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Melatonin may help regulate the timing and release of female reproductive hormones by determining when menstruation begins, the frequency and duration of menstrual cycles, and when menstruation ends (menopause).

It is believed that melatonin is directly related to the aging process. Young children exhibit the highest levels of nighttime melatonin. As we age our melatonin levels diminish and may explain why older adults have disrupted sleep patterns and tend to go to bed and wake up earlier than when they were younger.

In addition to its hormonal actions, melatonin has strong antioxidant effects and can help strengthen the immune system.

Insomnia Although results are still controversial, studies suggest that melatonin supplements help induce sleep in people with disrupted circadian rhythms (such as those suffering from jet lag or poor vision or those who work the night shift) and those with low melatonin levels (such as some elderly and individuals with schizophrenia). In fact, a recent review of scientific studies found that melatonin supplements help prevent jet lag, particularly in people who cross five or more time zones.

A few studies suggest that when taken for short periods of time (days to weeks) melatonin is significantly more effective than a placebo, or “dummy pill,” in decreasing the amount of time required to fall asleep, increasing the number of sleeping hours, and boosting daytime alertness. In addition, at least one study suggests that melatonin may improve the quality of life in people who suffer from insomnia and some experts suggest that melatonin may be helpful for children with learning disabilities who suffer from insomnia.

Osteoporosis
Melatonin has been shown to stimulate cells called osteoblasts that promote bone growth. Since melatonin levels may be lower in some older individuals such as postmenopausal women, current studies are investigating whether decreased melatonin levels contribute to the development of osteoporosis, and whether treatment with melatonin can help prevent this condition.

Menopause
Melatonin supplements may benefit menopausal women by promoting and sustaining sleep. Peri- or postmenopausal women who use melatonin supplements to regulate sleep patterns should do so only for a short period of time since long term effects are not known.

Depression
A recent study of postmenopausal women found that melatonin alleviated both depression and anxiety. Other studies show that people who suffer from major depression or panic disorder have low levels of melatonin. Healthy individuals with mild episodic depression and patients who have Seasonal Affective Disorder, (SAD -- a mild depression that correlates with fall and winter -- periods of light-phase shortening) also have lower than normal melatonin levels. Experimental studies show that melatonin causes a surge in the chemical serotonin, which helps alleviate symptoms of depressive illness, including major and mild depression and SAD. Melatonin should be used with caution in people with depression and should be appropriately timed with light therapy and sleep-phase changes. Disruption of normal circadian rhythm by poorly timed melatonin administration may worsen depression.

Eating Disorders
Melatonin levels may play a role in the symptoms of anorexia. For example, abnormally low melatonin levels may cause depressed mood in people with this condition. However, researchers do not know whether supplementation will change the course of the disease. Some researchers speculate that low melatonin levels in people with anorexia may indicate who is likely to benefit from antidepressant medications (a treatment often used for eating disorders).

Breast Cancer
Several studies indicate that melatonin levels may be linked with breast cancer risk. For example, women with breast cancer tend to have lower levels of melatonin than those without the disease. In addition, laboratory experiments have found that low levels of melatonin stimulate the growth of certain types of breast cancer cells, while adding melatonin to these cells inhibits their growth. Preliminary laboratory and clinical evidence also suggests that melatonin may enhance the effects of some chemotherapy drugs used to treat breast cancer. In a study that included a small number of women with breast cancer, melatonin (administered 7 days before beginning chemotherapy) prevented the lowering of platelets in the blood. This is a common complication of chemotherapy, known as thrombocytopenia that can lead to bleeding.

Prostate Cancer
Like breast cancer, studies show that people with prostate cancer have lower melatonin levels than men without the disease. Melatonin blocks the growth of prostate cancer cells in test tube studies. In one small-scale study, melatonin (when used in combination with conventional medical treatment) improved survival rates in 9 out of 14 patients with metastatic prostate cancer. Interestingly, since meditation may cause melatonin levels to rise it appears to be a valuable addition to the treatment of prostate cancer. More research is needed before doctors can make recommendations in this area.

Cancer-related Weight Loss
Weight loss and malnutrition are concerns for people with cancer. In one study of 100 people with advanced cancer, those who received melatonin supplements were less likely to lose weight than those who did not receive the supplements.

Sarcoidosis
Some physicians use melatonin to help treat sarcoidosis (a condition where fibrous tissue develops in the lungs and other tissues). Two case reports suggest that melatonin may be helpful for those who do not improve from conventional steroid treatment.

Rheumatoid Arthritis
Melatonin levels are lower in patients with rheumatoid arthritis than in healthy individuals without arthritis. However, when arthritis patients were treated with the anti-inflammatory medication indomethacin, melatonin levels returned to normal. The chemical structure of melatonin resembles indomethacin, so researchers suspect that melatonin supplements may work similarly to this medication for people with rheumatoid arthritis. However, this theory has not been tested.

Attention Deficit/Hyperactivity Disorder (ADHD)
Although melatonin supplementation does not appear to improve the key behavioral symptoms of ADHD, it may be effective in managing sleep disturbances in children with this condition.

Epilepsy
Preliminary research suggests that melatonin reduces the number of seizures in certain animals and may reduce seizures in people with epilepsy. However, not all experts agree with these findings. In fact, some researchers are concerned that melatonin (1 to 5 mg per day) may actually induce seizures, particularly in children with neurologic disorders. Since this research is in the early stages, some experts suggest that doctors should administer melatonin only to a select group of people who suffer from seizures that cannot be controlled by any other type of therapy.

Sunburn
A few small studies suggest that gels, lotions, or ointments containing melatonin may protect against redness (erythema) and other skin damage when used alone or in combination with topical vitamin E prior to exposure to UV radiation from the sun.

Viral Encephalitis
Although melatonin has not been scientifically evaluated for use in treating human encephalitis (inflammation of the brain), some studies suggest that this supplement may protect animals from serious complications associated with the condition and even increase their survival rates. In one study of mice infected with Venezuelan equine virus (a type of organism that causes viral encephalitis), melatonin supplements significantly lowered the presence of virus in the blood and reduced death rates by more than 80%. More studies are needed to determine whether similar treatment may offer the same protection to people with viral encephalitis.

Heart Disease
Low blood levels of melatonin are associated with heart disease, but it is not clear whether melatonin levels are low in response to having heart disease or if low levels of melatonin cause people to develop this condition. In addition, several animal studies suggest that melatonin may protect the heart from the damaging effects of ischemia (decreased blood flow and oxygen that often leads to a heart attack). However, researchers are unclear whether melatonin supplements may help prevent or treat heart disease in people. More studies are needed before scientists can draw any conclusions.