New studies suggest people need to respect the body’s desire for nighttime darkness
By Janet Raloff
Web edition : Friday, January 23rd, 2009
NIGHT LIGHTS AND CANCER
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To stay healthy, the body needs its zzz’s. But independent of slumber, human health also appears to require plenty of darkness — especially at night. Or so suggests a pair of new cancer studies.
One found that among postmenopausal women, the lower the overnight production of melatonin — a brain hormone secreted at night, especially during darkness — the higher the incidence of breast cancer. The second study correlated elevated prostate cancer incidence around the world with places that have the brightest signatures of light in satellite imagery.
Trends seen in both studies bolster animal data indicating that natural nighttime peaks in blood concentrations of melatonin, which tend to occur during sleep, depress the growth of the hormonally sensitive cancers.
Light will depress the body’s natural secretion of that hormone, whether someone is awake or asleep.
In 2001, Eva S. Schernhammer of Brigham and Women’s Hospital in Boston and her colleagues found an elevated risk of breast cancer among women who worked night shifts. The data, gleaned from participants in the long-running Nurses’ Health Study, fit with the idea that the light encountered while working nocturnal hours would have suppressed the women’s melatonin production.
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