Anti-estrogens probably work better if your sleep rhythm is better, and you produce more melatonin in the evening and at night. That is what cell biologists from Tulane University School of Medicine reported in Cancer Research in 2014. The researchers studied the impact of a healthy sleep rhythm on the effects of tamoxifen in an animal study. The results of their research are interesting for women with an estradiol-sensitive breast cancer variant, but also for pharmacological athletes.
The researchers implanted estradiol-sensitive MCF-7 breast cancer cells in mice. Some of those mice were in the dark at night [LD 12:12], another part was exposed to dim light at night [dLEN].
Some of the mice in the dLEN group received melatonin [dLEN-Mel].
When the researchers estimated the weight of the tumors at 1.5 grams, they gave the test animals tamoxifen, an anti-estrogenic drug that blocks the action of the estradiol receptor.
The administration of tamoxifen [TAM] had no effect on the growth of the tumors when the test animals were exposed to light [dLEN] at night, the figure below shows. But if the test animals that were exposed to light at night in addition to tamoxifen also received melatonin [MLT], their tumors suddenly reacted to tamoxifen.
Supplementation with melatonin brought the concentration of melatonin in the rats exposed to light at night at the levels of rats in the dark at night.
Melatonin, administrated as a supplement or released during a healthy sleep, inhibits the action of the estradiol receptor, the researchers discovered when they studied tumor cells from their test animals.
“In conclusion, the present investigation highlights and validates the importance of an intact endogenous nocturnal circadian melatonin signal in sensitizing human breast tumor cells to tamoxifen therapy”, the researchers write.
“Moreover, our work demonstrates that a comprehensive understanding and maintenance of host/cancer circadian biology and the circadian-regulated nature of cancer metabolism and signaling are essential to derive the maximal efficacy from tamoxifen and possibly other endocrine therapies.”
“It is plausible that many, if not all, patients with breast cancer are likely to be subjected to various degrees of light exposure at night and may be circadian/melatonin disrupted as a result of lack of sleep, and/or chronic late night shift work.
“Therefore, light exposure at night may represent a unique and previously unappreciated risk factor that could account for some forms of intrinsic and possibly acquired tamoxifen resistance and may even lead to a shortened survival time and even a decreased survival rate.”