Among women who have never used postmenopausal hormones, those who are obese are almost twice as likely to develop ovarian cancer as those who are a healthy weight. These results were published in the journal Cancer.
Ovarian cancer is the fifth leading cause of cancer death among U.S. women, with a projected 21,650 new cases and 15,520 deaths in the year 2008.
Although the causes of ovarian cancer are still not well understood, it is believed that full-term pregnancies and the use of oral contraceptives decrease risk, while a family history of the disease increases risk. Studies have also suggested that postmenopausal hormone use may increase risk.
Being overweight or obese has been linked with an increased risk of several types of cancer (such as endometrial cancer, postmenopausal breast cancer, and colon cancer), but the relationship between body weight and risk of ovarian cancer remains inconclusive.
One way in which excess body weight may contribute to ovarian cancer is through estrogen production. After menopause, when estrogen production by the ovaries drops dramatically, estrogen continues to be produced in fat tissue; overweight women therefore tend to have higher circulating levels of estrogen than healthy-weight women after menopause.
If obesity does in fact influence ovarian cancer risk by raising estrogen levels, this effect should be most apparent among women who have never used postmenopausal hormones (estrogen alone or estrogen plus progestin). Obesity may have less of an effect on ovarian cancer risk among women who have used postmenopausal hormones because these women would already have elevated estrogen levels as a result of their hormonal therapy.
A commonly used (though imperfect) measure of body size is the body mass index (BMI). BMI involves a comparison of weight to height (weight in kilograms divided by height in meters squared). A BMI between 18.5 and 24.9 is generally considered healthy, a BMI between 25 and 29.9 is considered overweight, and a BMI of 30 or higher is considered obese.
To explore the relationship between BMI and risk of ovarian cancer, researchers conducted a study among more than 94,000 U.S. women. During seven years of follow-up, 303 of these women were diagnosed with ovarian cancer.
- Overall, obese women were slightly more likely than healthy-weight women to develop ovarian cancer. This result did not meet the criteria for statistical significance, however, suggesting that it could have occurred by chance alone.
- By contrast, in the subset of women who had never used postmenopausal hormones, obesity was linked with an 83% increase in risk of ovarian cancer.
- Exploratory analyses also suggested that the link between obesity and ovarian cancer may vary by family history. Among women without a family history of ovarian cancer, there was a suggestion that obesity increased ovarian cancer risk. Among women with a family history, there appeared to be no association between obesity and ovarian cancer risk.
These results suggest that excess body weight may influence ovarian cancer risk by altering hormone levels. Among women who had never used postmenopausal hormones, obesity increased the risk of ovarian cancer. The researchers note, however, that additional studies will need to confirm these findings.
 American Cancer Society. Cancer Facts & Figures 2008. Available at: https://www.cancer.org/docroot/STT/stt_0.asp (Accessed January 7, 2009).
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