Exercise and the Prevention of Breast Cancer

Institution: University of Southern California
Investigator(s): Lisa Shames, Ph.D., M.P.H. -
Award Cycle: 1995 (Cycle I) Grant #: 1KB-0060 Award: $367,464
Award Type: New Investigator Awards
Research Priorities
Etiology and Prevention>Prevention and Risk Reduction: ending the danger of breast cancer



Initial Award Abstract (1995)
There is substantial evidence to suggest that estrogens play a key role in the biological cause of breast cancer. We recently observed in a large population-based study that exercise, including moderate exercise, may significantly reduce a woman's risk of breast cancer. We hypothesize that the reduction in risk with exercise is due to altered ovarian function, specifically, more frequent anovulatory cycles (i.e., a menstrual cycle without release of an ovum) and/or reduced serum estrogen (and progesterone) levels in ovulatory cycles which likely contribute to a reduced exposure of breast tissue to estrogen and thus reduce the risk of breast cancer. Studies of highly trained athletes show that women who engage in exercise for close to an hour or more per day have a higher frequency of anovulation, lower levels of estradiol (E2 -- the most active form of estrogen) and, in some cases, a shortened luteal phase length with associated lower estradiol levels.

The purpose of this study is to investigate the relationship between exercise and ovarian function across a range of physical exercise activity that non-athletes may reasonably be expected to participate in (i.e., sedentary to less than an hour per day). Specifically we will aim to: 1) determine the relationship between physical exercise activity and frequency of anovulation, 2) determine pre- and post-ovulatory cycle lengths of women exercising at these various levels, and 3) measure serum hormone levels of E2 in these women. We plan to study 300 college students between the ages of 18 and 25 years, who have never borne children, over 2 complete menstrual cycles. A questionnaire consisting of demographic information, exercise, diet and medical history will be administered.

This study should contribute significantly to our understanding of the relationship between physical exercise activity and ovarian function. With this relationship better understood, it would be possible to provide readily understandable, practical advice to women on how to reduce their breast cancer risk through physical exercise activities.


Final Report (1999)
There is substantial evidence to suggest that estrogens and progesterone play a key role in the etiology of breast cancer. We observed in a large population-based case-control study, that exercise, including moderate exercise, may significantly reduce a woman's risk of breast cancer. It was hypothesized that this may be due to exercise producing lower serum estrogen and progesterone levels. Studies of highly trained athletes show that such women have a higher frequency of anovulation, lower levels of estradiol (the most active form of estrogen) and progesterone, and in some cases a shortened luteal phase length with associated lower total estradiol and progesterone exposure. The aim of this study was to investigate the relationship of exercise to ovarian function across a range of exercise activity that non-athletes may reasonably be expected to participate in (i.e., moderate exercise). Specifically, our aims were: 1) to determine the relationship between level of exercise activity and frequency of ovulation; 2) to determine the relationship between level of exercise activity and follicular and luteal serum levels of estradiol (E2) and progesterone (Prg) in the subgroup of these women who were ovulating; and 3) to determine the luteal phase menstrual cycle lengths in these women by determining the day of ovulation through measurement of daily urinary luteinizing hormone (LH).

We studied 240 nulliparous college students between the ages of 18 and 35 years, over 2 complete menstrual cycles. A questionnaire consisting of demographic information, exercise, diet and medical history was also administered. Serum and urine samples were collected. We have found no evidence of any effect of moderate exercise on frequency of ovulation, serum E2 and Prg levels, or cycle length. Because we found no effect of exercise on cycle length we have not pursued Aim 3 to the extent of making LH determinations. Aim 3 is assumed to be answered. These results strongly suggest that if such moderate exercise is in fact protective against breast cancer it must be acting via another pathway, e.g. possibly through insulin-like growth factor - we will be pursuing such ideas further using the serum collected in this study.

Ethnic Differences in ovulatory function in nulliparous women.
Periodical:British Journal of Cancer
Index Medicus: Br J Cancer
Authors: Haiman CA, Pike MC, Berstein L, Jaque SV, Stanczyk FZ, Afghani A, Peters RK, Wan, Shames L
Yr: 2002 Vol: 86 Nbr: 3 Abs: Pg:367-371