The Who, What, Where, When and Sometimes, Why.

Age at First Period

Starting menstrual periods at a young age is linked to a small increase in breast cancer risk [10,14-18].

Women who began their periods before age 11 have about a 15-20 percent higher breast cancer risk compared to those who began their periods at age 15 or older [18].

pooled analysis of data from more than 100 studies found for every year younger a woman was when she began her periods, her breast cancer risk increased by 5 percent [16].

Age at first period, estrogen and breast cancer risk

The increased risk of breast cancer linked to a younger age at first period 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 [19].

The earlier a woman starts having periods, the longer her breast tissue is exposed to estrogens released during the menstrual cycle. This means a greater lifetime exposure to estrogen.

A woman can’t change the age when she started her period, but the age a girl starts her period can be impacted by certain healthy lifestyle factors. For example, girls who are lean and get more exercise tend to start their periods at a later age than other girls.

It’s a good idea for all young girls to be physically active and not be overweight. However, it’s not recommended girls do anything to try to change when they start getting their period.

Learn more about estrogen and breast cancer risk. 

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