Melatonin in Cancer Prevention and Treatment

Though melatonin is a hormone that the brain produces naturally, you might know it better as an over-the-counter remedy for jet lag and sleep disturbances. The brain’s pineal gland secretes melatonin in a 24-hour cycle. It's also produced in the skin, the retina of the eye, and the bone marrow.

In nature, the production of melatonin peaks at nighttime, and it's inhibited by the light of day. With darkness comes increasing levels of melatonin, bringing on lethargy and calm—and hopefully, sleep. Other factors and hormones such as serotonin are also important, however, in regulating the body’s sleep-wake cycles.

Sleep, Melatonin, and Cancer

Studies showing connections between poor sleep, low melatonin levels, and cancer have spurred a great deal of interest. Nighttime shift work is linked to fatigue and insomnia, lower levels of melatonin in the blood, and many different illnesses including heart disease, metabolic syndrome—and cancers of various types.

Shift Work and Cancer Risk

All of these findings in shift workers led some scientists to wonder whether melatonin might help to protect people from these illnesses. One Canadian study in male shift workers found that night work was associated with greater odds of a variety of different cancers, including non-Hodgkin lymphoma.

These kinds of studies look to see how common something is relative to something else—they are "cross-sectional," or so-called epidemiological in nature. Data from similar studies seem to hint at a possible role for melatonin and sleep disruption in breast cancer as well: women who work the night shift have a 19 to 51 percent increased risk of breast cancer.

With regard to prostate cancer, one study found that men with cancer of the prostate had lower melatonin levels compared with men who had the noncancerous but potentially sleep-disrupting condition, benign prostatic hyperplasia.

None of these studies are the type that can show cause and effect, however. Findings serve to fuel additional studies, but they do not necessarily support the use of melatonin to prevent cancer.

Animal and Laboratory Data

Laboratory studies suggest that melatonin is a powerful antioxidant that also stimulates some parts of the immune system, but it's not known if this effect occurs in human beings.

Melatonin seems to inhibit some cancer cells from growing when it is directly applied to these cells in laboratory dishes and in animal studies—this effect has been seen in breast cancer and melanoma.

Studies in humans, however, do not suggest any anticancer effect. Based on the in vitro data, some scientists have reasoned that immune stimulation, if present in vivo, might not be a good thing in all cases.

For instance, the wrong kind of immune stimulation in patients with leukemia or lymphoma could theoretically be counter-productive, since these cancers involve malignancy of immune cells in the lymph system, bone marrow, and blood.

Melatonin in experimental models has shown some anti-cancer properties, and stimulation of the immune system is thought to be involved. A study by Miller suggested that melatonin participates in the activation of lymphocytes and monocytes/macrophages—different types of white blood cells. Lymphomas are cancers that arise from the lymphocytes.

In vitro, melatonin seems to act in the augmenting of natural killer T-cell activity, stimulating certain cell signals called cytokines; it may also protect some blood cell precursors from the toxic effect of chemotherapy and radiotherapy, according to a 2001 study by Maestroni. Again, it is not known whether melatonin would have this effect in vivo, in real patients.

Melatonin in Cancer Treatment

Much less is known about melatonin when used in people who have cancer. One group of scientists systematically reviewed the effects of melatonin when given together with chemotherapy, radiotherapy, supportive care, and palliative care in patients with metastatic solid tumors—not leukemia or lymphoma. In this study, melatonin was not associated with added toxicity or reduced treatment efficacy, and it seemed to help with some chemotherapy side effects.

Melatonin in Blood Cancer Patients

Even less is known when it comes to melatonin in people with blood cancers like leukemia and lymphoma. Current National Comprehensive Cancer Network (NCCN) guidelines on non-Hodgkin lymphomas, the most common type of lymphoma, do not include recommendations on melatonin use.

The bulk of currently published research on melatonin that's in any way related to lymphoma seems to come from in vitro and animal data, not clinical trials. Always talk to your healthcare provider about taking any supplements, as supplements can have adverse effects and drug interactions.

A Word From Verywell

Melatonin has been used safely as a sleep aid by many and has an established role in the treatment of a variety of sleep disturbances.

Melatonin is a natural product, but natural products can still have side effects and unanticipated interactions. Melatonin may interact with a variety of medications, including sedatives, antidepressants, hormonal medications, and others.

Talk to your healthcare provider about your use of melatonin or any other supplement—especially if you are being treated for cancer or any other chronic illness.