Melatonin and General Aging
Melatonin, a hormone primarily secreted by the pineal gland in the brain, is also produced in skin and hair cells. Melatonin is more than just the “sleep hormone” -- it regulates the circadian rhythm, which affects many metabolic and endocrine processes.
Melatonin, and the circadian rhythm more generally, plays a role in staving off aging. Melatonin levels decline as we age, and correspondingly circadian rhythms become less regular. Mice with mutations damaging their circadian rhythm have accelerated-aging syndromes, with obesity, diabetes, muscle loss, and shortened lifespans. Supplementing melatonin in rodents (or administering extracts from the pineal gland, or grafts from fetal pineal glands) has been found to extend lifespan, prolong fertility, reduce cancer incidence, reduce obesity and insulin resistance, and improve neurological recovery from brain injury. Melatonin and compounds that act along the same pathway have potential as aging-preventative drugs.
Melatonin administration also improves skin resistance to damage (such as from UV rays) and increases hair growth.
Melatonin and Skin
In both in-vitro skin culture experiments and human studies, administering melatonin prior to exposure to UV radiation increases cell survival and reduces oxidative damage. Topical melatonin applied to skin 15 minutes prior to exposure to UV radiation completely prevented skin redness (erythema) in a small randomized double-blind study of human subjects.
Melatonin and Hair: Animal and Human Studies
Melatonin also affects hair growth, as the hair growth cycle in mammals is under circadian control. As with other circadian cycles, the hair growth cycle becomes dysregulated and lower in amplitude with age. Mice whose circadian rhythms are damaged (via removal of the pineal gland or knockout of a circadian clock gene) show impaired hair growth as part of an accelerated aging syndrome. When pinealectomized rats are given injections of melatonin, their hair growth recovers to that of healthy rats. Melatonin administration has been found to increase hair growth in a variety of mammals: weasels, ewes , dogs, minks, goats, rabbits, raccoon dogs, and foxes , administered either orally or via subcutaneous implants. There’s a good evolutionary rationale for this effect: melatonin is the hormone that signals the onset of darkness, which triggers many mammals to grow thick winter coats as days grow shorter. In animals which grow white coats in winter and brown coats in summer, experimenters can trigger the growth of the white winter coat by administering melatonin.
There’s even evidence that topical melatonin can reverse hair loss in humans. In a randomized double-blind study of 40 women with hair loss, melatonin solution applied to the scalp increased hair growth significantly relative to placebo. In an open-label, uncontrolled study of topical melatonin involving 1891 male and female patients with androgenic alopecia, at 3 months 61% of patients had no hair loss, compared to 12.2% at the start; 22% had new hair growth at 3 months compared to 4% at baseline. The incidence of seborrheic dermatitis also declined, from 34.5% at baseline to 9.9% at 3 months.
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