Girls’ ages at first period getting younger

Scientists found that the age of menarche (when a girl’s periods begin) has dropped in girls born in the late 1980s and 1990s, with that drop being most steep among girls of low socio-economic status. This follows several decades when girls’ ages at first period stayed the same.

Study author Danielle Morris, from The Institute of Cancer Research (ICR) in Sutton, Surrey, said: “These results suggest that girls, particularly from poorer backgrounds, are starting their periods younger. While we don’t know all the reasons behind this, changes in diet may have played a part. This decrease is important because the age at which a girl starts her periods can influence her chances of developing breast cancer later in life.”

The research uses data from over 90,000 UK women who are participating in the Breakthrough Generations Study. The study will run for 40 years, with the aim of finding the lifestyle, genetic and environmental causes of breast cancer. The number of cases of breast cancer diagnosed in the UK has risen by 50% in the past 25 years with the latest statistics showing nearly 48,000 women diagnosed with the disease in 2008. The study is a partnership between Breakthrough Breast Cancer and the ICR.

The age of menarche declined from 13.5 years for girls born at the beginning of the 20th century, to 12.6 years in those born in the 1940s. There was little change for 40 years until the age dropped again to about 12.3 years for girls born in the late 1980s onwards.

It was previously the case that girls from higher socio-economic status tended to start their periods younger. These new statistics show that the trend has reversed and girls of lower socio-economic status now start their periods at a younger age (12.1 years) than girls from wealthier backgrounds (12.5 years). Body weight is linked to the age at which a girl starts her periods. Therefore, increasing numbers of overweight children, particularly in lower socio-economic groups, could have played a part in this change.

Professor Anthony Swerdlow, from the ICR and co-leader of the Breakthrough Generations Study, says: “Incidence of breast cancer has risen progressively over a long time in the UK. We think these changes have come about through a combination of factors each of which individually makes a small difference. Understanding how these factors influence a woman’s risk of developing breast cancer should allow us to develop strategies for preventing the disease in the future.”

The Breakthrough Generations Study follows over 110,000 UK women over 40 years to help pinpoint the causes of breast cancer. Ongoing analysis costs are met in part by Marks & Spencer, through its support of Breakthrough Breast Cancer. Danielle Morris’s work was funded by the Sir John Fisher Foundation and the Institute of Cancer Research