Posted July 31, 2014 by Bernard J. Baars in aging

Turn the lights off when you sleep: Melatonin and cancer treatment.

Dog in sleepA spectacular study by Dauchy (et al, 2014) shows that sleeping in total darkness makes a big difference in anti-cancer treatment. The drug tamoxifen is widely used to treat breast cancer. But tamoxifen interacts with the body’s natural hormone cycles, notably the release of melatonin in the pineal gland of the brain. Melatonin-release is triggered by darkness, and helps us to get to sleep.

Now it seems that tamoxifen stops fighting cancer if experimental mammals have a disrupted sleep cycle that inhibits the normal secretion of melatonin when darkness falls. Rats were used in this case, for ethical reasons. In terms of basic bodily functions, rats have many similarities to humans, and in this case the researchers focused on an estrogen receptor that we have in common with rodents, called ER alpha+. (ER = estrogen receptor, and alpha + is just a convenient code for different estrogen receptors).

Dauchy (et al) write that

“Resistance to endocrine therapy is a major impediment to successful treatment of breast cancer. … Disruption of circadian rhythms by night shift work or disturbed sleep-wake cycles may lead to an increased risk of breast cancer and other diseases. Moreover, light exposure at night … suppresses the nocturnal production of melatonin that inhibits breast cancer growth.”

While this is basic research, it has some obvious implications for preventive medicine.

First, a good night’s sleep is invaluable.

Second, turning the lights off completely — as happens in nature — helps the anti-cancer hormone melatonin to be expressed at night, when the body is ready for it.

Third, as we get older and lose some of our natural melatonin, it might make sense to take a little bit of melatonin before going to sleep (in a DARK room).

Fourth, even a small amount of light at night seems to inhibit melatonin release.

Finally, people at risk for breast cancer should take special care to get plenty of natural sleep — meaning regular sleep-waking cycles linked to the day-night rhythm.

And… independent research shows that a moderate amount of sunlight exposure during the day also promotes health, including emotional health.

It seems that frontier science supports folk wisdom through the ages.


Robert T. Dauchy et al. Circadian and Melatonin Disruption by Exposure to Light at Night Drives Intrinsic Resistance to Tamoxifen Therapy in Breast CancerCancer Research, July 2014 DOI: 10.1158/0008-5472.CAN-13-3156

Reusable under Creative Commons license.

 Editorial opinions do not represent MBSci as a nonprofit corporation. 

The Society for Mind-Brain Sciences is a 501 c(3) nonprofit corporation. To join the Society, please visit our website, The membership page is here. 

To receive FREE WEEKLY UPDATES of A Conscious Brain blog, please provide your email address on our frontpage.

Your privacy will be protected, and you can unsubscribe at any time.



Bernard J. Baars