Exercise May Increase Ovarian Cancer Risk

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Exercise has been shown to protect against several cancers, for instance, bowel and breast cancers and possibly endometrial and prostate cancers. Previous research on ovarian cancer has had mixed results. Obesity, especially around the waistline, can increase ovarian cancer risk, and physical activity can reduce that fat. Researchers have speculated that physical activity might help prevent ovarian cancer by regulating hormone and growth factor levels; enhancing the immune system; improving the antioxidant defense system; and reducing obesity, which increases ovarian cancer risk. However, physical activity also lowered ovarian cancer risk for women of normal weight, indicating that other factors are also at play.

A new study presented by Australian researchers in 2007 in Barcelona, Spain, suggested that exercise might actually increase the risk. Almost 25,000 Australian women between ages 27 and 75 were followed for an average of 13 years. During the study, ovarian cancer was diagnosed in 90 women. Thirteen of those women did not exercise, 21 reported low levels of physical activity, 37 reported medium levels, and 19 engaged in high levels.

After adjusting for other risk factors for ovarian cancer, the team found that women with high levels of physical activity were more likely, to develop ovarian cancer, with more than twice the risk of those engaging in no physical activity, according to Dr. Fiona Chionh from Victoria, Australia. Women with medium levels of physical activity had the second highest risk, and women with low levels of exercise also had an elevated risk, compared with those with no exercise. The results suggested there might be a dose-response effect of physical activity on ovarian cancer risk, although only the findings on medium levels of physical activity were statistically significant.

Dr. Chionh offered three possible theories supporting a link between ovarian cancer risk and physical activity. Some studies have shown that excessive levels of physical activity caused decreased estrogen levels in women. This may trigger the pituitary gland to release more gonadotropin hormones, which are thought to lead to ovarian cancer by stimulating estrogen that bring about excessive proliferation of ovarian cells.

In addition, higher levels of physical activity are related to increased androgen levels, which might play a role in the development of ovarian cancer. In other studies, higher levels of vigorous exercise led to an increased frequency of ovulation. Scientists surmised that after each ovulation, there was a proliferation and repair of ovarian cells, which led to recurrent minor trauma. Consequently, the risk of ovarian cancer might rise with more ovulatory cycles.

(Source: European Cancer Conference, September 2007, Barcelona, Spain.)

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