the duration it took for their menstrual cycles to regulate, while another group disclosed their body mass index (BMI) when they had their first period.

"The mean age at menarche decreased from 12.5 years in 1950 to 1969 to 11.9 years in 2000 to 2005," the authors wrote.

"The number of individuals experiencing early menarche (before age 11 years) increased from 8.6 per cent to 15.5 per cent, the number of individuals experiencing very early menarche (before age 9) increased from 0.6 per cent to 1.4 per cent, and the number of individuals experiencing late menarche (at age 16 or later) decreased from 5.5 per cent to 1.7 per cent," they wrote.

The researchers found that BMI, an indicator of obesity, could explain the early onset of menstruation in nearly half of the women reporting that information.

"Within a subset of 9,865 participants with data on BMI at menarche, exploratory mediation analysis estimated that 46 per cent of the temporal trend in age at menarche was explained by BMI," they wrote.

The findings provide a better understanding of menstrual health across the lifespan and how our lived environment impacts this critical vital sign, said the authors.