Cancer is a major burden on public health worldwide. It is estimated that around 21% of men and 18% of women will be diagnosed with cancer at some point during their life. Those daunting figures are only expected to rise as the population increases and gets older.
Cancer occurs when cells grow abnormally and invade other tissue in the body. It is not a singular disease; instead, different types of cancer can have distinct causes, symptoms, and impacts on health.
As knowledge has grown about sleep’s integral role in overall health, many sleep scientists have turned their attention to how sleep and cancer are connected.
Though more research is needed, experts have uncovered a multifaceted relationship. Sleeping problems may be a risk factor for developing certain types of cancer. They may also affect the progression of cancer and the effectiveness of treatment.
In addition, cancer can affect sleep. Symptoms of cancer or side effects of treatment may cause sleeping problems, reducing quality of life in people with the disease. Cancer can also lead to lasting physical and mental changes that hinder sleep, including in cancer survivors who have long completed treatment.
Knowing about the complex relationships between cancer and sleep creates opportunities to improve health. Although it’s impossible to eliminate cancer risk, getting good sleep may be a protective factor. For people with cancer, better sleep may help in feeling better both physically and emotionally, improving their ability to cope with cancer.
Some of the systems that may be influenced by sleep in ways that affect cancer risk include the brain, the immune system, the production and regulation of hormones, and metabolism and body weight. Sleep may affect how cells function, altering their environment or the signals that affect how they grow.
While this is still an evolving field of research, the following sections provide an overview of current science about sleep’s potential impacts on cancer risk, progression, and treatment.
Any person who is concerned about their sleep or cancer risk should talk with their doctor to understand how this information applies in their specific situation.
Evidence has emerged that different components of sleep — sleep duration, sleep quality, circadian rhythm, and sleep disorders — can affect cancer risk. That said, studies on this topic are not always consistent or conclusive, which may reflect difficulties in accurately gathering data about sleep over the long term.
Studies about the effect of sleep duration on cancer risk have often been conflicting. Differences in results may relate to how sleep data is collected, the types of cancer considered, and how other factors that can influence cancer risk are accounted for.
Research has found that people who sleep less than six hours per night have a higher risk of death from any cause, and one large-scale study found that people with short sleep have an increased cancer risk.
For specific types of cancer, short sleep duration has been associated with a greater risk of colon polyps that can become cancer. In older adults, some research has tied reduced sleep duration to a higher likelihood of stomach cancer and found potential correlations with Non-Hodgkin Lymphoma as well as cancers of the thyroid, bladder, head, and neck.
These studies, though, are far from definitive. Many types of cancer, including lung cancer, have not been found to be affected by short sleep in other studies. Some research has even found fewer cancer cases in people sleeping less than seven or eight hours per night.
In animal studies, sleep deprivation has been connected to greater “wear and tear” on cells, potentially leading to the type of DNA damage that can give rise to cancer. Although this has not been definitively found in human studies, it provides a theoretical way that sleep and cancer may be connected.
In addition, insufficient sleep may indirectly heighten cancer risk. Insufficient sleep has been strongly linked to obesity, which is an established risk factor for many types of cancer. Lack of sleep is related to immune system issues like persistent inflammation, which is believed to raise cancer risk.
Researchers have also looked at long sleep duration, usually defined as sleeping more than nine hours per night, and found potential links to cancer risk. This amount of sleep was found in one study to elevate the risk of colorectal cancer in older adults, especially those who were overweight or snored frequently. Long sleep duration has been associated with an increase in risk of primary liver cancer and breast cancer, in particular the subtype in which growth is driven by estrogen.
Sleep quality is often even more difficult to accurately measure than sleep duration, especially over the long-term, which can make it challenging to clearly determine its effects on cancer risk.
In studies with mice, fragmented sleep triggered types of inflammation that promoted tumor growth and progression. In people, an observational study of over 10,000 adults over age 50 found a higher cancer risk in people who rated their sleep quality as intermediate or poor.
Another observational study involving over 4,000 women found an association between restless sleep and triple-negative breast cancer, an aggressive form of the disease. In a smaller study, men who suffered from sleep disruptions had a greater risk of developing prostate cancer with the highest risk among those with the most pronounced sleep interruptions.
As with sleep duration, more research is needed to replicate and verify these results. Future research may help identify how specific elements of sleep quality, such as the number or length of sleep interruptions, affect the likelihood of developing particular types of cancer.
Circadian rhythm is the body’s internal clock that spans a 24-hour day. It is controlled by a specific part of the brain called the suprachiasmatic nucleus (SCN), which sends signals throughout the body to optimize activity based on the time of day.
Light is a key driver of circadian rhythm, which is why, when not exposed to artificial light, people quickly adjust to a schedule of being awake during daylight hours and asleep when it’s dark. In modern society, though, constant artificial light, night shifts at work, and rapid travel across time zones can cause an individual’s circadian rhythm to be misaligned with natural daylight hours.
A growing body of evidence indicates that circadian disruption can play a role in the development of cancer. Circadian signals are involved in how cells grow and divide with implications for how mutations and DNA damage can occur. Hormone production and metabolism as well as immune function are subject to circadian influence and can be disturbed by a misaligned circadian rhythm.
The far-reaching influence of circadian rhythm on these bodily systems means that circadian disruption involves multiple potential links to the development of cancers, including breast cancer as well as cancer of the liver, colon, lung, pancreas, and ovaries.
Working at night, known as shift work, is often a cause of circadian misalignment, and shift workers have been found to have an elevated risk of cancer. The International Agency for Research on Cancer (IARC) has reviewed the existing evidence and determined that shift work is “probably carcinogenic” .
Some researchers have suggested that there may be interactions between circadian rhythm and exposure to carcinogens with the possibility that disrupted circadian timing could increase susceptibility to other risk factors.
Analysis of the relationship between sleep disorders and cancer has focused primarily on obstructive sleep apnea (OSA). OSA involves repeated pauses in breathing that create fragmented sleep and reduce the amount of oxygen in the blood, a condition known as hypoxia.
In animal research, persistent sleep interruptions and hypoxia from sleep apnea have been found to create conditions for accelerated tumor growth. In humans as well, several effects of sleep apnea are believed to generate an environment conducive to cancer.
These worrisome effects, including alterations to immune function, chronic low-grade and systemic inflammation, oxidative stress, and fragmented sleep, are magnified by hypoxia, which is suspected to reprogram some immune system cells in ways that make them less effective in attacking cancer cells. Areas of low oxygen are found within many types of tumors, which may mean that hypoxia-induced by sleep apnea can contribute to cancer risk.
Despite these biological mechanisms for a link between OSA and cancer, studies have not found universally consistent results about OSA as a risk factor.
Several large, long-term studies of people with OSA in both the U.S. and Spain have indeed detected an increased risk of death from cancer in people with moderate and severe OSA. Smaller studies have uncovered associations between OSA and breast cancer. Severe OSA has been linked with a heightened risk of cancers of the prostate, uterus, lung, thyroid, and kidney as well as malignant melanoma.
Nevertheless, not all researchers have identified the same patterns of cancer risk or mortality in people with OSA, and a few studies have even found fewer cancer cases in people with OSA. Discrepancies in research may relate to distinct ways of measuring OSA, limited data about which patients were receiving treatment for OSA, and the fact that OSA has links to other conditions, such as heart problems, obesity, and diabetes, that may also alter cancer risk.
Sleep may play a role in the progression of cancer and its growth over time. Some of the factors related to cancer risk, such as the impact of sleep on hormones, metabolism, and inflammation, may affect cancer’s aggressiveness, but additional research is necessary to clarify this potential connection.
In women with breast cancer, one study found that sleeping more than nine hours a night was correlated with a higher risk of death from breast cancer and all other causes. Another study found that sleep that was misaligned with circadian rhythm was tied to a faster recurrence of breast cancer after initial treatment.
A study looking at sleep and colorectal cancer showed that people who had short sleep duration before their diagnosis had an increased risk of cancer mortality, but this, like many studies, established only a correlation and not causation.
Obstructive sleep apnea is also believed to have a potential role in cancer progression because hypoxia and sleep fragmentation may enable tumors to more easily metastasize to other parts of the body.
A cancer patient’s sleep may influence their response to cancer treatment, and a deeper understanding of circadian rhythm may create possibilities for more effective cancer therapies.
Because the process of cell growth and division is affected by circadian rhythm, cancer cells may be more vulnerable or resistant to treatments depending on when treatment is given. Cancer drugs often target specific proteins, enzymes, or receptors on the surface of cells, and most of these are affected by circadian timing.
Though still developing, chronotherapy is a component of cancer treatment that works to optimize radiation therapy, chemotherapy, or immunotherapy based on a person’s circadian rhythm. Some researchers hope that chronotherapy can enable treatments to kill more cancer cells while reducing damage to healthy tissue.
Entirely new drugs may also be developed that seize upon knowledge of circadian rhythm to fight cancer. For example, drugs have been identified that manipulate the “on/off” signals for cell growth that are part of circadian timing, and early-phase studies have shown positive results for several types of cancer.
Sleeping well may affect the way that cancer patients recover and respond to treatment. For example, poor sleep has been connected to higher levels of pain, longer hospital stays, and a greater chance of complications in women undergoing surgery for breast cancer.
Research about obstructive sleep apnea and cancer indicates that the condition may make certain cancer treatments less effective. Some types of chemotherapy and radiation therapy have the greatest effect when oxygen levels in the tumor tissue are high, so hypoxia from disrupted breathing may prevent these treatments from working optimally.
Does Sleeping With a Light on Increase Cancer Risk?
Though not conclusive, some research indicates that exposure to artificial light at night may have an effect on cancer risk.
Darkness is an important contributor to circadian rhythm; it induces the body to produce melatonin, a hormone that facilitates sleep. Beyond its sleep-promoting benefits, melatonin has been found in animal studies to fight tumor growth and help repair DNA damage in cells. Theoretically, then, sleeping with the lights on may interfere with normal circadian signals and create conditions more permissive of cancer development .
In an observational study of people and their artificial light exposure at night, sleeping in a highly illuminated bedroom was associated with an elevated risk of prostate cancer but a decreased risk of breast cancer. Given these inconsistent findings, considerably more research is needed about light during sleep to determine whether or not it is a significant risk factor for cancer.
Can You Get Cancer by Sleeping Next to Your Phone?
There is no evidence that sleeping next to your phone increases your risk of cancer. The type of energy from cell phones, called non-ionizing radiation, does not cause DNA damage; instead, it’s only established biological effect is heating. Studies of cell phone users have not found any consistent pattern of elevated risk of brain tumors or any other kind of cancer.
Even though there is no clear link between cell phones and cancer, some experts recommend against keeping your phone right next to your head for prolonged periods of time. For that reason, it may be best to keep your phone on a nightstand or in a drawer.
In addition, while it is not known to cause cancer, technology in the bedroom can cause sleep disruptions, so it may help your sleep if you don’t bring your phone to bed with you.
Does Sleeping With a Bra Cause Breast Cancer?
Sleeping with a bra is not a risk factor for cancer. A study found no association between any aspect of wearing a bra and breast cancer risk, and there is little to no plausible biological explanation for how sleeping with a bra would cause the DNA mutations in cells that are necessary for cancer to start.
Having cancer can create major sleep disruptions, affecting the ability to fall asleep and stay asleep through the night.
It is estimated that half of all people with cancer have sleep problems. Some studies have found even higher numbers of sleep disturbances with nearly 70% of women with breast and gynecologic cancers having symptoms of insomnia. The rate of disrupted sleep appears to be even higher in patients with advanced cancer, reaching up to 72%.
Even worse, there are indications that these numbers may be underestimated since many cancer patients do not raise sleep concerns with their doctors.
There are numerous potential causes of sleeping problems in people with cancer:
More than one of these factors may contribute to sleeping problems, which can vary for any individual depending on the type of cancer they have, the treatment they are receiving, and their overall health, including coexisting conditions.
Cancer or cancer treatment may also induce symptoms of other sleep disorders. In a survey of over 1,000 people with cancer, a significant number reported having restless legs, which is the urge to move the legs when lying down. Some types of jaw surgery for cancers of the head and neck can result in obstructive sleep apnea that may need to be addressed with plastic surgery.
For people with cancer who are experiencing sleeping problems, it’s important to talk with a doctor who can discuss their symptoms, what’s causing them, and potential solutions. Because of sleep’s effect on physical health, emotions, and thinking, better sleep can create meaningful quality of life improvements for cancer patients.
Counseling and medications can both benefit sleep. In studies of people with breast cancer, treatment with cognitive behavioral therapy for insomnia (CBT-I), which tries to reframe negative thoughts about sleep, has been found to enhance sleep and mood while strengthening immune function. Combining CBT-I with medications may have additional effectiveness in improving sleep and quality of life.
It may also help cancer patients to upgrade their sleep hygiene, which includes their bedroom setting and daily sleep habits. Examples of these improvements include following a consistent sleep schedule, ensuring the bed and bedroom are comfortable and inviting, and minimizing the use of electronic devices in the lead-up to bedtime.
Being diagnosed with cancer can bring about a variety of significant life changes. The physical and emotional effects of having cancer and going through cancer treatment can be long-lasting, creating diverse challenges for cancer survivors.
In one study of breast cancer survivors who were between six months and five years post-diagnosis, 78% had above-average sleep difficulties. Survivors have also listed sleep as one of the most important issues for their health.
Addressing sleep problems can be especially important for survivors of childhood cancer . Childhood cancer and its treatment often lead to long-term effects, including impacts on both mental and physical development. Quality sleep may help reduce these effects and bolster the immune system to strengthen their overall well-being.
Cancer survivors should talk with their doctor about creating a wellness plan that covers not just sleep but also other important health concerns like diet, exercise, and follow-up care. This plan can include steps for effective sleep hygiene to promote positive sleep habits.
While they may be focused on the well-being of a loved one, caregivers of people with cancer frequently encounter their own sleep challenges. In one study, 89% of caregivers of breast cancer patients reported sleeping problems.
Fragmented sleep from nighttime interruptions to provide care, heightened levels of stress and anxiety, and lack of time to address their own health needs can all play a part in poor sleep among caregivers. Unfortunately, that lack of sleep can create risks for their own health, worsen depression, and hinder their ability to effectively provide quality care.
It’s important for caregivers to make time for self-care, including trying to develop a sleep schedule that is as stable as possible. Other family members, friends, or local organizations may provide services to help with certain aspects of caregiving, enabling a caregiver to find time to devote to their physical and emotional wellness.