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Sleep and the Risk of Cancer

It’s very easy to see the effects of short sleep, shift change or restless non-restorative sleep. We feel daytime sleepiness and a lack of energy. Sadly, we don’t see the more adverse effects like changes in our genetic expression and hormonal imbalances.

Those two problems are likely to cause cancer in many people who suffer from sleep deprivation or work night shifts frequently. A very high number of recent studies shows a strong relationship between sleep and cancer. One has shown that women who work night shifts have a 50% higher chance of suffering from breast cancer. Numbers are also high for other cancer types like prostate, colorectal and thyroid cancer to name a few. The World Health Organization has listed night shifts as a possible carcinogen in 2007.

Not everybody with a poor sleep schedule develops cancer. That depends on your genetic predisposition, overall health and other factors like stress, smoking, drinking alcohol, etc. Sleep gives your body room and time to destroy damaged and cancerous cells. Cutting down on sleep or shifting the natural sleep rhythm is literally sabotaging your body’s functionality and health.

It is not dangerous if you sleep for 3 hours one night; although your body will fail to clear your brain and restore your cells. However, if you keep doing this over and over, your body keeps failing to perform the “maintenance” and the situation worsens. You run a high risk of developing cancer if this type of behavior continues for a decade or so.

Sleep and cancer: what happens in the body when we don’t sleep right?

Some really important processes get disrupted as a consequence of poor sleep. These include our circadian rhythm, hormone production, immune system, mood (stress levels) and more.

Circadian rhythm

Circadian rhythm is our body’s rhythm which depends on day and night time as well as our sleep habits. The circadian clock in the brain regulates cell activity and various bodily processes which keep us healthy and functional.

If someone’s sleep schedule is too unpredictable, his or her circadian rhythm can get out of tune and consequentially disrupt how our cells work, which means bad metabolism, weak immune system, gut microbiome imbalance and a better environment for cancer cell proliferation. Those who already have cancer run the risk of increasing cancer aggressiveness if they don’t ensure good sleep.


Melatonin is a hormone which is excreted in the evening and throughout the night. Melatonin makes us sleepy and plays an important role in the circadian rhythm. Some people who have circadian disturbances can solve their sleep problems by taking melatonin supplements. Melatonin is also a powerful antioxidant and an inhibitor of cancer cell growth. Low melatonin is found in people who suffer from prostate, breast and ovarian cancers.

Unfortunately, bright light exposure at night suppresses melatonin and disrupts the circadian rhythm as much as staying up late does. Melatonin intake hasn’t only shown an improvement in the circadian clock, but also in cancer treatment. Patients who take melatonin tolerate chemotherapy better and show a regression in tumor growth.

Blue light at night cancer diagram

Figure 1. How light affects melatonin and helps tumor growth. Source: Bill Lagakos

The immune system

The immune system is able to defend the body from illnesses when our sleep is sufficient and of good quality. Lack of sleep produces increased levels of inflammation. Cancer cells can get formed as a consequence of long-lasting inflammation. In fact, about a fifth of reported cancers is developed either directly or indirectly due to chronic inflammation.

Other problems

Stress and anxiety are increased by sleep deprivation. People also tend to become lonelier and more depressed. Stress aggravates one’s sleep and immunity and is linked with faster tumor growth and more aggressive forms of cancer.

Sleep deprivation and bright light also negatively reflect on insulin resistance and metabolism, increasing the possibility of becoming obese or diabetic. Obese patients usually have poor sleep, suffer from inflammation and are at a very high risk of developing cancer.

Does insufficient sleep increase the risk of developing cancer?

Regardless of its cause, insufficient sleep is closely related to cancer; many studies support this statement.

A study from 2013 has shown a strong association between prostate cancer, short sleep, and frequent wakings in older men. Higher sleep disturbances seem to produce worse cases of cancer.

Sleep duration and quality are also linked to breast cancer and its aggressiveness. Research suggests that African American women are three times more likely to develop breast cancer as a consequence of inadequate sleep than white women.

Are night-shift workers more likely to get cancer?

Employees who work in night shifts run a serious risk of developing cancer. The most dangerous situation is the one in which shifts rotate every week or two so workers’ circadian rhythms can never adjust to the sleep schedule.

Nurses, firefighters, airline workers and others who work the graveyard shift are at a worryingly high risk of colorectal, bladder, lung, breast, prostate and pancreatic cancers. Circadian disturbance and the lack of melatonin are the main suspects for this disease.

Sleep disorders and cancer

Insomnia (difficulty falling or staying asleep), obstructive sleep apnea (breathing difficulty which causes fragmented sleep), and other sleep disorders can increase the risk of cancer.

Sleep disorders usually result in undesirable sleep architecture, which means more light sleep and less deep restorative sleep. Poor quality sleep doesn’t offer immune system regulation, cell restoration, stress relief, and other benefits. This creates a bad environment which is good for the proliferation of cancerous cells.

Does too much sleep also cause cancer?

If you sleep more than 9 hours every day, you probably sleep too much. Oversleeping is as big of a problem as sleep deprivation. It has similar consequences as well. The poor immune system, obesity, and depression are some of the consequences.

Sleeping too much bears risks of liver and breast cancer.

How does sleep protect you from cancer?

Sleep provides your body with thorough restoration. It clears your brain, keeps heart and blood vessels healthy and kills any damaged or cancerous cells.

Actually, melatonin does this. So even if there was a bad cancerous cell in your body at some point, melatonin might have helped kill it, protecting you from cancer. If you constantly sleep well and follow a regular sleep schedule, your body will have plenty of chance to fix any problems.

Sleep well to lower the chances of developing cancer

Take good care of your sleep because it helps you stay healthy. Pay special attention to your circadian rhythm and night light exposure. It is advisable to go to bed and wake up at approximately the same time every day (including weekends and holidays). Other good sleep habits include ensuring a cool, dark and quiet environment, avoiding any technology, caffeine and big meals prior to bed.

Sleep can keep you safe from cancer. Even so, you should also refrain from other possible carcinogens like tobacco, alcohol and a sedentary lifestyle.

Additional resources

  1. Role of Melatonin in Cancer Treatment. http://ar.iiarjournals.org/content/32/7/2747.full
  2. Sleep Disruption Among Older Men and Risk of Prostate Cancer. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3652595/
  3. Sleep Quality, Duration and Breast Cancer Aggressiveness. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5488283/
  4. Sleep disturbance and incidence of thyroid cancer in postmenopausal women the Women’s Health Initiative. https://www.ncbi.nlm.nih.gov/pubmed/23221728
  5. Sleep duration and the risk of cancer: a systematic review and meta-analysis including dose-response relationship. https://www.ncbi.nlm.nih.gov/pubmed/30463535
  6. How Does Sleep Affect Our Cancer Risk? https://thesleepdoctor.com/2019/01/08/how-does-sleep-affect-our-cancer-risk/
  7. Night work and the risk of cancer among men. https://www.ncbi.nlm.nih.gov/pubmed/23035019
  8. Circadian Disruption, Shift Work and the Risk of Cancer: A Summary of the Evidence and Studies in Seattle. https://www.researchgate.net/publication/7184137_Circadian_Disruption_Shift_Work_and_the_Risk_of_Cancer_A_Summary_of_the_Evidence_and_Studies_in_Seattle