Why we sleep at night is linked to pineal gland, a pea-sized gland located in the brain. It secretes a neurohormone melatonin. At day the pineal gland is inactive, but at night it secretes high levels of melatonin, which makes sleep all the more inviting to all of us.

Because of its involvement in the body's circadian rhythm, consumers are driven to think of it as a sleep inducer, especially when attacked by insomnia or jet lag.

Just how effective it is in curing insomnia has been a subject of many scientific studies, and results so far are mixed. Some have shown positive findings, but most had significant limitations, like the duration of the studies or lack of female participants.

If you have insomnia, it is recommended to know its underlying cause. Modifications to present lifestyle and sleeping environment also help, as some factors when changed or eliminated have shown to bring improved quality of sleep to some people for a long time.

Another notion worth of attention here is the levels of melatonin in old people compared to those in younger people. Many elders have trouble falling asleep, and it is attributed to their declining melatonin levels. However, a recent study had cast doubt on the popular notion that melatonin levels actually go down as people age.

A team consisting of Dr. Charles Czeisler, M.D., Ph.D. and his colleagues at Harvard Medical School and Brigham and Women's Hospital studied 34 healthy elders, male and female, free from sleep disorders and medications ranging from 65-81 years of age, by comparing their nighttime melatonin levels with those from 98 younger men aged 18-30.

By taking and analyzing their blood samples, they discovered that the melatonin levels of the older group had no significant difference from those belonging to the younger group.

"The idea that a pineal aging clock winds down as you get older is simply not true," says Jamie Zeitzer, Ph.D. "Being older does not cause a person to have low melatonin levels. While we know that some older individuals have low melatonin levels, it isn't because of their age per se."

However, melatonin as a supplement seems promising in fighting jet lag and in promoting daytime sleepiness.

Dr. James K. Wyatt of Rush University Medical Center and his colleagues at Harvard Medical School assigned a group of people free from sleep disorders to be put on a 20-hour sleep-wake schedule, simulating a traveller crossing four time zones eastward every day. They were asked to take 0.3 or 5 mg of melatonin or a look-alike placebo pill 30 minutes before each scheduled sleep period, which lasted for 7 hours.

People who took melatonin had longer sleep time during the day when the body doesn't normally produce it, compared to those who took placebo, the study found out. But when they were given melatonin at night when the body produces its own melatonin, no added benefits were discovered.

Also, melatonin as a supplement seems to lift winter depression by resetting the circadian rhythms in people affected by Seasonal Affective Disorder (SAD).

The researchers assigned 68 SAD patients to take either low doses of melatonin or placebo in the morning or afternoon for one winter month. Then they analyzed their sleep activity, melatonin rhythms, and depression symptoms. The researchers had found out that melatonin had more antidepressant properties compared to placebo.

SAD happens when there is a delay in daily circadian rhythm due to the later winter dawn.

In addition to melatonin, getting enough morning sunlight works best to people with SAD.