Does Melatonin Put Cancer To "Sleep?"
BWH researchers continue to investigate nightshift-cancer link to see if lower melatonin levels play a role in tumor development
Boston, MA - Researchers at Brigham and Women’s Hospital (BWH), led by epidemiologist Eva Schernhammer, MD, DrPH, were among the first to report that nightshift workers may have an increased risk of developing breast cancer. Decreased levels of melatonin - a hormone closely linked to sleep patterns - is believed to be a possible cause. Now, in the next phase of this research, Schernhammer reports that lower melatonin levels are associated with a higher risk of breast cancer. The findings are published in the July 20, 2005 issue of the Journal of the National Cancer Institute (JNCI).
The hormone melatonin is typically released from the brain during the night. It is the reason people get sleepy. Nightshift workers, exposed to bright light during the evenings, produce less melatonin. Laboratory studies have shown that melatonin production can put tumor cells “to sleep” by stunting growth. A recent report indicated that in constant light, tumors grew seven times faster than they did in the dark.
In this study, the researchers measured urinary melatonin in 147 women who developed invasive breast cancer and 291 matched women who did not develop breast cancer. They found that women with the lowest levels of the melatonin metabolite in their urine were 70 percent more likely to develop breast cancer.
“This study brings us one step closer to understanding why nightshift workers may be more likely to develop cancer,” said Schernhammer, who is also an assistant professor of Medicine at Harvard Medical School. “The data from the urine samples we collected showed that women who went on to develop cancer had lower levels of a melatonin-metabolite, suggesting that women who produce less melatonin may be more susceptible to tumor growth, though this is still theoretical. As nightshift work becomes more common, it is important that in addition to confirming these findings, future research addresses how clock genes – genes that regulate a person’s 24-hour sleep-wake cycle - may impact melatonin production and tumor development.”
The next phase of cancer and melatonin research
BWH researchers recently received NIH funding to further study the effects of light at night on a person’s circadian rhythm, including their melatonin levels, by applying a novel device – a circadian lightmeter. Schernhammer, the principal investigator of the project, says that “this research will help clarify the role of light exposure in rotating shift workers based on recent information about the specific wavelengths that affect melatonin levels in humans. Specifically, we will measure light exposure by applying a new device, a circadian light meter, that captures the short wavelength portion of visible light, which has been described to most strongly suppress melatonin levels.” Schernhammer will relate those measures to the response of the circadian system of night workers, as measured by melatonin levels in their urine.
To understand more about melatonin’s influence on cancer outcomes, Schernhammer is involved in a second study that will test the hypothesis that blind women are less susceptible to breast cancer because they may have higher levels of circulating melatonin.
For more information on the study of “Reproductive and Hormonal Risk Factors for Breast Cancer in Blind Women” interested participants should call 1-888-828-4294. The study is open to all legally blind adult women in the US.
Please contact BWH Media Relations for more information at (617) 534-1600 or BWHMediaRelations@partners.org.
BWH is a 747-bed nonprofit teaching affiliate of Harvard Medical School and a founding member of Partners HealthCare System, an integrated health care delivery network. BWH is committed to excellence in patient care with expertise in virtually every specialty of medicine and surgery. The BWH medical preeminence dates back to 1832 and today that rich history in clinical care is coupled with its national leadership in quality improvement and patient safety initiatives, dedication to educating and training health care professionals, and strength in biomedical research. With $370M in funding and more than 500 research scientists, BWH is an acclaimed leader in clinical, basic and epidemiological investigation - including the landmark Nurses Health Study, Physicians Health Studies, and the Women's Health Initiative. For more information visit www.brighamandwomens.org
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