Moderate exercise may reduce the risk of ovarian cancer, the leading cause of gynecological cancer death.

The news comes from a Canadian study in The International Journal of Cancer's online edition.

Women weren't asked to work out. Instead, they completed surveys about their activities.

Moderate physical activity was associated with a lower risk of ovarian cancer. Vigorous exercise didn't raise or lower ovarian cancer risk, the study shows.

Ovarian cancer has few symptoms and is often diagnosed late. It has a poor prognosis because of the advanced stage of the disease at the time of diagnosis. While there are a few risk factors which increase its risk, identifying modifiable risk factors could reduce the risk of developing ovarian cancer.

Benefits of Being Active

Exercise has already been shown to guard against colon and breast cancers, say the researchers, who included Sai Yi Pan of Canada's Public Health Agency. Previous research on ovarian cancer had mixed results, they say.

Pan's study analyzed data from 442 women with ovarian cancer and 2,135 women of similar backgrounds who did not have ovarian cancer. They were 20-76 years old.

Questionnaires asked how many times per month they walked, jogged, ran, gardened, swam, skied, skated, bowled, took exercise classes, or did other activities. Age, number of children, diet, and use of alcohol and cigarettes were also noted.

Lower Risk Seen With Moderate Activity

Women who participated in the highest levels of moderate-intensity exercise had a decreased risk of ovarian cancer compared with women with lower levels of moderate intensity activity. Moderate levels of physical activity were defined as being equivalent to walking three to six times per week or golfing one or two times per week.

Decreased ovarian cancer risk was seen in women with high levels of moderate recreational physical activity before and after menopause, the study shows.

Overweight and obese women benefited a bit more than leaner women. Obesity, especially around the waistline, has been shown to increase ovarian cancer risk, and physical activity can reduce that fat. However, physical activity also lowered ovarian cancer risk for women with normal BMI, say the researchers, so other factors must come into play.

Women in Ontario also rated their activity at work. Ovarian cancer risk was also found to be lower in women with moderately active jobs.

Women with the highest levels of vigorous physical activity were not found to significantly reduce their risk of ovarian cancer.

Possible Explanations

How does physical activity help? No one is certain, but Pan outlines several possibilities.

Exercise might help the body's antioxidant and immune system defenses, combat obesity (especially around the waist), or affect hormones. Severe exercise could push the body too far, say researchers.

Reams of research have shown that activity rewards virtually the entire body, including the heart, bones, waistline, and brain.

Data Details

The study has some limits. Self-reports can be flawed. Women may have mistakenly described their activity level "moderate" instead of "vigorous," say the researchers.

The questionnaires didn't cover the length of activity sessions, so there's no word on how long a woman would have to walk, for example, to get any ovarian cancer benefit.

About 20 percent of the patients the researchers wanted to include had already died, couldn't be located, or their physicians refused to contact them about the study. Of those who were contacted, nearly one in four (24 percent) did not return the questionnaire.

"This low response rate among cases was largely due to the poor prognosis of ovarian cancer, and it could affect the generalization of our results," write researchers.

About Ovarian Cancer

Ovarian cancer is the seventh most common cancer among women (not counting skin cancer) and women's No. 4 cause of cancer death, says the American Cancer Society (ACS).

The disease often has few early symptoms. Only about a quarter of cases are found at an early stage, when the chances of successful treatment are best, says the ACS.

Recently, other researchers reported progress in developing a blood test to screen high-risk women for ovarian cancer. But that test is not yet ready for widespread use.

At-Risk Women

Any woman can develop ovarian cancer. Women at high risk (such as those with a strong family history of the disease) may be screened with ultrasound and blood tests, says the ACS.

That's all the more reason to know your family's medical history, share it with your doctor, follow screening guidelines, and ask questions about any health concerns.

Other risk factors can include never being pregnant, decreased fertility, and delayed childbearing in women who have not used oral contraceptives. Some studies have also linked the use of fertility drugs to an increased risk of ovarian cancer.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Pan, S. The International Journal of Cancer, May 16, 2005; online edition. American Cancer Society: "How Many Women Get Ovarian Cancer?" American Cancer Society: "How Is Ovarian Cancer Found?" WebMD Medical News: "Progress in Blood Test to Detect Ovarian Cancer." News release, John Wiley & Sons, Inc.