The Melatonin-Sleep-Cancer Connection

The Melatonin-Sleep-Cancer Connection

By Andrea Bartels CNP NNCP RNT
Registered Nutritional Therapist

02 Nov 2021

The Melatonin-Sleep-Cancer Connection

The connection between sleep and cancer risk is a complex yet important one. We know that regular, adequate amounts of quality sleep are vital for healthy immunity. But why? How? Studies show sleep deprivation reduces function of various immune cells necessary for destroying pathogens and cancer cells. So, even if you’ve never been diagnosed with cancer, it’s good to understand how good sleep may be vital to reducing your risk.

Sleep: a Major Factor in Immunity

Lack of sleep is bad for the immune system and good for cancer development.  Consider that the top cause of sleep deficiency is none other than STRESS. Stress initiates release of adrenaline and cortisol, which make falling asleep difficult because these two hormones are stimulating to the nervous and cardiovascular systems. Now consider that cortisol’s anti-inflammatory action is what categorizes it as an immune-suppressant. The resulting sleep-deprived, inadequate immune response by the cells that work to protect us from infectious agents and cancer development is a recipe for ill health.

The Protective Effects of Melatonin

Our circadian rhythm is a natural process that governs our sleep-wake cycle, and is influenced by our exposure to light and dark. When our eyes perceive a gradual reduction in daylight each evening, the pineal gland within the brain releases the hormone melatonin, making us sleepy enough to settle in for a full night of shut-eye.  But constant exposure to artificial lighting suppresses melatonin production and disrupts our circadian rhythm.  Think about how much time you spend indoors on the colder, shorter days of winter. Do you have more difficulty establishing a regular sleep-wake cycle now, compared to in summer months?

When it comes to certain types of cancer, a chronically irregular circadian rhythm appears to play a significant developmental role. Consider that melatonin sets this sleep-wake cycle, and is so important to immunity that it can also synthesized by the immune cells themselves.  This is interesting because according to research at Johns Hopkins University’s Kimmel Cancer Center, disruptions in circadian rhythm may raise the risk of cancer in the breast, colon, ovaries and prostate gland.

Sleep and Prostate Cancer

In prostate cancer research, it’s been observed that nations with higher levels of night-time light exposures have higher incidence of this cancer. Males who have never worked night shifts had a lower incidence of prostate cancer compared to those who are regular night shift workers.  In addition, men who complained of sleep difficulties had lower levels of melatonin metabolites in their urine and higher rates of prostate cancer.

Breast Cancer and Melatonin

When it comes to breast cancer, melatonin has been shown to improve the female’s immune response to fight a tumour. It inhibits tumor growth factor, decreases the ability of cancer cells to attach to basement membranes, reduces risk of invasive cancer, and regulates healthy cell division and multiplication.  Another way that melatonin appears to protect against estrogen-receptor-positive breast cancer in particular is by decreasing the number of estrogen-receptors in breast cells. While some of these impressive findings came from experiments outside the human body, consider the following observational findings in women:

In a study of 800 women, those who worked at least one night shift per week for at least three years, meaning they were often awake from 1 a.m. to 2 a.m.—when melatonin levels typically peak---had 60 percent more of the breast cancer cases compared to the control group who didn’t work nights.

In one comparative study conducted in the 1980s, a small study of profoundly blind women had just half the incidence of breast cancer as women who were not profoundly blind. 

A more recent Norwegian study of more than fifteen thousand visually-impaired women found that participants who were only mildly visually impaired had a higher incidence of breast cancer compared to those who were completely blind.  Since profoundly blind women have no ocular perception of light, their melatonin production is not suppressed by light exposure as it would be in seeing individuals. This fascinating research supports the ‘melatonin hypothesis’; that is, that visual perception of electric light reduces the production of melatonin by the pineal gland and therefore increases breast cancer incidence. 

Is the Night Shift Carcinogenic?

While it must be understood that most cancers have multiple causes, there is undoubtedly a large, ever-growing body of research on the subject of sleep quality, melatonin and their impact on cancer risk. Study after study has observed that workers who regularly work overnight in artificial light conditions for years tend to have reduced melatonin production, which encourages cancer to grow. There is so much research associating shift work with cancer that starting in 2007, The International Agency for Research on Cancer (IARC) has classified shift work itself as ‘carcinogenic’! In 2019, this classification was updated to specify ‘night shift work’ in order to reflect the relationship between cancer and low melatonin levels. 

The Easy Way to Increase Melatonin Levels

Sleep quality and duration hinges upon adequate melatonin release, which in turn affect cancer risk in the ways noted above. Supporting sleep therefore needs to be a priority if we want to stay well. Fortunately, while some of us have no choice but to work overnights, there is a simple and safe way to ensure adequate melatonin exposure: through supplementation. Pure Lab Vitamins’ Magnesium Glycinate with Melatonin capsules can be used to support those who have no choice but to sleep during the daylight hours when it’s difficult to guarantee conditions dark enough to make their own melatonin production.  With just 3 milligrams of melatonin per capsule, one can increase their dosage as needed to restore melatonin to the levels needed for healthy cell replication, immunity and deep sleep.  It is paired with magnesium glycinate to support one’s own melatonin production, and buffers any release of the stimulating neurotransmitters adrenaline, noradrenaline and dopamine when 1 to 3 capsules are used at bedtime.  





Besedovsky L, Lange T, Born J. Sleep and immune functionPflugers Arch. 2012;463(1):121-137.

Blask DE. Melatonin, sleep disturbance and cancer risk. Sleep Med Rev. 2009;13(4):257-264. doi:10.1016/j.smrv.2008.07.007

Carrillo-Vico A, Lardone PJ, Alvarez-Sánchez N, Rodríguez-Rodríguez A, Guerrero JM. Melatonin: buffering the immune system. Int J Mol Sci. 2013;14(4):8638-8683. Published 2013 Apr 22.

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;17(4):539-545.

European Society for Medical Oncology. Night Shift Work Classified as Probably Carcinogenic to Humans. Oncology News 10 Jul 2019. Accessed October 28th, 2021.

Glickman G, Levin R, Brainard GC. Ocular input for human melatonin regulation: relevance to breast cancer. Neuro Endocrinol Lett. 2002;23 Suppl 2:17-22.

Hakim F, Wang Y, Zhang SX, et al. Fragmented sleep accelerates tumor growth and progression through recruitment of tumor-associated macrophages and TLR4 signaling. Cancer Res. 2014;74(5):1329-1337.

Hahn RA. Profound bilateral blindness and the incidence of breast cancer. Epidemiology. 1991;2(3):208-210.

Hansen J. Night Shift Work and Risk of Breast Cancer. Curr Environ Health Rep. 2017;4(3):325-339.

Johns Hopkins Medicine. “Lack of Sleep and Cancer: Is There a Connection?” Accessed October 28th, 2021.

Kaur, Sat Dharam.  The Complete Natural Medicine Guide to Breast Cancer. Tobert Rose Publishing, 2003.

Kliukiene J, Tynes T and A Andersen. Risk of Breast Cancer Among Norwegian women with visual impairment. British Journal of Cancer 2001; 84(3); 397-399.

Lissoni P, Barni S, Tancini G, et al. Clinical study of melatonin in untreatable advanced cancer patients. Tumori. 1987;73(5):475-480.

Lissoni P, Barni S, Meregalli S, et al. Modulation of cancer endocrine therapy by melatonin: a phase II study of tamoxifen plus melatonin in metastatic breast cancer patients progressing under tamoxifen alone. Br J Cancer. 1995;71(4):854-856. doi:10.1038/bjc.1995.164

Napoli, M. Exposure to light at night increases the risk of breast cancer. Health Facts, Nov. 2001, 26 (11); 3-4.


Blog Post Image

Support for Seasonal Affective Disorder


Blog Post Image

Immune support and Respiratory Illnesses


Replenish Your Body

See how you can benefit from our unique line of products.

Find a Store

Find our products at your nearest PLV retailer.