Breakthrough Generations study data reveals factors behind age at which girls start their periods

Research using data from the Breakthrough Generations Study has shown a wide range of factors – some beginning before a child is born – affect the age at which a girl starts her periods.

Age at menarche (when periods begin) has long been established as a risk factor for breast cancer. Risk of the disease gradually increases with younger age at menarche and older age at menopause.

Using data from participants in the Breakthrough Generations Study, the results show that girls who were heavier and exercised less often were more likely to have an early menarche.

Other factors that are related to early menarche identified by the study team included girls who were not breast fed, had a low birth weight and were taller.

Analysis leader, Danielle Morris, said “A girl who takes more exercise is likely to start her periods later in life. We know exercising regularly as an adult can help reduce the risk of developing breast cancer. This study shows that exercising as a child could also potentially have an effect on breast cancer risk later in life.”

In another paper, the Study found that the age at first period (menarche) decreased by about a year when comparing Generations Study members born at the beginning of the 20th century and those born in the 1940s. Although there was little change between most generations born after the Second World War, the age decreased again for the youngest Generations Study members, born in the late 1980s and early 1990s. Interestingly, although in Victorian times, and also for the oldest members of the Generations Study, women from better-off families started their periods earlier than women who were poorer, the opposite is now true for the youngest study members – poorer girls now have their menarche younger than better-off ones.