Night-shift workers who had low levels of the body’s vital “sleep hormone” were significantly more likely to develop breast cancer than those who were awake during the day but got plenty of shut-eye at night, a team of scientists is reporting.
The analysis by Boston researchers goes straight to the heart of a question scientists have asked for years: Are night-shift workers, because of extended exposure to light, more likely to develop cancer?
“Two or three years ago we probably would have been reluctant to say there was an association,” said Dr. Eva Schernhammer, an epidemiologist at Brigham and Women’s Hospital. “But now the evidence is becoming clearer” that a relationship exists, she said.
During daylight or exposure to bright lights, the hormone melatonin is suppressed. Switch off the lights, and melatonin, secreted by the brain’s pineal gland, begins to stream into the blood. The hormone flows most copiously during sleep, thus its nickname, the sleep hormone.
A growing number of scientists theorize that melatonin also suppresses the growth of cancer cells.
Laboratory studies by researchers at the University of Arizona have shown that breast cancer cells stop proliferating in melatonin’s presence. And Dr. David Blask of the Bassett Research Institute in Cooperstown, N.Y., found that melatonin serves as an anticancer signal to human breast cancers.
Schernhammer, who reported her results in today’s Journal of the National Cancer Institute, said women exposed to light at night had measurably lower levels of a melatonin breakdown product in urine.
“This is an interesting bit of new information, and it will be put in context with other studies,” said Dr. Brian O’Hea, director of the Carol Baldwin Breast Care Center at Stony Brook University Hospital.
