Scientists suggest that total darkness at night time is important for breast cancer treatment.

They said that breast cancer becomes resistant to tamoxifen, widely used hormonal therapy, if exposed to light at night.

According to the researchers at the Tulane University, New Orleans, U.S., such exposure is capable of shutting off night time production of the hormone melatonin.

This hormone is necessary for the success of the drug used in treating breast cancer, says the study which was published in Cancer Research Journal.

The role of melatonin on effectiveness of tamoxifen in combating human breast cancer cells that were implanted in rats was examined by the researchers who found that melatonin delayed formation of tumours and also slowed its growth significantly.

Co-leader of Tulane's Circadian Cancer Biology Group, Steven Hill said the study does not identify how much light exposure is required to inhibit night time melatonin production, and possibly drive tamoxifen resistance in humans, but we belive that it can be as little as the amount of light that comes in the window from a street light.