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  July 30, 2001

Nighttime light Exposure May Increase Cancer Risk

Exposure to high levels of night-time light may be related to an increased risk of breast cancer, according to a researcher at the Health Center.

Richard Stevens, a cancer epidemiologist in the Department of Community Medicine and Healthcare, believes ill-timed light disrupts basic body rhythms - circadian rhythms - and may affect the production of certain hormones, such as melatonin.

His theory is based on animal studies and biology.

The idea is: At night, when it's dark, the hormone melatonin is secreted. Light can interfere with hormone production cycles and reduce the amount of melatonin made. Melatonin may influence production of estrogen in such a way that reduced amounts of it may lead to elevated estrogen. And elevated estrogen is known to increase the risk of breast cancer.

Additional work carried out in the U.S. and Sweden offers some support for Stevens' hypothesis: blind women - unable to perceive light at night - have lower rates of breast cancer.

What to do? "Get a dark night's sleep," Stevens suggests.

That may be easier said than done. Electricity has changed the way we live. In fact, Stevens says, we have reached a point in our evolution where we are almost precisely opposite where we need to be: our nights are now filled with light and our days are void of the natural brightness provided by the sun.

In other words, we live in lighted nights and dark days, but what our bodies need is dark nights and bright days.

In the evening, light from lamps, headlights, street lights, television, spotlights, floodlights and a thousand other sources surrounds us.

During the day, we go indoors to work, where the light is provided by electricity and usually by fluorescent lamps.

Whereas our forebears were outdoors working with the sun shining brightly on them, many of us are indoors, often in cubicles and under fluorescent lighting, which is incomparably weaker than natural light.

The reversed pattern of lighted nights and dark days may also contribute to the growing number of those with Seasonal Affective Disorder, a condition whose symptoms find sufferers typically feeling low, slow, depressed, and withdrawn, Stevens says.

The solution to the disorder is exposure to strong light in the morning.

To improve people's chances of obtaining a dark night's sleep, Stevens suggests:

  • not watching television or reading too late in bed; and
  • acquiring a red nightlight to guide people to the bathroom. The red light should be sufficient to illuminate the way, but not so bright as to interfere with melatonin production.

"You need enough light to make your way safely," he says, "but not as bright as a bank of ordinary bathroom lights."

Pat Keefe

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