It’s long been understood that darkness is most conducive to a good night’s sleep and helps spur the production of sleep-causing chemicals, but doctors recently revealed just how disruptive sleeping with lights on can be to a person’s health.

The American Medical Association recently adopted a policy recognizing that exposure to light during nighttime can ruin sleep, especially in teens and children. In fact, it might even increase one’s risk of cancer.

Animals exposed to light for 24-hours a day experience a dramatic increase in the risk of certain types of cancer. Studies show that people who wake frequently at night, or who are exposed to bright light at nighttime, have a higher risk of breast cancer. Bright lights during sleep interfere with the production of the neurotransmitter melatonin, which is thought to potentially be a cancer suppressor.

Dr. Mario Motta, a member of the AMA Council on Science and Public Health, says it shouldn’t be surprising that nighttime lights have a negative effect on people, especially given the fact that humans evolved over millions of years with a consistent 12-hour cycle of light and dark.

As to a way to reduce risk, Motta suggests that children are kept on regular sleep schedules and put to bed in dark rooms. If a child is afraid of the dark, however, a dim red light can be used. But above all, he said, turn off all electronics at night, since they emit blue light, which is known to suppress melatonin.

[MSNBC]