© 2005 American Thoracic Society
Melatonin for Patients with AsthmaSafety and Efficacy Are Still DubiousTo the Editor:We read with interest the article by Campos and colleagues (1). The main problem with commercially available melatonin is that it is sold as a health food, rather than as a medication. As a result, the different brands of melatonin have widely different pharmacokinetics. Because of the variability of melatonin preparations, the findings of Campos and coworkers may not be applicable to brands of melatonin other than that used in their study. It is unfortunate that the brand name of the studied melatonin was not mentioned by the authors. Another problem of the study is the statement that chronic use of melatonin at 3 mg per day was safe based on a single paper. Other papers suggested possible side effects of melatonin including infertility, hypothermia, retinal damage, elevated blood pressure, diabetes, cancer, and depression (2). One should appreciate that a 0.5 mg dose was reported to be the cutoff between "high physiological" and "low pharmacological" (3). Therefore, 3 mg per day as used in Campos and coworkers' study is a pharmacological dose. It would be difficult to justify using a pharmacological dose of hormone for a long period when the endogenous secretion of melatonin might be normal. The selection of females only as studied subjects is not acceptable despite the explanation by the authors that males metabolize melatonin three times faster than females (4). Another study found no sex differences in the pharmacokinetics of melatonin in adults (5). If the authors were certain on this aspect, they could enroll male subjects to receive 9 mg of melatonin per day. Moreover, the method of randomization in Campos and coworkers' study was not clearly stated and the Jadad score for assessing quality of a randomized controlled trial was low at 3, as more than 3 should be regarded as acceptable (6). The use of an actigraph is well recognized as a marker of sleep duration. It is surprising that Campos and coworkers did not use this noninvasive device, which can objectively document sleep duration. In conclusion, Campos and coworkers' study must be viewed with great caution and melatonin should only be given on a research basis.
Kwong Wah Hospital, Hong Kong, China FOOTNOTES Conflict of Interest Statement: D.K.N. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript; C.-H.C. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript; P.-Y.C. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript; K.-L.K. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
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