Artificial Lighting During Sleep Linked to Breast Cancer

We’ve all heard studies on how even the slightest bit of light during sleep can affect our mood and sleep patterns. But new compelling research shows it may also have a link to melatonin levels affecting breast cancer.

In the study, conducted with lab rats with human breast tumors, shows that exposing the rats to a dim light during the night, made the tumors resistant to tamoxifen, a breast cancer drug.

The study, published in the journal Cancer Research, features the first study showing a direct correlation between melatonin levels and the effectiveness of tamoxifen.

Lead researcher Steven M. Hill, from Tulane University said, "Resistance to tamoxifen is a growing problem among patients with hormone receptor-positive breast cancer. Our data, although they were generated in rats, have potential implications for the large number of patients with breast cancer who are being treated with tamoxifen, because they suggest that nighttime exposure to light, even dim light, could cause their tumors to become resistant to the drug by suppressing melatonin production."

The first part of the study involved keeping the rats in an environment of 12 hours of light followed by 12 hours of total darkness (darkness elevates melatonin levels) for several weeks. In the second phase, the researchers exposed them to the same daily light/dark cycle, however, during the 12 hour dark phase, a dim light (equivalent to a faint light coming under a door) was left on—essentially suppressing melatonin levels.

The rats that remained in the darkness through the night had elevated melatonin levels (as we all do) and then levels dropped as the light began to flood the room in the morning.

In rats sleeping with the dim night light, melatonin levels remained low throughout the the night and day.

Tumor growth in the rats exposed to light at night had increased the breast tumor 2.6 times faster compared with tumor growth in rats living in normal light/dark conditions.

Additionally, the rats who were exposed to the dim night light were completely resistant to tamoxifen, as opposed to the tumors in rats living in normal light/dark conditions, whose tumors regressed significantly. Moreover, if the rats living in dim night light conditions were given a nighttime melatonin supplement, their tumors regressed.

"These findings have potentially enormous implications for women being treated with tamoxifen and also regularly exposed to light at night due to sleep problems, working night shifts or exposed to light from computer and TV screens," says Hill.

Hill, however, is not yet comfortable recommending Melatonin supplements for cancer patients with breast cancer. Of course, nature is always best and darkening your bedroom may be key.

Hill explains,"These data suggest that, in the not-too distant-future, it may be possible to combine melatonin and tamoxifen. However, before this is done we would need to identify the optimal times of day to give the two because if the timing between the two is off, the advantage of giving them in combination may be lost. This brings up another important point: Our levels of melatonin are not determined by sleep, as many people think. It is actually the darkness that is important. During the night, if you sleep in a brightly lit room, your melatonin levels may be inhibited; however, if you are in the dark but cannot sleep, your melatonin levels will rise normally."

Moral of the story—get your bedroom completely dark during sleep. Also, get more natural light. Instead of cutting on the lights during the day, try instead to open all the blinds and let the natural light in. Direct sun exposure is also linked to better sleep and at night (at least at a certain time) cut off all the lights to get your body ready for sleep and used to the natural circadian rhythms.