How much sleep do you need to reduce the odds of viral infection?
Updated: Apr 16, 2020
WHO, and governments around the world, have issued public guidance about preventing the spread of coronavirus. Hand washing, social distancing, respiratory hygiene. The UK government has published over 20 pages of detailed guidance for the public, health professionals, businesses and schools - all focused on influencing what happens to virus droplets outside of the body.
We know that it is imperative that we respect this advice.
But, I can't help thinking there’s something missing.
If we’re going to tell people how to use soap and water, is it also worth reminding people what they can do to slow the invasion of covid-19 when it breaches those external defences?
Scientists at the coalface have been a little too busy to run controlled studies to look at how lifestyle choices could help slow the progression of coronavirus as yet, but there’s a pretty significant back catalogue of research to identify the usual suspects for fighting infection: minimising stress, a healthy nutrient rich diet, not smoking, avoiding excess alcohol, regular exercise, exposure to sunlight.. and…(the one that got me up here on the soapbox)... plenty of sleep.
Does more sleep reduce your odds of getting a viral illness?
One the most compelling studies on this was led by Aric Prather, now at UCSF, and building on the work of Sheldon Cohen at Carnegie Mellon University.
164 healthy adults tracked their sleep patterns at home for 7 nights, using a wrist monitor to record how long they slept. They answered a barrage of personal questions. They were then invited to a hotel for 5 nights, where all their meals and a comfortable bed were provided, free of charge. Tempted to volunteer? Well, there was a catch. On day 1 of their 'vacation', they were all given a generous dollop of the common cold virus, applied directly up the nose.
(I can't help thinking it sounds a bit like the Diamond Princess, on a smaller scale.)
Every day, volunteers obligingly donated their nasal mucus, and researchers weighed their tissues. I have nothing but admiration for the participants, and the research team. There was also a blood test, to verify who developed a cold.
Researchers found that 76% became infected with the virus, and 29% had a biologically verified snotty cold.
So, who was most likely to develop a cold?
Yup, you’ve guessed it.
The risk of developing a cold was 4.2 times higher for those who slept for fewer than 6 hours than those who slept for 7 hours or more. The risk was higher still for those who slept fewer than 5 hours (4.5 fold higher risk vs. 7hr+).
Statistically speaking, the link between short sleep and risk of a cold was stronger than all the other characteristics investigated, including age, BMI, education, smoking, alcohol, stress and mood.
So.. could more sleep help to stem the pandemic spread?
All this study tells us is that 7+ hour sleepers seemed to be at lower risk of developing a cold. It doesn’t necessarily follow that if we could persuade all the <6hr sleepers to doze a little longer, there will be less of a queue at the shops for toilet paper. That’s a bit of a leap.
But it’s not the first study to have found connections between sleep and infection risk. For example, in 50,000 women from the Nurses Health Study in the US, both short (<=5hr) and long (>=9hr) sleepers were at higher risk of developing pneumonia.
What’s the link between sleep and immune function?
If you’re into heavy duty science, this detailed open access 50 page review explains plenty of plausible mechanisms for why sleep and immune function are heavily interlinked. I’ll stick to the gist, and a few highlights.
Your immune defences consist of several different varieties of white blood cells - the foot soldiers in the fight against invaders into the body. First the army’s scouts have to recognise foreign bodies, or antigens, and tag them so that the rest of the immune system can spot them. This can be tricky with viruses, since they typically reproduce using the body’s own cells. Invaders are often escorted to the body’s lymph glands so they can be outnumbered. The army destroys the nasties, often using cytotoxins (think James Bond), or eating them alive (think Jurassic Park). Some cells help recognise antigens for a speedy response in the future, i.e. by producing specific antibody, which can multiply rapidly if we see the same infection twice. Crucially, our immune army also has to stay on its toes to avoid causing collateral damage to the body’s own cells.
How does sleep make a difference? Studies in the lab have found that even one night without sleep can interfere with communication between immune cells, making the whole army less efficient, and causing more collateral damage, in the form of inflammation. Inflammation can be part of a healthy response to infection, but too much of it has been linked to chronic diseases, such as heart disease.
Sleep seems to be particularly important for T cell function. T cells help to identify invaders, send out cytokines (messengers) to tell the rest of the army what’s up, and do the dirty work of destruction. We've known for a 20 years that restricting sleep to 4 hours in healthy people can reduce the activity of our ‘natural killer’ T cells by 28%. A study published last year showed staying awake all night interfered with the production of integrins, which help T cells to attach to, and kill, virus infected cells.
Sometimes we use vaccines which are a weak, or imitation form, of a virus. When the vaccine is effective, it’s because the body has ‘learned’ to recognise that particular antigen, and fire up an overwhelming antibody response. Another study from Prather and colleagues found that after a routine Hepatitis B vaccine, >95% of 7+hr sleepers produced a clinically protective response, vs. <75% of those who slept for fewer than 6 hours before they received the vaccine.
We're short on studies which have used better sleep to try and reverse infection risk, but there are a few compelling studies. Michael Irwin from UCLA explored the impact of Cognitive Behavioural Therapy for Insomnia (CBT-I, the number one recommended treatment for insomnia) or Tai Chi in 123 elderly adults, compared with a sleep education control group. There was evidence that CBT-I reduced systemic markers of inflammation, even 16 months later. Tai Chi was also helpful against inflammation, likely due to a reduction in stress - which is ultimately an inflammation driver.
Would it be helpful for governments to include advice about sleep, and self-care?
We know there is a massive international sleep debt. A 2016 study by RAND Corporation found that more than 1 in 3 of UK adults do not routinely get the recommended 7-9 hours sleep each night. With fewer people commuting to work at the moment, perhaps there is an opportunity for some of us to start to address that sleep debt. After all, sleep doesn't involve leaving the house, and it's completely free.
Those at greatest risk will be our over-stretched medical staff, carers, emergency service personnel.. anyone who could be called on 24/7 to help those in need. It is their immune systems that are going to be especially vulnerable to exposure to the virus, and it is they whose sleep is most under threat.
If the government acknowledges the importance of sleep, and other self-care measures to protect your immune system, it could be a valuable reminder to those on the front line, and those who manage their rosters. Beds will be under pressure, patients will be in desperate need, but we must allow medical teams to rest.
Sleep isn’t just for our immune defences. It makes us more human, less stressed, more confident, more rational.
This post is long enough already so I'll jump off the soapbox now, but in summary, if you can protect your sleep, it could help to protect you.