Age at menarche (when periods begin) is known to run in families. However, the balance of genetic and environmental influences on this has been unclear.
Scientists at The Institute of Cancer Research (ICR) analysed data from women participating in the Breakthrough Generations Study - a major UK-wide investigation into the causes of breast cancer - who had at least one other female relative also taking part. They found that a woman’s age of menarche was significantly correlated with that of her relatives. For each 12 month delay in age at menarche of an older sister, mother or paternal aunt, there was a delay of around three months on average for the younger relative; and for a maternal grandmother or maternal aunt the delay in the younger relative was about 1.5 months. Age at menarche also strongly correlated between twins, particularly identical twins. The researchers used mathematical modelling to find that genetic factors accounted for around 57 per cent of the variation in the age of menarche of women in the study.
Environmental and behavioural factors from sharing an upbringing or family life did not appear to have any detectable effect; environmental factors not shared within families accounted for the other 43 per cent in variation. The age at which menstruation begins is important because it has been linked to risk of a number of chronic diseases including breast cancer. Risk of breast cancer gradually increases with progressively younger age at menarche and older age at menopause, possibly because women are exposed to female sex hormones for a longer period of time. Each two year delay in menarche is associated with an estimated 10 per cent reduction in the relative risk of breast cancer. Our study findings suggest that genetic factors have a major influence on the age women in the UK begin menstruating, and these could have an impact on breast cancer risk,” lead author Danielle Morris of the ICR says. “ Although some genes associated with age at menarche have been found, considerable genetic variation remains to be explained.” The Breakthrough Generations Study is a comprehensive analysis of the causes of breast cancer.
A partnership between Breakthrough Breast Cancer and the ICR, it began in 2003 and will follow more than 100,000 women participants for the next 40 years to unravel the lifestyle, environmental and genetic factors that cause the disease This arm of the study was funded by Breakthrough Breast Cancer, the ICR and the Sir John Fisher Foundation. The study analysis is funded by M&S, and Walk the Walk support the study and scientific team.