What is melatonin, the sleep regulator? Does it have a role in cancer treatment or prevention?

Melatonin is a hormone secreted by the pineal gland in the brain. It is also produced by gastrointestinal organs, bone marrow, the eyes, white blood cells and skin. Circadian rhythm is the biological clock with which its main function, regulating sleep, works. It also helps regulate blood pressure and reduce oxidative stress.

Over the past 150 years, first lamps and then television, industrialization and modern life have significantly changed sleep habits established over thousands of years. Because of these and many other factors, sleep disorders have become a problem affecting many people. Efforts to understand and treat them brought attention to the hormone melatonin , one of sleep’s most important regulators. Melatonin levels have been found below normal in many sleep-related conditions.

Also called a neurotransmitter, a molecule enabling communication between nerve cells, this hormone is neither secreted by a single organ nor effective in only one target organ. It acts through receptors in various body cells.

Melatonin and cancer

Melatonin’s role in canceris among the most extensively researched topics. Nevertheless, melatonin has no established, clarified role in either cancer prevention or treatment.

The most recent studies on melatonin’s role in inhibiting tumor growth include:

• In 2016, a study published in Breast Cancer reviewed all studies over 20 years, concluding that “melatonin may inhibit cancer cell growth and blood vessel formation”, but further analyses were needed to confirm these studies.
• According to a study published in Genes and Cancer in 2016, melatonin was found to suppress breast cancer tumor growth. It is thought to bind estrogen receptors, preventing natural estrogen binding and thereby inhibiting tumor growth.

The above research consists of cell-culture studies; effects on actual human tumors have not yet been measured. Other laboratory cell-culture studies also reported possible antioxidant, immune-regulating and tumor-growth-inhibiting effects. Further analyses are needed to confirm these studies. In 2013, the United States National Cancer Institute stated that there was no convincing evidence for a cancer-preventive effect of melatonin use.

Melatonin’s role in treating cancer side effects

Clinical studies also examine its role in treating cancer side effects. These include:

• With 61 patients included across 8 randomized studies, statistical analysis reported that daily oral melatonin produced positive effects on disease course. However, more comprehensive studies with larger participant numbers are needed for statistical significance. No firm conclusion can be drawn from this study.
• Melatonin has been tried for cancer cachexia (involuntary weight loss), which may arise from cancer itself or treatment. Although early studies suggested possible benefits for cancer-related weight loss, larger studies failed to confirm this potential benefit.

The relationship between melatonin and cancer remains experimental and will take many years to clarify. Clinical studies remain early-stage and involve few patients. In conclusion, melatonin has no established role in cancer prevention or treatment and can only be considered within alternative medicine practices . Please do not take oral melatonin tablets for a cancer-related condition without consulting your doctor. 

Related topic:

- Does night-shift work or on-call duty increase cancer risk?