Melatonin is a hormone that communicates information concerning current light conditions to various parts of the body and plays a crucial role in the synchronization of circadian rhythms (body clocks). Melatonin is synthesized and secreted by the pineal gland in the brain. Women can maintain their melatonin levels by getting enough sleep, avoiding night shift work and light exposure at night, and consuming melatonin-rich foods such as cherries (especially sour or tart cherries), and tomatoes. Note that safe and effective dosages of melatonin supplements for breast cancer survivors have not been established.

Disruption of melatonin production is associated with increased risk of breast cancer. For example, long-term night shift work is a risk factor for breast cancer—the risk is highest for women working the most disruptive shifts. Light in the bedroom at night is also associated with increased risk of breast cancer, presumably because it interferes with melatonin production. While melatonin is known primarily for helping to regulate circadian rhythms, it has also been shown to have direct anticarcinogenic properties, especially in breast cancer. Now a new study has reported that melatonin enhances the treatment effects of radiotherapy in hormone receptor positive (ER+/PR+) breast cancer cells.

Anti-cancer activities of melatonin

Melatonin has been shown to have a variety of chemopreventive and chemotherapeutic activities. Melatonin influences the expression of genes involved in cell proliferation, immune responses, cell adhesion, apoptosis (programmed cell death), cell cycle and angiogenesis in ways that have anticancer effects in breast cancer cells. For example, melatonin induces the expression of tumor suppressor genes. Melatonin also stimulates the differentiation of fibroblasts and decreases aromatase expression and aromatase activity, thereby reducing the number of estrogen-producing cells near malignant cells.

Latest research finds melatonin enhances effects of radiotherapy

The study referenced at the beginning of this news article was designed to investigate the effects of a combination of radiation treatment and melatonin on hormone receptor positive breast cancer cells. To conduct the study, the authors compared the impact of melatonin (at various concentrations), radiation, and the combination of melatonin plus radiation on ER+/PR+ MCF-7 breast cancer cells. Melatonin alone was found to significantly inhibit proliferation of the cells at all concentrations tested. Radiation alone also inhibited cell proliferation and did so in a dose-dependent manner.

When breast cancer cells were pretreated with melatonin one week before radiation was applied, the reduction in proliferation was significantly greater than that produced by radiation treatment alone. Melatonin pretreatment also interfered with progression of the cell cycle in ways that reduced cell survival. Radiation alone reduced the expression of two important proteins involved in double-strand DNA break repair; pretreatment with melatonin for seven days before radiation led to a even larger reductions in these proteins. The authors conclude that pretreatment with melatonin before radiation sensitizes breast cancer cells to the treatment effects of radiation by inhibiting proliferation, inducing cell cycle arrest, and down-regulating proteins involved in DNA repair. The study findings may justify further investigation with clinical trials combining melatonin and radiotherapy, according to the authors.

Please see our article on what to eat during radiation treatment for more information.