The Relationship Between Physical Activity and Menstrual Cycle Characteristics

Ellen B. Gold
University of California Davis
K04ES00202

Background: Numerous studies have shown that women who exercise regularly are at decreased risk for breast cancer than women who lead a more sedentary lifestyle. However, the reasons for this difference have not been fully determined. One possible explanation could be an overall more healthy lifestyle for the women who exercise. Regular vigorous exercise can lead to longer menstrual cycles, and in extreme cases usually involving competitive athletes, missed menstrual cycles, resulting in decreased exposure of breast tissue to circulating estrogens and progesterone at various stages of the cycle. Therefore, because breast cancer is a hormonally mediated disease, these investigators investigated the role of exercise-induced changes in menstrual cycle characteristics.

Advance: Physical activity was associated with increased menstrual cycle lengths. The magnitude of this association was decreased as the body mass index increased, suggesting that the highest benefit is seen in women of normal physical stature.

Implication: The finding that more physical activity was related to longer menstrual cycles is suggestive of a mechanism or mechanisms by which exercise might reduce the risk and incidence of breast cancer. The finding also is supportive of the benefits of promoting regular, even vigorous, physical exercise. To build upon this finding, future studies should be aimed at assessing the effects of exercise on the control of hormonal feedback and reducing hormone levels.

Citation: Sternfield B, Jacobs MK, Quesenberry CP, Gold EB, and Sowers M. Physical Activity and Menstrual Cycle Characteristics in Two Prospective Cohorts. American Journal of Epidemiology. 2002 September;156(5):402-9.