melatonin

Normally, the production of melatonin by the pineal gland is inhibited by light and permitted by darkness. For this reason melatonin has been called 'the hormone of darkness'. The secretion of melatonin peaks in the middle of the night, and gradually falls during the second half of the night. Until recent history, humans in temperate climates were exposed to up to eighteen hours of darkness in the winter. In this modern world, artificial lighting typically reduces this to eight hours or less per day all year round. Even low light levels inhibit melatonin production to some extent, but over-illumination can create significant reduction in melatonin production. Reduced melatonin production has been proposed as a likely factor in the significantly higher cancer rates in night workers,[9] and the effect of modern lighting practice on endogenous melatonin has been proposed as a contributory factor to the larger overall incidence of some cancers in the developed world.[10] As inadequate as blood concentrations may be in brightly-lit environments, some scientists now believe that people's overnight output of melatonin can be further jeopardized each time they interrupt their sleep and turn on a bright light (suggesting that the lower brightness level of a nightlight would be safer).[11] Others suggest that such short exposures do no harm.

Major Side Effects

Melatonin can affect the normal body production or the supplemental use of certain hormones. Blood levels of human growth hormone (HGH) may be increased, while luteinizing hormone (LH) may be decreased. HGH stimulates growth in children and helps to regulate metabolism in adults. LH is important in the development of eggs and sperm. Other hormones may be affected, too. While no serious results have been identified, laboratory tests for these hormones may be inaccurate if the tests are performed during the same period that melatonin is taken. Individuals who take melatonin should inform their doctors before having any laboratory blood work.