Light Exposure at Night



The results of several studies suggest that women who work at night — factory workers, doctors, nurses, and police officers, for example — have a higher risk of breast cancer compared to women who work during the day. Other research suggests that women who live in areas with high levels of external light at night (street lights, for example) have a higher risk of breast cancer.

Researchers think that this increase in risk is linked to melatonin levels. Melatonin is a hormone that plays a role in regulating the body’s sleep cycle. Melatonin production peaks at night and is lower during the day when your eyes register light exposure. When women work at night or if they’re exposed to external light at night, their melatonin levels tend to stay low.

Steps you can take

It’s not clear how much darkness is required to turn on melatonin production. Closing your eyes does a fairly good job of blocking light, but thick curtains or an eye mask can make sure you’re sleeping in darkness. If you’re concerned about excess light exposure at night, you may want to:

  • install blackout shades on your bedroom windows
  • don’t turn on lights if you wake up at night
  • use low-wattage or red bulbs in nightlights
  • install a low-wattage or red-bulb nightlight in your bathroom(s)

Many people say taking melatonin supplements helps them sleep better. Still, no research has looked at taking melatonin supplements and breast cancer risk. Before you take any supplements, talk to your doctor about the risks and benefits of the product.

TPLG Booklet ThumbnailThink Pink, Live Green: A Step-by-Step Guide to Reducing Your Risk of Breast Cancer teaches you the biology of breast development and how modern life affects breast cancer risk. Download the PDF of the booklet to learn 31 risk-reducing steps you can take today.


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