Most of us have trouble thinking properly after a bad night’s sleep – we feel foggy and don’t perform at our usual level at school, university or work. You may notice that you can’t concentrate very well, or that your memory seems to be out of order. However, decades of poor sleep can potentially lead to cognitive decline.
Poor sleep also affects the mood and behavior of people, whether they are young babies or older adults. So how much sleep does our brain need to function properly in the long run? Our new research study, published in Nature Aging, provides an answer.
Sleep is an important part of maintaining normal brain function. The brain reorganizes and recharges itself during sleep. In addition to removing toxic waste byproducts and boosting our immune system, sleep is also key to “memory consolidation,” transferring new segments of memory based on our experiences into long-term memory.
An optimal amount and quality of sleep allows us to have more energy and better well-being. It also allows us to develop our creativity and thinking.
When looking at babies aged three to 12 months, researchers have noted that better sleep is associated with better behavioral outcomes in the first year of life, such as being able to adapt to new situations or regulating emotions efficiently.
These are important early building blocks for cognition, including “cognitive flexibility” (our ability to easily change perspectives), and are linked to well-being later in life.
Sleep regularity appears to be related to the brain’s “default mode network” (DMN), which involves regions that are active when we are awake, but not engaged in a specific task, such as resting while our minds wander. This network includes areas important for cognitive function, such as the posterior cingulate cortex (which deactivates during cognitive tasks), parietal lobes (which process sensory information), and the frontal cortex (involved in planning and complex cognition).
There are signs that poor sleep in adolescents and young adults may be associated with changes in connectivity within this network. This is important because our brains are still developing into late adolescence and early young adulthood.
Disruption in this network can therefore have knock-on effects on cognition, such as interference with concentration and memory-based processing, as well as more sophisticated cognitive processing.
Changes in sleep patterns, including difficulty falling asleep and staying asleep, are important hallmarks of the aging process. These sleep disorders are highly plausible candidate contributors to cognitive decline and psychiatric disorders in the elderly.
Getting the right amount
Our study aimed to better understand the link between sleep, cognition, and well-being. We found that both insufficient and excessive sleep contributed to impaired cognitive performance in a middle-to-old population of nearly 500,000 adults from the UK BioBank. However, we have not studied children and adolescents, and as their brains are developing, they may have different needs for optimal sleep duration.
Our main finding was that seven hours of sleep per night was optimal, with more or less than that conferring fewer benefits for cognition and mental health. In fact, we found that people who slept that much – on average, performed better on cognitive tests (including processing speed, visual attention and memory) than those who slept less or more. Individuals also need a steady seven hours of sleep, without too much fluctuation in duration.
That said, we all react slightly differently to lack of sleep. We found that the relationship between sleep duration, cognition and mental health was mediated by genetics and brain structure. We noted that the brain areas most affected by sleep deprivation are the hippocampus, known for its role in learning and memory, and areas of the frontal cortex, which are involved in the top-down control of emotions.
But while sleep can affect our brains, it can also work the other way around. Age-related shrinkage of brain regions involved in sleep regulation and wakefulness may contribute to sleep problems later in life. For example, it may decrease the production and secretion of melatonin, a hormone that helps control the sleep cycle, in older adults. This finding seems to support other evidence suggesting a link between sleep duration and the risk of developing Alzheimer’s disease and dementia.
While seven hours of sleep is optimal for protection against dementia, our research suggests that adequate sleep may also help alleviate dementia symptoms by protecting memory. This highlights the importance of monitoring sleep duration in elderly patients with psychiatric disorders and dementia to improve their cognitive functioning, mental health and well-being.
So what can we do to improve our sleep for optimal cognition and well-being in our daily lives?
A good place to start is making sure the temperature and ventilation in your bedroom is good – it should be cool and airy. You should also avoid too much alcohol and watch thrillers or other exciting content before going to bed. Ideally, you should be in a calm and relaxed state when trying to fall asleep. Thinking about something fun and relaxing, like the last time you were at the beach, works for a lot of people.
Technological solutions such as apps or wearable devices can also be beneficial for mental health, sleep tracking and ensuring consistent sleep duration.
Therefore, in order to enjoy life and function optimally in everyday life, you may want to monitor your own sleep patterns to make sure you get seven hours of sleep on a regular basis.