July 9, 2004 -- Stress may increase women's risk of breast and endometrial cancer more than drinking alcohol, according to a new study in animals.
Researchers found stressed-out female monkeys who were subservient to other monkeys had a higher risk of endometrial cancer than the more dominant monkeys. Endometrial cancer is cancer of the lining of the uterus, called the endometrium.
"We know that lower social status is stressful for both humans and monkeys," says researcher Carol Shively, PhD, professor of comparative medicine at Wake Forest University Baptist Medical Center, in a news release. "This study shows that in monkeys, social stress was associated with cellular changes that may increase endometrial cancer risk."
Endometrial cancer is usually diagnosed in women over 50. The risk of this type of cancer is increased by the presence of estrogen, either occurring naturally or from hormone therapy in postmenopausal women.
Previous studies have linked estrogen to breast cancer, while other human studies have shown that alcohol appears to increase the risk of breast cancer. Alcohol may cause an increase in the level of estrogen. But researchers say many of these studies relied on women reporting how much they drank, and studies show most people don't accurately report their alcohol consumption.
However, an association between alcohol and endometrial cancer has not been seen in human studies.
Stress Raises Cancer Risk
In the study, which appears in the current issue of the journal Menopause, researchers looked at the effects of social stress and alcohol on the risk of breast and uterine cancer in female monkeys who had their ovaries removed.
The monkeys were placed in groups so they would form a natural social hierarchy from dominant to subordinate. In addition, the monkeys were taught to drink the human equivalent of two alcoholic drinks per day or a placebo for 26 months.
At the end of the study, researchers found that compared with dominant monkeys, the subordinate monkeys were at increased risk for endometrial cancer, as shown by an increase in growth of cells in the uterus -- similar to the effect seen when estrogen is given without the hormone progestin.
The subordinate monkeys also had thicker breast tissue, but these changes were not as significant as the changes in the uterus.
"The results from this study tell us that we need to look much more closely at the effects of stress and socioeconomic status on risk for endometrial and breast cancer in women," says Shively.
Alcohol and Women's Cancer Risk
Researchers also found no difference in breast or uterine cancer risk between the monkeys who drank a moderate amount of alcohol and those who didn't drink. This suggests that social status was more important than alcohol consumption on the risks of breast and endometrial cancer.
"The research suggests that moderate alcohol consumption in postmenopausal women not taking hormone therapy may not be harmful to health," says Shively. But she says these results may not apply to women who use hormone therapy or premenopausal women.