Health effects of sleep deprivation

“Sleep helps us get rid of harmful substances in the brain that, in the long run, can cause us to develop Alzheimer’s. Brain cells change a bit, for instance, when we’re asleep: the spaces between them get bigger, improving the flow that removes harmful substances,” Cedernaes says.

Nevertheless, a poor night’s sleep is no reason to panic, he says soothingly. But how worried should parents of small children, for example, be about their constantly disrupted night-time rest?

“We’re keen to study the parenting years because, on average, a significant proportion of sleep is lost. According to the data we sleep researchers have, recovery appears possible if we get time for recuperation. And over time, the risk is reduced. Uppsala researchers have seen this effect, among others, in employees who have worked shifts for many years. Shift workers are a group known to have a higher risk of dementia, probably because they often get too little sleep and at the wrong time in the 24-hour cycle.”

When Cedernaes studies human subjects, they are invited to spend a few nights in a sleep lab where researchers can keep a close eye on them.

“We’re aiming to do clinical studies where we can isolate the impact of individual factors. We do this by controlling how much and what they eat, telling them how much to move and controlling their light exposure. We take blood samples in the morning and evening, and tissue samples too. I’ve specifically focused on sampling muscle and fat, since these tissues are so important for our metabolism.”

Participants’ metabolism, brain function and nerve-cell health are tested. The subjects are encouraged to go to bed at their usual time to maintain their natural circadian rhythm. If the scientists are looking at how sleep deprivation affects health, the participants are kept awake for a certain period or all night.

One aspect Cedernaes finds particularly intriguing is how sleep affects metabolism. While we sleep, the body saves energy and metabolism slows down. In people who are awake at night, a change in behaviour is seen that raises their risk of gaining weight.

“If you don’t sleep enough, your brain gets signals that you aren’t getting enough energy, which boosts the urge to eat sweet foods. When we let sleep-deprived participants eat what they want, they tend to go for more confectionery.”

But in those who are awake at night, changes also occur at genetic and molecular level. These affect how energy is metabolised and stored in the body. During a natural circadian rhythm, the muscles are programmed to burn fat at night and carbohydrates during the day, while adipose tissue (body fat) stores fat by day and releases it at night. If we eat at the wrong times, the system is disrupted, and poor sleep over a long period increases the risk of insulin resistance and, eventually, diabetes.

“We can see changes in how the so-called ‘clock genes’ are regulated. They’re a few genes that control our circadian rhythm. In mice, my colleagues and I managed to show that if you remove these genes in the brain, the animals eat at the wrong time of day and get diabetes. These genes are an important part of the brain: located in the hypothalamus, they regulate the body’s metabolism and satiety signals.”

People with poor sleeping habits are not only at risk of “lifestyle diseases”, but also more susceptible to infections. Cedernaes is eager to explore this more closely. During the pandemic, he and colleagues abroad therefore looked at whether sleep can protect against COVID-19, and found some support for this hypothesis.

Cedernaes constantly has new studies under way, and is currently investigating how and whether physical activity can mitigate the health risks of sleep deprivation.

“I’ve long been interested in exercise and nutrition, and what happens to the body when we exercise and eat certain foods. As a rule, my own sleeping habits are good, but I often subject myself to sleep deprivation to carry out my studies and when I fly through different time zones. My experience is that doing this helps me get new research ideas at the same time.”

Cedernaes’ curiosity about the effects of sleep was aroused when he was very young. His grandfather Lennart Wetterberg was a professor of psychiatry, a member of the Nobel Assembly for Physiology or Medicine, and spent a considerable amount of time studying sleep in both Sweden and the US.

“He made important discoveries about melatonin, the sleep hormone. I’ve always been interested in hearing and seeing what he’s researching. Now in his 90s, he’s extremely clever and has even got involved in COVID. He’s tremendously inspiring.”

Cedernaes’ own academic career began with medical studies at Uppsala University. While working on his PhD thesis in nutritional physiology, he had the opportunity to help with sleep studies. He was fascinated by the fact that the impact of sleep on our health is measurable right down to cellular level.

After completing his thesis, he went to the US. Today, he still collaborates with Northwestern University in Chicago, mainly on studies of sleep and circadian rhythms in mouse models.

“Studying sleep is rewarding. It’s an interesting research area where much remains unknown. I hope to find biomarkers for the people most at risk of being harmed by shift work, for example – and see if such risks can be minimised through, for example, exercise or a particular diet. Many health conditions are linked with disrupted sleep, so there’s a lot of scope for improved diagnostics.”