Melatonin is a hormone naturally found in humans. Its association with cancer has been shown in many studies assessing links between shift work and cancer rates, and shown a consistent relationship. The association between melatonin levels and cancer progression has suggested to some that melatonin may be a modifier of cancer progression. In this latest study, researchers examined all clinical trials assessing the role of melatonin as a therapy for solid tumor cancers. They used a methodology called meta-analysis, a technique of analyzing multiple studies. The authors reviewed 10 randomized clinical trials that included a total of 643 cancer patients with a variety of different solid tumor cancers. The types of cancers involved included lung, brain, skin, renal and breast cancer. "In this analysis, the effects appeared to be consistent across studies" say the authors. The researchers examined the effect of large doses of melatonin (10-40mg/day) on survival rates at one year. Melatonin reduced the risk of death at one year by 34%. "Effects this large certainly warrant further clinical trials" say the authors. The study also showed that melatonin was predominantly safe and had a beneficial effect on sleep patterns of patients.
All of the clinical trials involved in their study were from Europe from a related network of clinical researchers in Italy and Poland. The researchers, from McMaster University and the University of Toronto in Canada, say that their analysis also shows that clinical trials in North America should have been initiated back in 1996/7 as the results from Europe were consistent at that time. The Canadian researchers urge caution in interpreting the immediate clinical usefulness of large doses of melatonin and recommend patients discuss this with their physicians before beginning any treatments.
Dr. Dugald Seely, a cancer researcher at Sick Children's Hospital in Toronto and an author on the study, states, "This analysis shows a strong association. The small number of people needed to treat, low adverse events reported and low costs related to this intervention should be of substantial interest to patients, physicians and policy makers. Completion of independently conducted studies is required to confirm the efficacy and safety of melatonin in cancer treatment."
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.
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