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Poor Sleep Weakens Immunity Against Diseases Such as COVID-19

“We have a lot of evidence that if you have an adequate amount of sleep, you definitely can help to prevent or fight any kind of infection,” said Monika Haack, a psychoneuroimmunologist at Harvard Medical School, to National Geographic.

Whether it be protection from the common cold or enhanced immunity to more serious illnesses, the importance of sleep in maintaining health is widely recognized. Haack stresses the importance of sleep as a kind of preventative mechanism, suggesting that perhaps deaths could be prevented and the severity of symptoms could be decreased. “I think that needs more research,” she said. Indeed, numerous studies have shown that less than five or six hours of sleep or subpar sleep efficiency is associated with higher rates of respiratory infections, including head colds, influenza, and pneumonia. 

“The prevalence of sleep problems during the [Coronavirus Disease 2019] COVID-19 pandemic is high and affects approximately 40% of people from the general and health care populations,” according to a Feb. 2021 meta-analysis conducted by researchers in Bahrain, Saudi Arabia, Canada, the United Arab Emirates, and the United States.

The study examined 44 papers involving 54,231 participants from 13 countries. Patients actively suffering from COVID-19 were found to have the highest prevalence rates of sleep problems, with a pooled rate of 74.8%. Longitudinal studies are needed to determine if sleep problems continue long-term, but these findings highlight the importance of researching and prioritizing sleep during the pandemic.

Susceptibility to colds

A clear link between short sleep duration and illness was suggested by a 2015 study conducted by researchers at the University of California, San Francisco (UCSF), and Carnegie Mellon University in Pittsburgh. A total of 164 healthy adults volunteered to wear sleep-tracking devices on their wrists and keep sleep diaries for seven consecutive days. There were subsequently given nasal drops of rhinovirus, a possible cause of the common cold, and quarantined for five days.

Sleep data showed that the odds of developing a cold were more than 4 to 1 in subjects who slept less than six hours compared to those who slept more than seven hours per night. One of the study’s authors, Aric Prather, a psychoneuroimmunologist at UCSF, told National Geographic that the immune responses to both rhinovirus and coronavirus appear similar is a logical assumption given that the two viruses cause the majority of common colds.

According to a 2015 study, subjects who slept less than six hours were more likely to display the common cold’s clinical symptoms, such as sneezing. (Image: tinafranklindg via Flickr CC BY 2.0)

Circadian rhythm disruptions

The COVID-19 pandemic has radically changed millions of people’s routines concerning sleep schedules and the amount of exposure to sunlight. When sleep does not occur at regular times each day or for optimal lengths of time, consequences tend to arise.

An individual’s circadian rhythm, or internal regulator of physiological and behavioral activities within 24-hour cycles, can be disturbed such that daily occurrences like sleep and wake times are dysregulated. Environmental, hormonal, and lifestyle factors disrupting the circadian rhythm can lead to an increased incidence of mental diseases such as depression and physiological ailments such as cancer, cardiovascular disease, and diabetes.

Too much sleep can also be harmful, as evidenced by a 2020 study from Korea published in Nature. Sun exposure plays a critical role in maintaining a regular circadian rhythm and promoting the production and activation of a form of vitamin D called 25-hydroxyvitamin-D [25(OH)D]. The authors investigated the complex relationship between sleep, sun exposure, and vitamin D status by analyzing nationwide surveys between 2010 and 2012 of 14,490 participants between the ages of 19 to 97.

After adjusting for factors that could bias the results, such as demographic data, physical characteristics, lifestyle status, and socio-demographic variables, the researchers found that those with low sun exposure and excessive sleep (over 10 hours) had relatively low levels of circulating 25(OH)D.

Strengthening immunity

Vitamin D and its metabolites, including 25(OH)D, are actively involved in natural immune responses. Vitamin D deficiency has been associated with pathologic conditions such as infections, autoimmune diseases, and allergic diseases. The Korean researchers’ final recommendation was for those who had limited sunlight exposure to maintain adequate vitamin D status, which could help facilitate more appropriate sleep durations.

A gentleman works at home, a common theme during the COVID-19 pandemic. Limited sun exposure and disruption of the circadian rhythm are associated with suboptimal sleep. (Image: Marc Samsom via Flickr CC BY 2.0)

Immunological maintenance and response

Optimal sleep promotes well-being and mental health and has plentiful immunological and health benefits. Researchers in Brazil published an article in Sep. 2020 explaining how sleep affects innate and adaptive immunity. Innate immunity is the body’s first defense line, including skin, mucous membranes, and immune cells such as natural killer (NK) cells. In contrast, adaptive immunity is acquired and involves the proliferation of T and B lymphocytes and antibody production.

Communication within and between the innate and adaptive immune systems is facilitated mainly by signal proteins called cytokines. Interleukin-1β (IL-1β), IL-6, and Tumor Necrosis Factor-Alpha (TNF-α) are examples of pro-inflammatory cytokines involved in inflammatory and immune responses. 

While inflammation is a natural mechanism that protects the body from infection and disease, too much inflammation can damage healthy tissues and organs. In a 2017 study of 60 females with cancer, cardiovascular disease,, poor sleep quality was associated with higher pro-inflammatory cytokines, including IL-1β, IL-6, and TNF-α.

Other studies have shown that participants who continually get less than six hours of sleep have decreased T lymphocytes, decreased NK cell activity, shorter lengths of telomeres of white blood cells, and increased inflammatory markers such as C-reactive protein and IL-6. In other words, poor sleep quality and less than six hours of sleep are associated with unfavorable changes in levels and activity of immune cells.

How do I improve my sleep?

In ancient times, Taoist practitioners strove to maintain health during the day and maximize the quality of sleep through various sleep regimens. In addition to optimal sleep positions, individuals can work on setting a regular sleep and wake schedule to minimize disruptions to their circadian rhythm. The addition of aerobic exercise will not only help to strengthen immunity and decrease the risk of chronic diseases but will also increase the proportion of restorative sleep.

Spending time outside to get sunlight exposure will help to reset one’s biological clock and increase levels of vitamin D. Furthermore, there are countless sleep hygiene strategies that will help to ensure restful sleep, such as limiting caffeine intake during the afternoon and evening, restricting in-bed activity to predominantly sleep only, and establishing a night routine to achieve a tranquil state before bed.

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  • Steven Li is a medical professional with a passion for lifelong learning and spreading positivity and truth to the world. He has a Doctor of Medicine (MD) degree and additional graduate degrees in physiology and business. His zeal for business and marketing has been cultivated through healthcare and technology-related consulting projects. He also has a love for music and the performing arts.

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