Here’s a very interesting new study conducted at Tulane University that with very interesting findings study that led me to revisit the health benefits of melatonin.  The researchers found melatonin offers particularly strong protection against reproductive cancers. In particular, it determined that Tamoixfen, a breast cancer drug when given to animals who slept well and had normal melatonin levels killed the cancer cells while those who didn’t do.

Exposure to light at night, interrupts the normal cycle of melatonin production, and  renders breast cancer cells  completely resistant to tamoxifen, a widely used breast cancer drug. The study, “Circadian and Melatonin Disruption by Exposure to Light at Night Drives Intrinsic Resistance to Tamoxifen Therapy in Breast Cancer,” published in the journal Cancer Research, is the first to show that melatonin is vital to the success of Tamoxifen in treating breast cancer.

Principal investigators and co-leaders of the Tulane University Circadian Cancer Biology Group, Steven Hill and David Blask, along with team members Robert Dauchy and Shulin Xiang, investigated the role of melatonin on the effectiveness of Tamoxifen in combating human breast cancer cells implanted in rats.

“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,” says Hill. “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.”

Melatonin by itself delayed the formation of tumors and significantly slowed their growth but Tamoxifen caused a dramatic regression of tumors in animals with either high nighttime 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.

“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 says.

The study could make light at night a new and serious risk factor for developing resistance to Tamoxifen and other anticancer drugs and make the use of melatonin in combination with Tamoxifen, administered at the optimal time of day or night, standard treatment for breast cancer patients.

Melatonin Suppresses Alters Sex Hormones

Melatonin also has a calming effect on several reproductive hormones, which may explain why it seems to protect against sex hormone-driven cancers, including ovarian, endometrial, breast, prostate and testicular cancers. GreenMedInfo lists twenty studies demonstrating exactly how melatonin exerts its protective effects against breast cancer.

This powerful hormone also stimulates cancer cell death (aptosis), and enhances the production of immune stimulating chemicals like as interleukin-2, which helps identify and attack the mutated cells that lead to cancer. These two actions act together to enhance each other, synergistically! The most comprehensive aspect of melatonin research to date centers on breast cancer. For example:

  • The journal Epidemiologyreported increased breast cancer risk among women who work predominantly night shifts
  • According to an Israeli study, women residing in neighborhoods with large amounts of nighttime illumination are more likely to get breast cancer than those who live in areas where nocturnal darkness prevails, according to an Israeli study
  • From participants in the Nurses’ Health Study, it was found that nurses who work nights had 36 percent higher rates of breast cancer
  • Blind women, whose eyes cannot detect light and so have increased production of melatonin, have lower-than-average breast cancer rates
  • When the body of epidemiological studies are considered in their totality, women who work night shift are found to have breast cancer rates 60 percent above normal, even when other factors such as differences in diet are accounted for

Another study found that melatonin reduced the growth of prostate cancer. Studies show similarly encouraging results for lung, pancreatic, colorectal and other types of cancer. An article in Life Extension Magazine contains a table summarizing studies with one-year cancer survival rates that are vastly improved when melatonin is a treatment modality. Authors of a systematic review of melatonin for the treatment of all types of cancer concluded:“Effects were consistent across melatonin dose, and type of cancer. No severe adverse events were reported. The substantial reduction in risk of death, low adverse events reported and low costs related to this intervention suggest great potential for melatonin in treating cancer.”


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

Exposing Yourself to Light at Night Shuts Down Your Melatonin and Raises Your Cancer Risk


Life Extension Magazine