Night light exposure in breast cancer patients, which shuts off production of melatonin, makes the condition resistant to drug tamoxifen, a new research shows.
Tamoxifen is a drug widely prescribed for breast cancer. Tulane University researchers and co-leaders of Tulane's Circadian Cancer Biology Group, Steven Hill and David Blask, along with team members Robert Dauchy and Shulin Xiang, examined the role of melatonin on the effectiveness of tamoxifen in warding off breast cancer cells implanted in rats.
The team found that melatonin, essential for success of tamoxifen, actually shuts down due to exposure to night time light.
"In the first phase of the study, we kept animals in a daily light/dark cycle of 12 hours of light followed by 12 hours of total darkness (melatonin is elevated during the dark phase) for several weeks," said Hill in a press release.
"In the second study, we exposed them to the same daily light/dark cycle; however, during the 12 hour dark phase, animals were exposed to extremely dim light at night (melatonin levels are suppressed), roughly equivalent to faint light coming under a door," Hill added.
Researchers explained that melatonin by itself slowed down formation of tumours and significantly reduced their growth. However, the researchers found that tamoxifen caused a dramatic weakening of tumours in animals with either high nighttime levels of melatonin during complete darkness or those receiving melatonin supplementation during dim light at night exposure.
The team said that the study results are helpful for women undergoing tamoxifen treatment. Moreover, the findings also are a warning for those exposed to light at night due to sleep problems, working night shifts or exposed to light from computer and TV screens.
"High melatonin levels at night put breast cancer cells to 'sleep' by turning off key growth mechanisms. These cells are vulnerable to tamoxifen. But when the lights are on and melatonin is suppressed, breast cancer cells 'wake up' and ignore tamoxifen," Blask said.
The study was published in the journal Cancer Research.
