New research indicates light and dark conditions may contribute to breast cancer risk.

"Women who worked night shifts or who were exposed to light in the nighttime hours when most people are asleep had an increased risk of breast cancer," said Dr. Catherine Welsh, an oncologist

The researchers said the constant exposure to light prevents women's bodies from needed darkness. They said a small gland deep in the brain produces melatonin, but exposing eyes to light turns off production of melatonin, which is a hormone that appears to offer protection against cancer cells.

Sleeping with the television or light on, and working at computers late at night, can also turn off melatonin.

So, how important is this chemical? In another study, researchers implanted breast cancer cells in rats and gave them blood from subjects exposed to either darkness or light at night.

Welsh said that study found that the bright light exposure caused the breast cancer cells in the blood to grow at a faster rate than the tumors exposed to blood from people who remained in the dark.

At this point, cancer experts do not recommend taking over-the-counter melatonin supplements.

"We really don't know how it works and whether, in fact, it reduces the risk of breast cancer," said Dr. Atif Hussein, a hematologist.

To increase melatonin naturally, health experts recommend ensuring your room is as dark as possible and, when it's time for sleep, turn off the TV and any lights to give your body the darkness it needs.

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