Melatonin, a hormone secreted by the pineal gland, is stimulated by the onset of darkness, and is an important actor in the body's circadian cycle - the body clock.
Only one previous study (Laryngoscope, 1998, Vol. 108, pp. 305-310) has studied the effect of the hormone on tinnitus, a condition where the sufferer perceives a sensation of sounds without actual external source of sound. This reported no significant difference between the melatonin and placebo.
The study, published in the February issue of the journal Otolaryngology - Head and Neck Surgery (Vol. 134, pp. 210-213), reports the effect of a daily 3 mg for four weeks of a melatonin supplement on 18 participants with tinnitus.
The level of tinnitus was measured on the Tinnitus Handicap Inventory (THI) (scored between 0 and 100 - the higher the score the worse the tinnitus). At baseline, the average THI score was 35.4, which decreased to 28.8 after four weeks of melatonin supplementation.
The quality of sleep was measured using the Pittsburgh Sleep Quality Index (PSQI). At baseline, the mean PSQI score was 7.9, which decreased to 5.0 after supplementation.
"We found an improvement in tinnitus and sleep after taking melatonin. Furthermore, the degree of improvement in tinnitus was associated with the degree of improvement in sleep, however, due to a lack of control we can not establish causality," wrote lead author Uchechukwu Megwalu from the Washington University School of Medicine, St Louis.
Despite reporting a beneficial link between melatonin supplementation and tinnitus and sleep, the limitations undermine the strength of the link.
The study was not double-blind, placebo controlled, which meant that the patients knew they were taking melatonin, which might have affected the results.
The short-term, small population also questions any real benefits. Rightly, the scientists are planning a large prospective randomized placebo-controlled trial to further investigate any benefits.
Melatonin is currently available in the US as a 'dietary supplement'. According to the Nutrition Business Journal, US sales of melatonin were $67 million in 2004.