Sleeping at night with the lights on can not only add to your energy consumption, but also wake up breast cancer cells, a study suggests.
Exposure to light at night, which shuts off night-time production of the hormone melatonin, renders breast cancer completely resistant to tamoxifen, a widely-used breast cancer drug, the findings showed.
"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," said David Blask from the Tulane University in the US.
The researchers investigated the role of melatonin on the effectiveness of tamoxifen in combating human breast cancer cells implanted in rats.
Melatonin by itself delayed the formation of tumours and significantly slowed their growth but tamoxifen caused a dramatic regression of tumours in animals with either high night-time levels of melatonin during complete darkness or those receiving melatonin supplementation during dim light at night exposure.
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.
The study appeared in the journal Cancer Research.