THE AWESOME POWER OF SLEEP
BBC Focus - Science & Technology|May 2021
Matthew is a professor of neuroscience and psychology and the director of the Center for Human Sleep Science at the University of California, Berkeley. He is also the author of the international bestseller, Why WeSleep: The New Science Of SleepAnd Dreams, published by (£10.99, Penguin Random House).
DR MATTHEW WALKER
Our 24/7 society seems to be slowly robbing us of our slumber, but at what cost?

Sleep is the single most effective thing we do each day to reset the health of our brain and body. It’s an extraordinary elixir that can help you age well and live longer. Here’s what we know about Mother Nature’s cure-all...

WHAT HAPPENS IF YOU HAVE TOO LITTLE SLEEP?

Short sleep is associated with an increased chance of having high blood pressure, a heart attack, and/or a stroke. Even the loss of a single hour of sleep can be heartbreaking, quite literally. There is a global experiment conducted on over 1.5 billion people across 70 countries twice a year. You know of this experiment. It is called Daylight Saving Time. According to a study published in 2014 in the journal Open Heart that looked at more than 42,000 hospital admissions for heart attacks, in the spring, when we lose an hour of sleep, there is a 24 per cent increase in heart attacks the next day.

Even your hormones take a turn for the worse when sleep is lost. Young healthy men sleeping just four hours a night for four nights end up with a level of testosterone equivalent to that of someone 10 years older, according to a small study published in the journal JAMA in 2011. In other words, inadequate sleep, even for a few nights, will ‘age’ a man by over a decade in terms of such hormonal virility. We see equivalent impairments in female reproductive health and hormonal profiles due to a lack of sleep.

There’s also an intimate relationship between your sleep health and your immune health. People who are getting less than seven hours of sleep a night are nearly three times more likely to become infected by a rhinovirus, or common cold. If you are not getting sufficient sleep in the week before getting your annual flu shot, you may produce less than 50 per cent of the required antibody response, rendering the vaccination far less effective. We and others are actively studying whether similar relationships hold for COVID-19.

A lack of sleep significantly increases anxiety, and is associated with higher rates of depression. Recently, studies have shown that insufficient sleep markedly increases the chance of suicidal thoughts, suicide planning, and tragically, suicide completion. In contrast, proper sleep will gift quite remarkable health benefits in myriad ways, nurturing our memory and learning, and boosting our immunity, physical fitness and mental health.

Strangely, one upside of the pandemic situation that many (though not all) people have experienced is greater freedom with their sleep schedule. When we had to commute and get kids to school, we were forced onto an early schedule. For the larks among us – what we call ‘morning chronotypes’ – that was fine. But for the night owls, or ‘evening chronotypes’, this was brutal. And it is not your choice which of these you are. It is largely genetic. It is not your fault, and it is imprinted during conception. With greater bedtime freedom, we essentially saw a ‘revenge of the night owls’, as they started to sleep in harmony with their natural, 24-hour biological rhythm. I only hope this freedom remains as we begin to make our way out of the pandemic.

HOW MUCH SLEEP DO WE NEED?

Based on the weight of tens of thousands of scientific studies, most adults should strive for somewhere between seven to nine hours of sleep each night. Indeed, respected health institutions, such as the Center for Disease Control (CDC), now stipulate a minimum of seven hours of sleep for the average adult.

Based on the wealth of evidential knowledge, such reasoning is sound. For example, consistently sleeping less than six hours is linked to numerous health conditions including certain forms of cancer, Alzheimer’s disease, diabetes, being overweight or suffering from obesity.

CAN SLEEP KEEP YOUR BRAIN HEALTHY?

Insufficient sleep is fast becoming one of the most significant lifestyle factors that may influence whether you go on to develop the form of dementia we call Alzheimer’s disease. It is an area of research my team and I have been fortunate to do a lot of work in. For some years, we knew that people sleeping six hours or less each night, as well as those with sleep disorders such as insomnia and sleep apnoea, had a significantly higher likelihood of developing Alzheimer’s disease.

In patients we see with Alzheimer’s disease, there is a sticky, toxic protein that has accumulated within their brains, called beta-amyloid. Alongside another toxic protein, called tau, it is a key component of the Alzheimer’s disease cascade. Now we know that a lack of sleep is a causal factor resulting in a greater accumulation of beta-amyloid in the brain, setting up a pathway to Alzheimer’s disease. Yet the breakthrough came when Prof Maiken Nedergaard, a neurologist at the University ofUniversityof Rochester in New York, revealed a stunning revelation in mice. She discovered a ‘sewage system’ in the brain that we never knew existed, called the glymphatic system (much like the lymphatic system in your body).

The brain’s glymphatic system helps remove all of the dangerous metabolic contaminants and detritus that build up in the brain as we are awake, including and critically, beta-amyloid. However, this cleansing system only kicked into high-flow gear when the mice were in deep sleep. And if you prevent a mouse from getting that essential deep sleep, there was an immediate increase in beta-amyloid deposits in the brain.

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