Women who feel stressed out may be less likely to develop breast cancer than their mellower peers, Danish researchers report intheBritish Medical Journal.

But the scientists aren’t trumpeting the benefits of stress. They warn that feeling stressed can take a big toll on the body.

If that sounds like a mixed message, don’t fret. Here is the scientists’ theory: High stress levels crank up production of stress hormones. Over time, that throws off estrogen production -- a growth factor for some breast cancers. Less estrogen means less breast cancer, write Naja Rod Nielsen and colleagues.

Nielsen is a student and research assistant at Denmark’s National Institute of Public Health.

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Stress Study

Nielsen’s team looked at data from more than 6,600 women in Denmark. The women had enrolled in a long-term study of heart health.

When the heart study started, the women were about 50 years old. They rated the intensity and frequency of their tension, nervousness, impatience, and sleeplessness.

What upsets one person may not bother another. That’s why the researchers asked the women about feelings, not sources of stress.

The women were followed for up to 18 years. During that time, 251 women had their first breast cancer diagnosis.

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High Stress, Breast Cancer

Women who reported high stress levels at the study’s start were 40 percent less likely to be diagnosed with breast cancer during the study than those who had reported low stress levels.

That was especially true of women who were receiving hormone therapy. For those women, every increase on a six-point stress scale brought an 8 percent drop in breast cancer risk, write the researchers.

The jury is still out on how stress affects breast cancer risk. The Danish findings contradict several other studies, note Nielsen and colleagues. They add that one of those studies focused on extremely stressful life events, not day-to-day stresses.

“A greater risk of breast cancer associated with stressful life events is not necessarily in contrast with a lower risk of breast cancer associated with daily stress,” write Nielsen’s team.

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The Down Side

The news wasn’t all good for the highly stressed women. A bigger percentage of them died during the study, compared with the more mellow women.

About 39 percent of the most highly stressed women died before the study ended. So did 35 percent of those who had reported low stress levels and 30 percent of those who had noted moderate amounts of stress.

“Stress-induced disturbances ... cannot be considered a healthy response, and prolonged stress may have harmful effects on a range of other diseases, especially [heart] diseases,” write the researchers.

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The Fine Print

The women only took the stress survey once. It’s not known if their stress levels changed later.

Several breast cancer risk factors were considered, including menopause, body mass index, use of hormone replacement therapy or oral contraceptives, number of children, physical activity, alcohol use, and education.

But some other important risk factors -- family history of breast cancer, age at first menstrual period, age at first full-term pregnancy -- weren’t noted, write the researchers.

Visit WebMD's Breast Cancer Health Center

Dealing With Stress

It may be possible to cut some stressors out of your life. But you probably can’t get rid of all your stress.

So it’s a good idea to learn to handle stress.

Exercise, counseling, meditation, and stress reduction classes are just a few ideas to consider. The goal: Find a way to unwind before stress unravels you.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Nielsen, N. British Medical Journal, Sept. 10, 2005; vol 331: pp 548-550. News release, British Medical Journal.