Several studies suggest there may be a connection between the hormone melatonin and cancer.
Melatonin is a hormone that helps regulate sleep. It also appears to influence other hormones in the body. Melatonin supplements have become popular as natural sleep aids.
Melatonin has been studied for cancer, however, and there is some speculation as to whether it may protect against cancer by preventing tumor cells from growing.
Researchers at Harvard evaulated 147 people with invasive breast cancer and 291 without cancer as part of the Nurses Health Study. They took a morning urine sample and measured melatonin levels via a melatonin by-product called 6-sulphatoxymelatonin. The researchers found women with the highest melatonin had the lowest risk of cancer.
At McMaster University in Canada, researchers did a systematic review of studies involving melatonin for people with solid tumor cancer and its effect on survival after one year. They analyzed 10 studies that were published between 1992 and 2003. The researchers found that melatonin reduced the risk of death at one year, regardless of the type of cancer. No serious adverse effects were reported. Researchers concluded that while it is a very promising treatment, well-designed studies were needed to further assess the safety and effectiveness of melatonin for cancer.
Spanish reaserchers evaluated melatonin supplements as a treatment for rats with advanced and untreated breast tumors. Melatonin given daily significantly increased survival in animals. The researchers concluded that the results strongly suggest that melatonin is beneficial during advanced breast cancer, because it increases survival time.
Although results have been promising, there isn't enough evidence to determine whether melatonin is safe or effective, and whether or not it might decrease the effectiveness of cancer therapies.
Mills E, Wu P, Seely D, Guyatt G. Melatonin in the treatment of cancer: a systematic review of randomized controlled trials and meta-analysis. J Pineal Res. 2005 Nov:39(4):360-6.
Saez MC, Barriga C, Garcia JJ, Rodriguez AB, Masot J, Duran E, Ortega E. Melatonin increases the survival time of animals with untreated mammary tumours: Neuroendocrine stabilization. Mol Cell Biochem. 2005:278(1-2):15-20.
Schernhammer ES, Hankinson SE.Cancer Inst. Urinary melatonin levels and breast cancer risk. 2005 Jul 20;97(14):1084-7.