New Research on Sleep and Immunity 🦠
Hey friends, in honor of Sleep Awareness Week, I thought we would take a look at how sleep affects aspects of immunity.
The connection between sleep and illness has been intuitively obvious to humans for a very long time.
“Sleep and watchfulness, both of them, when immoderate, constitute disease,” said the ancient Greek physician Hippocrates more than 2400 years ago.
However, it's only quite recently, with the advent of technology to objectively measure sleep and the rise of scientific microbiology in the twentieth century, that we've been able to conduct experiments to rigorously test how sleep affects our ability to resist infections.
For instance, Sheldon Cohen at Carnegie Mellon has conducted an array of trials in which brave volunteers are administered nasal drops containing either respiratory viruses or saline (placebo), and then keeping them in quarantine to see if they get sick. In one such study, subjects who were getting less than 7 hours of sleep per night were nearly three times more likely to go on to develop a cold, compared to those who averaged 8 hours.
Furthermore, sleep loss may interfere with the ability of the immune system to respond appropriately to vaccines. When flu vaccines were administered to subjects who were in a state of sleep debt, their mean antibody titers 10 days later were less than half of those in control subjects.
More recently, several studies were published examining how sleep loss affects 1) the odds of developing an infection; 2) antibody response to vaccination; and 3) the probability of experiencing "long COVID" symptoms. We take a look at those below. 👇
This Week’s Research Highlights
Researchers affiliated with the University of Oxford performed a systematic review of studies assessing the association between sleep duration/quality and upper respiratory tract infections. A total of nine observational studies were included in the final meta-analysis. They determined that sleeping less than 7-9 hours was associated with ~31% increased odds of developing upper respiratory tract infections. Sleeping more than 9 hours was non-significantly associated with URTIs. Notably, they did not find a correlation between sleep quality and the risk of infection. However, a new study published a couple of months ago, did find such a relationship. In a study of 1318 military recruits, sleep restriction (drop in usual sleep duration of at least 2 hours per night) more than doubled their odds of developing a respiratory infection…but good subjective sleep quality protected against this elevation in risk.
An international team of researchers performed a systematic review of studies examining how the amount of sleep you get at night is associated with subsequent antibody response. Since previous research has suggested that antibody levels are mostly influenced by sleep in the nights around vaccination, they focused on sleep data that was collected within 7 days of the date that subjects received their shots. Four experimental studies and three prospective cohorts were included in the meta-analysis. When they analyzed studies that relied upon self-reported short sleep (less than 6 hours per night), the researchers did not find a statistically significant relationship to an antibody response. However, when they looked at objectively measured sleep duration (like through a device or a sleep study), they found a robust association between short sleep and reduced antibody response. Why the disparity? Well, it has previously been established that people are really not that great at estimating how long they slept, and they usually err on the side of overestimation — so much so that one model has suggested that people who sleep 5 hours are likely to over-report their sleep duration by 1.2 hours. To try to put the results into a perspective that might be relevant to the current pandemic, the researchers estimated the decline of the immune response to the Pfizer vaccine from baseline based on available clinical data. They calculated that the effect size of short sleep on antibody levels was equivalent to the impact of two months of waning antibody levels commonly seen after a COVID-19 vaccine.
Researchers affiliated with the International Covid Sleep Study Collaboration (ICOSS) conducted a survey to gain insight into how receiving mRNA vaccines influences risk of suffering from long-lasting symptoms of COVID-19, as well as the possible role of sleep in post-COVID symptoms. First, they analyzed data from 9717 respondents on vaccination status and post-COVID symptoms. Post-COVID, here, was defined as experiencing at least one of the core COVID-19 symptoms for at least three months. After adjusting for age, sex, BMI, and other factors, they found that two mRNA vaccinations lowered the risk of suffering from post-COVID by about 21%. Then, the researchers wanted to see how sleep habits might affect this apparent protection. They analyzed data on habitual self-reported nighttime sleep from a subset of 5918 fully-vaccinated participants and split them into three categories based on how much sleep they said that they got. The researchers found that short sleep duration (less than 6 hours per night) was associated with ~59% higher odds of post-COVID symptoms, compared to getting 6-9 hours of sleep nightly. Initially, they also found a similar link between long sleep (more than 9 hours) and post-COVID symptoms. However, when they excluded people whose sleep had only recently been extended to more than 9 hours, the association was abolished. In other words, people who had been getting a ton of sleep since before the pandemic did not have a higher risk of post-COVID. This suggests that the relationship between long sleep and post-COVID symptoms is most likely an example of reverse causality. Basically, people sleep a lot because they are not well, rather than sleeping a lot leading to a greater risk of post-COVID.
Better Brain Fitness with Dr. T
If pleasure is our brain's way of rewarding us for doing things that are good for it, and pain its way of discouraging us from doing things that are bad for it, how is it that it's become commonplace to believe that we must endure discomfort in order for something to be beneficial?
In this issue of The Brainjo Connection, Josh addresses the peculiar phenomenon of the "pain-pleasure inversion," examining when the "no pain no gain" mentality actually applies, and when it's best for us to follow our bliss.
Random Trivia & Weird News
Smallpox is a devastating disease caused by the variola virus. As a result of a tireless vaccine campaign that combed the entire globe, the disease was eradicated in 1980.
The last naturally occurring case of the illness that we know of was diagnosed in 1977. But sadly, this was not the true end of smallpox.
In 1978, a medical photographer named Janet Parker contracted the disease at the University of Birmingham Medical School, where the variola virus was being grown for research purposes.
Henry Bedson, head of the Birmingham Medical School microbiology department at the time, committed suicide shortly after the incident, apparently blaming himself for the tragedy. Very sad story all around.
Videos We Loved This Week
- Anurag Singh: Improving mitochondrial health to treat osteoarthritis with urolithin A. Via Modern Healthspan.
- David Goldfarb: Oxalates and kidney stones. Via Nutrition Made Simple.
Products We Are Enjoying
If you are still adjusting to the switch back to Daylight Saving Time, this could help you out. The amino acid glycine has been shown in some studies to accelerate sleep onset and improve sleep quality. Interestingly, it appears to do this by triggering changes in body temperature. Glycine, in the right dose, increases blood flow to the extremities, which in turn elicits a drop in core body temperature (for a more detailed explanation of how thermoregulation influences sleep, check out this blog). Pretty cool. Studies typically use around three grams, which is why powder is the economical choice here. Fortunately, it happens to taste sweet (hence the name), so it’s pretty easy to add to a drink before bed.