THURSDAY, Sept. 8, 2005 (HealthDay News) -- Here's news that could ease worries about breast cancer: Women with higher levels of daily stress showed a lower risk of developing the disease, according to new research.
But that's no reason to increase your stress levels, said the study authors.
"Even though we find a lower risk of breast cancer among stressed women, let me just emphasize that stress cannot be considered a healthy response," said study lead author Naja Rod Nielsen, a research assistant at the National Institute of Public Health in Copenhagen, Denmark.
"Stress is not a desirable state and it may lead to the development of other disease, particularly cardiovascular disease," Nielsen said.
So what does this information potentially contribute?
"Stress is a large problem, especially in the westernized world, and this study may help us understand some of the mechanisms behind breast cancer and how stress actually affects breast-cancer risk," Nielsen said. "Further, some women may partly blame their own stressful lifestyle when diagnosed with breast cancer. Hopefully, this and other studies may counteract such reactions."
The study findings appear in the Sept. 10 issue of the British Medical Journal.
Other experts, however, urged caution when interpreting the results.
"It's certainly not firm. The findings are based on small numbers. It's borderline statistically significant and they haven't given any good biological correlate to what the measure shows," said Heather Spencer Feigelson, a senior epidemiologist with the American Cancer Society. But "it suggests that stress doesn't cause breast cancer and that's probably true."
While some researchers have studied the effect of acute stress -- such as the death of a family member -- on breast cancer, less attention has been paid to the impact of routine daily stress.
The researchers examined data on 6,689 women participating in the Copenhagen City heart study. At the beginning of the study (1981-83), participants were asked about their levels of routine, daily stress -- defined as anxiety, impatience, nervousness, sleeplessness or tension. The women were followed until 1999.
During the 18 years of follow-up, 251 of the participants were diagnosed with breast cancer. Women reporting high levels of stress were 40 percent less likely to develop breast cancer than women reporting low levels, the researchers report.
For each increase in stress level on a six-point scale, women were 8 percent less likely to develop breast cancer. The association was more pronounced in women receiving hormone therapy, the study found.
What might explain the findings? The researchers speculate that stress activates stress hormones which may, in turn, limit the body's production of estrogen, a well-known risk factor for breast cancer.
Hormone-sensitive women (such as those taking hormone therapy) are more likely to be susceptible to stress-induced changes in estrogen, which could explain why the association was more dramatic in this group, the authors said.
This explanation does seem to back up another recent study that found that seaweed may help protect against breast cancer. Kelp seaweed may reduce the amounts of estrogen circulating in the body, the study suggested.
Still, all of this is just hypothetical, the authors of the new study cautioned.
"The mechanisms behind the observed lower risk of breast cancer among stressed women remain unknown," Nielsen said. "One hypothesis is that prolonged activation of stress hormones can lead to lower production of estrogens, which is a main risk factor for breast cancer. This hypothesis is only based on experimental data and remains to be confirmed in humans.
"It would be an obvious next step in this line of research to address the validity of this hypothesis in humans, and it is something we are currently working at. It would also be very interesting to see if these findings can be replicated in other studies," Nielsen said.
More information
To learn more about preventing breast cancer, visit the National Cancer Institute.
