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Home > Understanding Breast Cancer > Risk Factors and Prevention > Reproductive Risks > Age at First Period


Age at First Period


How Hormones Affect Breast Cancer
Fact Sheet

Starting menstrual periods at a young age is linked to a small increase in breast cancer risk [6,13-17]. Women who began their periods before age 12 have about a 20 percent higher risk compared to those who began their periods after age 14 [15]. A large pooled analysis of data from more than 100 studies found that for every year younger a woman was when she began her periods, her breast cancer risk increased by five percent [13].

This increased risk is likely due, at least in part, to the amount of estrogen a woman is exposed to in her life. A higher lifetime exposure to estrogen is linked to an increase in breast cancer risk [18]. The earlier a woman starts having periods, the longer her breast tissue is exposed to estrogens released during the menstrual cycle and the greater her lifetime exposure to estrogen.

Learn more about estrogen and breast cancer risk.

A woman cannot change the age when she started her periods. However, the age a girl starts getting her period can be impacted by certain healthy lifestyle factors. For example, girls who are lean and get more exercise tend to start periods at a later age than other girls. It is a good idea for all young girls to be physically active and not be overweight. However, it is not recommended that girls do anything to try to change their natural age at menstruation.

Updated 12/11/13  


Age at First Childbirth and Number of Childbirths  

  Age at Menopause