5 Important Connections Between Cancer and Sleep

Part 1: Some things to know about your sleep and cancer risk.

Posted Nov 14, 2019

Deposit Photos
Source: Deposit Photos

In the first part of my series on sleep and cancer, I talked broadly about the risks that poor quality and disrupted sleep can have on our risk for the disease. Here, I’ll dig in a little deeper, to look at some of the different pathways and mechanisms by which sleep might affect our risk for developing cancer.

Some of these may surprise you. For example, a lot of my patients are startled to learn that melatonin, a hormone that’s so strongly aligned with sleep, has an impact on how cancer cells grow.

Cancer remains one of the most frightening and difficult diseases of our time. Sleep can play a powerful and protective role in helping us manage and even reduce our cancer risk. It’s my hope that the more you understand about the different ways sleep may affect cancer, the more attention you’ll give to your sleep every day.

Let’s jump in and explore the connections between sleep and some of the major underlying factors that drive cancer development. 

Circadian rhythms 

How circadian rhythms relate to sleep: Sleep is one of the many physiological functions that’s regulated by circadian rhythms, the 24-hour daily biorhythms that govern so many of our physiological processes. When people experience trouble with sleep—in particular, when sleep disruptions are chronic—often, circadian rhythm disruption is an underlying cause.

Our circadian rhythms and the clocks that regulate them are sensitive and finely tuned. Our bio clocks are affected most significantly by exposure to light (and to its absence, darkness). But circadian rhythms are also affected by our eating patterns, and as research suggests, by the makeup and activity of our gut microbiome. Other factors that affect circadian rhythms include stress and environmental factors such as toxins and pollutants.

When we sleep on irregular schedules—going to bed and waking up at drastically different times from one day or one week to the next, it can contribute to strain and disruption on our circadian clocks. Light exposure at the “wrong” times, particularly in the evening and overnight hours when we’d naturally be immersed in darkness, also pushes circadian rhythms out of sync. When we’re active at times when the body is biologically programmed to sleep—such as overnights, evenings, and early mornings—that also disrupts circadian function. Disrupted circadian rhythms don’t only make sleep harder to get and less refreshing. They affect a whole range of biological functions.

How circadian rhythms relate to cancer: Circadian rhythms are governed by a master circadian clock that’s located in the brain, which in turn coordinates the timing of “peripheral” circadian clocks throughout the body, including in every one of our cells. Among the responsibilities of our circadian system is to regulate cellular function, including cell repair, growth, and division. Several genes—including the PER 1, 2, and 3 genes and CRY 1 and 2 genes—work to regulate the synchronicity and activity of our circadian rhythms and of cell behavior itself. Among other factors, sleep deprivation has been shown to alter the activity of circadian clock genes.

Research strongly indicates that disruptions to circadian rhythms cause abnormal behavior in cells that can lead to the development of cancer, and to more aggressive growth in cancer cells. Dysfunction in the behavior of key circadian genes appears to be one possible root cause of this abnormal cellular behavior, driving abnormal cellular activity that can lead to cancerous cell proliferation. Changes to the activity of circadian genes have been linked to breastprostatebrainleukemia and non-Hodgkin’s lymphoma, as well as other forms of cancer. Circadian rhythm disruptions are thought to be one reason why shift workers are at greater risk for cancer, and why shift work has been identified as a likely carcinogen by the World Health Association.

Circadian rhythm dysfunction may affect cancer risk through a number of mechanisms. Our biorhythms govern immune function, metabolism, hormone activity and other key biological processes that affect cell function and potential development of cancer. There’s a tremendous amount still to learn about the relationship between circadian function and cancer, but we may discover it is a fundamental


How melatonin relates to sleep: Melatonin is often referred to as “the sleep hormone” or “the darkness hormone,” and is probably best known as a natural promoter of sleep. (Many people use supplemental melatonin to help sleep.)

Like many of the body’s hormones, melatonin follows a daily circadian rhythm, adhering to a 24-hour cycle of rising and falling production. Melatonin doesn’t only follow circadian rhythms—its daily rise and fall also help to keep circadian clocks in sync. 

Melatonin delivers important cues to circadian clocks that keep them functioning properly. This sleep- and circadian-rhythm-regulating hormone is naturally suppressed by light and triggered by darkness. Melatonin production naturally increases in the evenings and levels typically hit a peak around 3-4 a.m., before falling to their daily lows around midmorning. The evening rise in melatonin makes us feel less alert, more relaxed, and more inclined to sleep.

Healthy sleep habits and routines include practices that keep melatonin production in sync and on schedule, and avoid outside influences that throw natural melatonin’s daily cycles off course. Avoiding light exposure in the evenings is the biggest step we can take to prevent suppression of melatonin, and disruptions to sleep and circadian rhythms.

How melatonin relates to cancer: Though best known as a sleep promoter, melatonin has many functions in the body beyond facilitating sleep. And many of these functions have implications for cancer. Melatonin keeps circadian rhythms functioning well. It helps to regulate the immune system. Melatonin acts as an antioxidant. It helps to control and to inhibit cell division. It also inhibits the growth of new blood vessels (including in cancer cells).

Melatonin is now recognized as having significant protective effects against cancer. Research indicates that melatonin is an inhibitor of cancer cell growth. Studies show that low levels of melatonin are associated with increased risk for several different types of disease, including prostate and breast, endometrial, and ovarian cancers. One recent study found men with low melatonin levels had a four times greater risk of prostate cancer. Melatonin has anti-estrogenic effects—it is involved in lowering estrogen levels and reducing estrogen-related activity in the body. Estrogen is involved in the development of some forms of breast cancer, as well as ovarian and endometrial cancers.

Melatonin is being investigated and used in the treatment of several forms of cancer. I’ll talk more about how melatonin is being used as a cancer fighter in an upcoming article.

Sweet Dreams,

Michael J. Breus, Ph.D., DABSM

The Sleep Doctor™