'Animal tests showed light, equivalent to that from street lamps, could lead to tumours becoming resistant to the widely used drug Tamoxifen,' the BBC reported in a summary of a study published in the journal Cancer Research.
Tamoxifen is a highly regarded drug that the World Health Organization lists as an essential medicine. It stops the female hormone oestrogen from fueling tumour growth.
But a patient's exposure to artificial nighttime light could impede it in a way related to light's damage to sleep, according to a team at the University of Tulane Medical School in New Orleans.
Earlier studies have shown that exposure to light – especially light in the blue wavelength spectrum such as that emitted by electronic gadgets, computers and TVs – impairs slumber because it suppresses the sleep-inducing hormone melatonin
The Tulane team added Tamoxifen to a study of lights and melatonin in rats. According to the BBC summary:
'Rats, with human breast cancer and treated with Tamoxifen, were left to sleep in a completely dark cage or one that had dim light. The scientists showed that in dim light, melatonin levels were lower, the tumours were bigger and were resistant to Tamoxifen. A second set of tests showed that giving those mice melatonin supplements kept Tamoxifen working and resulted in smaller tumours.'
Dr. Steven Hill, chair of the university's breast cancer research and one of paper's authors, said that he hopes to move the study into human breast tissue.
In the meantime, he advised patients to avoid light while sleeping.
'They could make sure they sleep in a room that is completely dark or they could wear eye-masks to let night-time melatonin rise and take Tamoxifen right before going to bed, that would be the easiest way to see if it works,' he said.
General avoidance of light at bedtime seems like a good idea for anyone regardless of their state of health, given the studies showing the havoc that night time light can wreak on rest.
It's all part of the wide open field of trying to understand the effect of light on human well being, which ranges from the damages caused to sleep on one hand, to using light to kill lethal bacteria and help humans to heal and learn on the other, with all sorts in between.
For more on light and human well being, visit the website of the nascent Lighting for People project.
Photo: Lightening down. The Tulane team, flanked by co-leaders Steven Hill on the left and David Blask on the right, with Robert Dauchy and Shulin Xiang, advise turning off the lights at night. Image is from Paula Burch-Celentano via Tulane University and Flickr.