Women who work night shifts may have a 60 percent greater risk of breast cancer. This finding may be due to the body?s response to light, according to researchers at the Fred Hutchison Cancer Research Center in Seattle.

A gland in the brain known as the pineal gland produces the hormone melatonin when the body is exposed to sunlight or artificial light. This production is disrupted when people are up at night with the lights on.

?Exposure to light at night may increase the risk of breast cancer by suppressing the normal nocturnal production of melatonin by the pineal gland which, in turn, could increase the release of estrogen by the ovaries,? the researchers say. Breast cancer is linked with production of the female hormone estrogen.

Scott Davis and his team studied 813 patients aged 20 to 74 who had breast cancer, and compared them to 793 women who did not have the disease. They asked the women about their work and sleep habits and bedroom lighting in the previous 10 years. ?Graveyard shift work was associated with increased breast cancer risk,? the researchers wrote.

They found that the increased risk was 60 percent, and the more hours the women worked overnight, the higher their risk was. They say the women they studied had twice the risk of breast cancer if they worked at least four and a half years of night shift work and were awake from 1 a.m. and 2 a.m. at least three nights a week.

Davis says his team got the idea to check the links between light exposure and breast cancer after studies were done showing that blind women have a lower risk of breast cancer. They also say there is a very slightly higher risk of breast cancer in women whose bedrooms are the brightest at night. But getting up once in a while does seem to increase risk. ?Risk did not increase with interrupted sleep accompanied by turning on a light,? according to their research.

They say more study is needed before doctors start recommending that women avoid night shifts. For one thing, it may not actually be light that is causing the effect. ?Among shift workers, quite a number of factors could affect the mechanisms that control the body?s circadian rhythms,? Davis says. ?One is stress, considering the kinds of shift work, from police, fire and rescue work to nuclear power plant monitoring to factory work, medicine and nursing.?

?There is an urgent need for further exploration of the relationship between exposure to light at night, shift work, including timing during the night, and cancers that may be influenced by melatonin,? agrees Johnni Hansen of the Danish Cancer Society in Copenhagen.

Ladies: Shut your blinds tight when you go to bed, turn off the night light and avoid the night shift.

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