Shift work, melatonin

In humans, poor sleep correlates with low plasma melatonin and can be improved by melatonin administration. This therapeutic approach has been tried especially in individuals whose sleep rhythms are disrupted by shift-work, blindness or jet-lag but its benefits are as yet unconfirmed and, in any case, the mechanisms by which it might reset sleep patterns are unclear. Of course, it must be remembered that other body... 

Melatonin has been promoted as a treatment for conditions ranging from jet lag to cancer (1,3-5) and is sometimes used for sleep induction (1) and shift work (6). Because melatonin is present in small amounts in some foods, it is licensed as a nutritional supplement in the USA. 

Melatonin is not currently recommended for enhancing sleep or adjusting to shift work because the factors (dose, timing, level of extant sleep debt) governing melatonin s effects have yet to be clearly elucidated—and, until then, a simplified doctrine applicable for military use is not possible. Although it has... 

Wrenn K, Wright S. Melatonin after night shift work. Ann Emerg Med 1999 33 479. 

Wright SW, Lawrence LM, Wrenn KD, Haynes ML, Welch LA, Schlack HM. Randomized clinical trial of melatonin after night-shift work efficacy and neruopsycholoigc effects. Ann Emerg Med 1998 32 334-340. 

Melatonin is an indole-derived anterior pituitary hormone that causes downstream inhibition of a-MSH-induced melanogenesis. Melatonin is antiamnesic, synchronizes circadian and circannual rhythms and is metabolized to 5-methoxytryptamine. Melatonin acts via GPCRs MT1 and MT2 (which both couple through Gai and cAMP decrease). MT1 may also couple via Gao and Gaq to activate PLC (and hence increase cytosolic Ca2+) and via G Gy activation of PLA2. Melatonin can further interact with nuclear receptor superfamily orphan retinoid receptors RZR/ROR. Melatonin fluctuates with a circadian rhythm and is elevated in blood during the night. Melatonin is accordingly of social importance in relation to shift work and jet-lag. Melatonin and 5-methoxytryptamine occur in some plants (Table 5.8). 

One of the most popular uses of melatonin has been in the treatment of rhythm disorders, such as those occurring with jet lag, shift work, or blindness. 

High levels of stress combined with lack of sleep or distorted wake/sleep cycles (e.g., shift work) leads to elevated levels of circulating cortisol. Cortisol depresses the synthesis and release of thymic hormones resulting in compromised development of T lymphocytes and a depressed immune response. Light inhibits the production of melatonin so its level falls when individuals have inadequate sleep. This reduces the melatonin-dependent inhibition of CRH release which amplifies the increase in circulating cortisol. The stress induced immunosuppression is therefore enhanced and prolonged. 

Foster Joe Takahashi, we echoed your work with the mouse. What is fascinating about the dynamic range of melatonin suppression is that it is so narrow compared with the three or four log unit range for phase shifting. 

Another reason to take melatonin during the day is if you are a shift worker and your schedule rotates every week or so. For example, Lisa worked as a receptionist at a hospital emergency room. As we all know, emergency rooms don t close for the night and must always have people on staff. Lisa s work schedule was to work 9 30 p.m. to 7 30 a.m. for seven nights and then have seven days off. Of course, during her seven days off... 

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