Low Melatonin Levels May Increase Breast Cancer Risk In Women!

Low melatonin levels may result in a lot more than just getting a lousy night’s sleep. Melatonin is the hormone produced by the pineal gland that regulates our circadian rhythms (also called bio-rhythms) and sleep cycle. When we stay up super late, travel across time zones or work the night shift, the normal circadian cycle is disrupted. New studies are showing that this disruption can result in impaired immune function, and a higher risk of certain types of cancer. The good news is that studies also show that optimal levels of melatonin can help prevent certain cancers.12

Individuals who work the graveyard shift (starting work after 7:00 PM and leaving before 9:00 AM) and are exposed to light at night on a regular basis experience circadian disruption including melatonin suppression and sleep disturbances. Sleep disturbances can lead to immune suppression and a shift to the predominance in cancer-stimulatory cytokines.*3

* (A cytokine is a small protein released by cells that has a specific effect on the interactions between cells and on the behavior of cells. The bad cytokines trigger inflammation and are involved in almost every disease. But they can be suppressed with the right diet, life style and nutritional supplements such as vitamins D, E, Omega-3 fatty acids, grape seed extract and curcumin.)

In 2007 The International Agency for Research on Cancer (IARC), part of the World Health Organization, concluded that night work is “probably carcinogenic to humans.” Epidemiological studies have found that long-term night-workers have a higher risk of breast cancer.

These studies have involved mainly nurses and flight attendants and are consistent with animal studies that demonstrate that constant light, dim light at night, or simulated chronic jet lag can substantially increase tumor development. Other experimental studies show that reducing melatonin levels at night increases the incidence of tumor growth.4

Two studies suggest that women who work the night shift may have a small increased risk of developing breast cancer, possibly because prolonged exposure to light at night interferes with the body’s production of melatonin, which might increase estrogen levels.

In a case-control study the researchers interviewed 813 women who had been diagnosed with breast cancer between 1992 and 1995, and a control group of 793 women who did not have breast cancer. Among women who did not sleep during the hours when melatonin production is usually highest, there was a 14% increase in risk for each day of non-peak sleep per week. Working the graveyard shift for at least one day per week over a period of at least three years, increased risk by 60%.5

A cohort study used data from the Nurses’ Health Study, which surveys a cohort of more than 100,000 nurses on a range of health issues. For this study, the researchers followed up on 78,562 of the nurses who answered a question on night work in the 1988 survey. The increased breast cancer risk found in the study was restricted to a small group of women: those who worked 30 or more years on rotating night shifts—only 1.8% of all women in the study population.6

Thanks to new research, we’re beginning to get a clearer understanding of how low levels of melatonin can result in breast cancer. Scientists at Tulane University have found that in animal models and human breast tissue melatonin suppresses the development and growth of breast cancer by regulating growth factors and gene expression, inhibiting tumor cell growth, and even regulating the development of mammary glands in laboratory animal models.78

Older studies have suggested that low melatonin levels influence different stages of cancer progression in brain tumor, colorectal, endometrial and prostate cancer, but more studies need to be done on humans.


  1. Ruiz-Rabelo JF, Vázquez R, Perea MD, Cruz A, González R, Romero A, Muñoz-Villanueva MC, Túnez I, Montilla P, Muntané J, Padillo FJ. Beneficial properties of melatonin in an experimental model of pancreatic cancer. J Pineal Res. 2007 Oct;43(3):270-5.
  2. Martínez-Campa C, Alonso-González C, Mediavilla MD, Cos S, González A, Ramos S, Sánchez-Barceló EJ. Melatonin inhibits both ER alpha activation and breast cancer cell proliferation induced by a metalloestrogen, cadmium. J Pineal Res. 2006 May;40(4):291-6.
  3. Blask DE. Melatonin, sleep disturbance and cancer risk. Sleep Med Rev. 2009 Aug;13(4):257-64. Epub 2008 Dec 17.
  5. Davis S, Mirick DK. Circadian disruption, shift work and the risk of cancer: a summary of the evidence and studies in Seattle. Cancer Causes Control. 2006 May;17(4):539-45.
  6. Schernhammer ES, Hankinson SE. Urinary melatonin levels and postmenopausal breast cancer risk in the Nurses’ Health Study cohort. Cancer Epidemiol Biomarkers Prev. 2009 Jan;18(1):74-9.
  7. Hill SM, Frasch T, Xiang S, Yuan L, Duplessis T, Mao L. Molecular mechanisms of melatonin anticancer effects. Integr Cancer Ther. 2009 Dec;8(4):337-46.
  8. Blask DE, Dauchy RT, Brainard GC, Hanifin JP. Circadian stage-dependent inhibition of human breast cancer metabolism and growth by the nocturnal melatonin signal: consequences of its disruption by light at night in rats and women. Integr Cancer Ther. 2009 Dec;8(4):347-53.