Sleep, immunity share a bidirectional link

Sanders W, et al. Sleep and the immune system. Presented at: APA-AAI Annual Allergy, Asthma & Immunology CME Conference; July 27- 30, 2023; Park City, Utah.

Sanders W, et al. Sleep and the immune system. Presented at: APA-AAI Annual Allergy, Asthma & Immunology CME Conference; July 27- 30, 2023; Park City, Utah.

PARK CITY, Utah — A bidirectional link exists between sleep quality and immune system performance, according to a presentation at the Association of PAs in Allergy, Asthma and Immunology Annual Allergy, Asthma & Immunology CME Conference.

“Most if not all of the conditions that we take care of in an allergy clinic involve the immune system,” William Sanders, DMS, PA-C, owner and physician’s assistant at Allergy Specialty Care, based in Florida, said during his presentation. “We know that a lot of these conditions affect sleep, and we’ve known this for a long time.”

For example, Sanders said, patients with rhinitis breathe through their mouths and do not sleep well. Patients with asthma wake up coughing and short of breath, he continued, and patients with atopic dermatitis and urticaria do not sleep well either.

“But the question I’ll ask you today is, does it go the other way?” Sanders said. “As a matter of fact, it does.”

When anything causes stress to the immune system, inflammatory molecules such as cytokines and prostaglandins promote sleepiness, Sanders said. This sleep stimulates the release of melatonin, which activates the innate and adaptive immune systems.

This further triggers an inflammatory response that increases sleep duration and intensity but also may disrupt sleep, Sanders said.

“The take-home message here is that the enhancement of sleep during infection feeds back the immune system to promote host defense, which is associated with reduced infection risk,” Sanders said. “It can improve infectious outcomes and improve vaccination responses.”

Sanders cited a 2015 study of 164 healthy adults who were exposed to a dose of live culture in their nose and then had their sleep measured for a week. Those who slept fewer than 5 hours a night had an almost 50% infection rate, but those who slept 7 hours or more had an 18% infection rate.

“After many nights of reduced sleep, the body becomes immunologically weak,” Sanders said.

A 2002 study, Sanders continued, involved healthy adults who were divided into a group that got 4 hours of sleep a night and a group that got between 7.5 and 8 hours of sleep a night, both for 6 nights, before getting a standard influenza vaccine.

The participants with a full night’s sleep had a robust antibody response to the vaccine, whereas those with diminished sleep had less than half the antibody response of their peers.

“Even after they let them sleep for 2 to 3 weeks after to recover their antibody response, they just still didn’t get it,” Sanders said. “Here again, this suggests that the response to the flu shot is impaired in those with chronic sleep deprivation.”

Just as sleep supports memory formation in the brain, Sanders said, it also supports memory formation in the immune system.

“In order for you to remember something in the brain, you have to sense it,” Sanders said.

Memory comprises three processes, Sanders said: encoding, which is the uptake of information; consolidation, which transfers information to long-term storage during sleep; and recall, which is retrieval of stored memory.

Similarly, during the encoding phase, antigen-presenting cells (APCs) uptake pathogens. APCs then transfer information, or the antigen, to T cells during the consolidation phase. Activation of T and B cells represents recall.

“That happens in the innate immune system,” Sanders said.

As part of the immune system, Sanders said, natural killer cells target malignant tumor cells.

“They’re kind of like the Navy SEALs, or the Rangers of the immune system,” Sanders said.

In a 1994 study, after 1 night of just 4 hours of sleep, 23 medically and psychiatrically healthy male volunteers experienced a greater than 70% reduction in their natural killer cell activity.

“If that’s 1 night, maybe that isn’t such a big deal,” Sanders said. “If it’s weeks, months, years, that could be devastating.”

Sleep deprivation impacts tumor-associated macrophages as well, Sanders said. M1 cells, which are pro-inflammatory, cytotoxic and antitumorigenic, are diminished with sleep deprivation. But M2 cells, which are immunosuppressive and pro-tumorigenic, increase with sleep deprivation.

Multiple studies have shown that nighttime shift work and disrupted circadian rhythms increase the risk for breast, prostate, uterus and colon cancers, Sanders said, adding that Denmark was the first country to pay worker’s compensation to women when they develop breast cancer after years of night shifts in government jobs.

In fact, Sanders said, the International Agency for Research on Cancer has labeled nightshift work a probable carcinogen.

“The lack of sleep ramps up the sympathetic nervous system,” Sanders said. “It provokes a sustained inflammatory response, and this chronic inflammation provides a favorable environment for cancer growth and metastases.”

Adults should get an average of 7 hours to 9 hours of sleep a night, Sanders said, with multiple strategies for achieving that total.

“First of all, all the experts feel you should stick to a sleep schedule,” he said. “Make sure you go to sleep about the same time every night.”

Exercise is helpful as well, he continued, although it should be avoided later in the day. Caffeine should be avoided later in the day as well, he said.

“Caffeine has a 5- to 6-hour half-life. That means it’s got a quarter life of 12 hours or so,” Sanders said. “You don’t want to drink coffee too late in the day.”

Sanders also advises people to avoid alcoholic drinks before bed.

“A lot of us like to have a nightcap. The research shows it can really mess up your sleep. [For instance, you may have] micro-wakeups, [when] you may not even know you’re waking up, but you wake up in the night. And it also affects your REM sleep,” he said.

Large meals and beverages late at night could lead to reflux and other complications that keep people up, Sanders said, while medications with stimulants can also have the same effect. Naps also should be avoided after 3 p.m..

For a good night’s sleep, Sanders encourages relaxation before bedtime. Hot baths and saunas, for example, stimulate vasodilation.

“And then, ideally, you really want to put your money into your bedroom,” he said. “Really make your bedroom conducive to sleep.”

Bedrooms should be dark and cool, he said. They also should be free of gadgets such as phones and tablets, because the blue light from screens shut down melatonin production.

During the day, people should strive to get at least 30 minutes of sunlight, which helps set internal body clocks.

“Finally, you don’t want to lie awake in bed. If you’re lying in bed for a long time, you probably want to get up and do something,” Sanders said. “You wouldn’t want to just sit down at the dinner table and wait until you get hungry.”

Noting that there is a bidirectional link between sleep and immunity, Sanders concluded that sleep deprivation impairs immunologic function and memory. It also increases risks for infectious diseases and cancer, he said.

“Sleep deprivation affects essentially every system of the body,” he said. “You want to implement habits for good sleep.”