Sleep 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.

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, metabolism and body weight. Sleep may affect how cells function, altering their environment or the signals that affect how they grow.

How Sleep Affects Cancer Risk

• 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.

• Sleep apnea is believed to generate an environment conducive to cancer.

• 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.

• Researchers have found that long sleep duration, usually defined as sleeping more than nine hours per night, has 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 also been associated with an increase in risk of primary liver cancer and breast cancer, in particular the subtype in which growth is driven by oestrogen.

• In studies with mice, fragmented sleep triggered types of inflammation that promoted tumour growth and progression. A study of over 10,000 adults over the age of 50 found a higher cancer risk in people who rated their sleep quality as intermediate or poor.

• An 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.

• 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.

• 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”.

Sleep and Cancer Progression

Sleep may play a role in how cancer progresses 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.

• 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.

• Obstructive sleep apnea is also believed to have a potential role in cancer progression because hypoxia and sleep fragmentation may enable tumours to more easily metastasise to other parts of the body.

How Cancer Affects Sleep

Cancer survivors list sleep as one of the most important issues for their health.

• 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 gynaecological cancers having symptoms of insomnia.

• The rate of disrupted sleep appears to be even higher in patients with advanced cancer, reaching up to 72%.

• In one study of breast cancer survivors who were between six months and five years post-diagnosis, 78% had above-average sleep difficulties.

There are numerous potential causes of sleeping problems in people with cancer including:

• Pain or discomfort caused by a tumour or by treatment

• Gastrointestinal or urinary problems caused by cancer or its treatment

• Struggles to sleep during hospital stays

• Stress, anxiety, and depression that can result from having cancer

• Infection and fever, which may occur as a result of reduced immune function during chemotherapy

• Cough or difficulty breathing

• Side effects from medications, including pain medications, which may cause drowsiness but interfere with quality sleep

• Disrupted sleep schedule resulting from daytime fatigue and napping

• Symptoms of other sleep disorders induced by cancer or its treatment

Caregivers of people with cancer frequently encounter their own sleep challenges. 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. Lack of sleep can create risks for their own health, worsen depression, and hinder their ability to effectively provide quality care.

• In one study, 89% of caregivers of breast cancer patients reported sleeping problems.

Sources: The Sleep Foundation | Wikipedia | National Library of Medicine