Melatonin is the natural sleep mechanism that is produced in the brains Pineal gland.

Levels gradually decrease with age.  A high carbohydrate diet lowers melatonin. Alcohol, caffeine and tobacco deplete melatonin. Bananas, cherries, tomatoes, and walnuts are high in melatonin

Melatonin has many other effects beside sleep onset. Is suppresses appetite during sleep. It relaxes muscles and nerves during sleep. It improves blood sugar metabolism and therefore reduces diabetes risk. Deficiency can contribute to obesity, cardio-vascular disease, osteoporosis and depression. Melatonin can induce the production of sex hormones. It protects the body from the toxic products (oxidants) that attack the body daily.  It has been shown to improve mitochondrial function.  It helps balance the stress hormone cortisol. It therefore improves mood. It improves the immune system. It also stimulates the production of all important growth hormone and thyroid hormone.

There is evidence that it is helpful in cancer protection (breast and prostate) and lifespan (more proven in animals)

There is also good evidence that melatonin is helpful in preventing Alzheimer disease and Parkinson’s disease

Symptoms of melatonin deficiency include nervousness, tenseness, and problems getting and staying asleep, mourning sleepiness, fatigue, depression, irritability and emotional behavior. Physical signs can include higher Blood pressure, lower heart rate, tense muscles, and appearing older.

Various preparations of Melatonin are available. For most people I recommend the 10 mg dose. For some with more severe problems initiating, sleep the 3 mg sub lingual is preferred. There are also sustained release products for those that re-awaken.