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  • New research affirms the role sleep plays in supporting immune levels.
  • Sleeping less than six or more than nine hours can increase infection risk.
  • The effects of poor sleep are felt both acutely and long-term.
  • Easy steps can aid in optimizing sleep quality and duration.

Factors such as age, underlying health conditions, and pregnancy are known to increase an individual’s risk of developing infections, such as colds and flu.

However, new research published in the journal Frontiers in Psychiatry has highlighted another element that may influence our risk of getting sick — and we do it daily: sleep.

“The findings are an additional testament to why everyone should prioritize sleep,” stated Ingeborg Forthun, PhD, a researcher at the Norwegian Institute of Public Health and co-author of the study.

Previously, studies have typically focused on sleep and infections in a controlled setting — so the research team wanted to explore their association in ‘real life’ situations.

To obtain insights, they handed out surveys to patients in the waiting rooms of general practitioners in Norway, collecting 1,848 responses overall.

The survey asked questions such as how long they generally slept, when they slept, and whether they considered their sleep to be good quality.

Respondents were also asked to disclose if they’d experienced an infection or taken any antibiotics in the previous three months.

Researchers found that participants who obtained either too little sleep (six hours or less) or too much sleep (nine hours or more) were more likely to develop an infection.

“Those who reported sleeping more than 9 hours were 44% more likely to report an infection compared to those who slept 7-8 hours,” Forthun told Healthline.

On the other hand, she continued, “those who reported sleeping less than 6 hours were 27% more likely to report an infection.”

The data also revealed that those who obtained less than six hours of sleep each night — or had chronic insomnia — were more likely to require antibiotics to tackle their infection.

While sleep duration impacted infection risk, the researchers found no link between this risk and when an individual enjoyed their shut-eye.

“We asked the respondents whether they would characterize themselves as a morning or evening person,” stated Forthun. “But we found no clear differences in risk of infection or antibiotic use by this factor.”

The researchers recognized there is potential for bias in the results, as patient recall about their sleep may be inaccurate.

Furthermore, the scientists did not know why patients were visiting their doctor and if they had a medical concern that may have influenced poor sleep or infection.

However, Forthun said in a statement, they did not believe that these factors “can fully explain our results.”

Scientists have long understood that sleep and our immune system are inextricably linked.

Essentially, “sleep is a time to save and reset the body,” said Dr. Randall Wright,neurologist at Houston Methodist and medical director for Brain Wellness at Houston Methodist The Woodlands Hospital.

“We get to replenish many of the chemicals that our body needs,” he told Healthline. “It is a time for our immune system to bolster itself.”

So how exactly can too little — and too much — shut-eye impact an individual’s immunity levels? There are several factors involved.

“Not getting enough sleep can hinder white blood cells from reaching affected sites in the body,” revealed Dr. Abhinav Singh, medical director at Indiana Sleep Center, an expert at the Sleep Foundation, and co-author of Sleep to Heal: 7 Simple Steps to Better Sleep.

White blood cells are a vital element of our immune system and help the body fight off infections caused by viruses and bacteria.

Lack of sleep can also cause the body to release more of the stress hormones adrenaline and prostaglandin, shared Singh. This is critical, as they “lower levels of integrin, a molecule that helps T-cells (part of white blood cells) stick to virus-infected cells and kill them,” he said.

Poor quality and quantity of sleep can also influence inflammation levels in the body, stated Brittany Morey, PhD, assistant professor of public health at the University of California, Irvine – Program in Public Health.

“During sleep, the body releases certain cytokines, which influence the body’s inflammatory response,” she shared. “When this process is disrupted, the body’s ability to respond to infection is hindered.”

And that’s not all. “Research shows that poor sleep leads to a diminished production of antibodies to fight off infections,” Morey noted.

For instance, in a study of participants given a vaccine for hepatitis B, those who slept six hours or less produced fewer antibodies and were ultimately less protected against the disease.

We’ve covered sleep deprivation, but how does getting too much sleep come into play?

Requiring nine hours or more slumber each night can “often imply that the quality of your sleep is inadequate or that there’s another inflammatory process occurring,” shared Singh.

“Common sleep disorders that increase sleep need include sleep apnea, periodic limb movement disorder, and sleep fragmentation from insomnia, among others.”

These disorders can prevent you from falling into deep restorative sleep, leading to the same effects on the body as getting too little sleep.

Immediate vs. long-term impacts of poor sleep

A poor night’s rest can have both acute and lasting effects on our immunity levels.

“Sleep problems over a long period can have a detrimental effect on one’s immune system and even increase risk for cardiovascular disease and other chronic diseases,” explained Morey.

However, research has revealed that sleep loss over a much shorter duration can also impact immunity.

For instance, one study whereby participants obtained just four hours’ sleep saw their levels of ‘natural killer cells’ significantly reduced. Meanwhile, another study saw participants’ levels of inflammatory cytokines dramatically increase after a single night of poor sleep.

“This is why it’s common for someone to be more prone to getting sick even after one night of bad sleep,” Morey noted.

The good news? Negative impacts aren’t necessarily long-lasting, shared Wright.

“It varies from patient to patient, but we do know that people have shown improvements when they get adequate sleep,” he said. “I do think you will see improvements with healthier sleep patterns and habits.”

For the study participants whose natural killer cells were reduced after a bad night’s sleep, their levels returned to normal after a night of good rest.

Various approaches help improve slumber, and you can start implementing them immediately.

Make sleep a priority

Save that next TV episode or chapter of a book til morning and definitely stop scrolling through social media.

“Recognize sleep as the largest pillar of health, along with nutrition and exercise,” Singh asserted.

Be consistent

“Try to go to sleep at the same time every night and get up at the same time each morning,” recommended Morey. Sticking to a schedule has been linked to more positive health outcomes.

Create a pre-bedtime routine

Singh recommended doing the following for 10-15 minutes each in the hour before bed to help your body (and mind) prepare for slumber: take a warm shower; journal; read a book (not on a screen); practice deep breathing, of 4 breaths in and 8 breaths out.

Optimize your environment

In addition to switching off screens — cell phone, TV, or laptop — at least one hour before bed, make your bedroom sleep-friendly. Ensure the space is “dark, cool (<68°F), and quiet — although white noise is OK,” said Singh.

Exercise regularly

Studies have linked exercise to improved sleep quality and duration. Plus, shared Morey, “exercising can help you fall asleep more easily.”

Seek help if necessary

If you experience a chronic sleep concern, seek help. Your general physician is a good first port of call, while psychologists and psychiatrists may be able to assist with cognitive behavioral therapy (CBT).

The new findings reveal it’s not only sleep quality that can impact infection risk — but also sleep duration.

While too little sleep is often considered detrimental, too much shut-eye can also negatively affect the body.

“Given what we know about how important sleep is for health, we were not surprised by the study findings,” explained Forthun.

That said, she continued, one result was more unexpected: a large number of the surveyed patients (almost half) reported experiencing a chronic sleep disorder.

As such, improving awareness around the link between sleep and infection risk could help those with sleep concerns take steps to enhance their general health.