Sustained levels of high stress might affect estrogen levels -- which, over time, may have an influence on developing breast cancer, the study authors speculate. But this theory has not been tested, they caution.

A team of researchers from Denmark followed more than 6,500 women in Copenhagen for a period of eighteen years. At the beginning of the study, the women reported the levels of stress they routinely experienced as low, medium or high. Stress was defined as tension, nervousness, impatience, anxiety or sleeplessness.

Levels of Stress

The researchers adjusted for other factors that might have had an influence on the development of breast cancer. such as whether the women had children or whether they were menopausal. They did not account for such risk factors as family history of the disease, however.

Over the study period, 251 women were diagnosed with breast cancer for the first time. Women reporting high levels of stress were 40% less likely to develop breast cancer than women reporting low levels of stress, the researchers found.

Stress was calculated on a six-level scale; for every increased level of stress, women were 8% less likely to develop breast cancer.

Negative Consequences

Sustained levels of high stress might affect estrogen levels -- which, over time, may have an influence on developing breast cancer, the study authors speculate. But this theory has not been tested, they caution. Most research in this area has been restricted to animals.

In any case, stress-induced changes in hormonal balances are not a healthy response, they emphasize. Despite the favorable findings with respect to breast cancer, continued stress could cause other negative health consequences.