Lack of Sleep Linked to Higher Breast Cancer Risk,

Lack of Sleep Linked to Higher Breast Cancer Risk

November 04, 2008 01:58 PM
by Anne Szustek
Research from a Japanese university suggests that a lack of melatonin may disrupt release of estrogen, thus increasing the risk of breast cancer.

Possible Link Between Sleep Disruption and Breast Cancer

A team of scientists at Japan’s Tohoku University Graduate School of Medicine analyzed the lifestyle habits over eight years of nearly 24,000 women ages 40 to 79. The women who slept six hours or less a night on a regular basis were 62 percent more likely to develop breast cancer than those who slept seven hours.

The research team postulates that melatonin may suppress the release of estrogen, which is considered to be a possible factor in development of breast cancer cells.

Melatonin is a hormone whose release is stimulated by waning levels of light. Concentrations of melatonin are highest in the hours just prior to bedtime. Sitting in artificial light—such as when staying up late—can inhibit melatonin production, however.

Reactions to the study by other medical researchers have been mixed. Dr. Steven Narod of Toronto’s Women’s College Hospital told Canadian news site CityNews, “There are at least two other studies where women who slept shorter periods were found to have an increased risk of breast cancer.”

Henry Scowcroft, the science information manager for Cancer Research UK, acknowledged the possibility of a link between lack of sleep and breast cancer. However, he told The Daily Telegraph, “it’s too early to tell whether this effect is important when compared with other known lifestyle risk factors like weight, exercise and alcohol consumption.”

In the same Telegraph article, sleep medicine professor Jim Horne, who teaches at Britain’s Loughborough University, blasted the Japanese study. “The number of cancer cases in this study is very small and I suspect the risk only starts increasing under five hours a night,” he said. “[T]here is no good evidence that sleeping for longer helps to prevent breast cancer.” During the course of the eight-year Tohoku University study, 143 of the subjects were diagnosed with breast cancer.

Background: Recent breast cancer studies

In August, the Fred Hutchinson Cancer Research Center in Seattle released a study that suggested breast-feeding may reduce the risk of two aggressive types of breast cancer: luminal cancer and a type of cancer known as triple negative cancer, which is common among African Americans and Hispanics, especially in younger women. Researchers have proposed two theories to explain why:  a woman who is breast-feeding has stopped menstruating and her “hormones aren’t cycling”; a second possibility is that the cell structures in a woman’s breast change in such a way that they might be less capable of forming cancerous cells.

In light of such research showing the health benefits for mothers who nurse their infants, some hospitals are ending the long-standing practice of offering baby formula samples to new parents.

“Formula sample packs have been shown to undermine breastfeeding, and their elimination from U.S. hospitals may help to increase exclusive breastfeeding rates nationally. The prevalence of sample pack distribution is disturbing and incongruous given extensive opposition, but encouraging trends suggest that the practice may be curtailed in the future,” researchers were quoted as saying by WebMD.

Other recent research casts doubt on a practice long considered a straightforward way to reduce breast cancer risk: breast self-exams. The Cochrane Collaboration released a study in July that showed that among the 587 study participants who died of breast cancer during the course of the research, 292 of them had regularly performed breast self-exams and 295 had not, “a minuscule difference that suggests there is no benefit from self-checks,” Time magazine reported.

Reference: Breast cancer


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