Understanding sleep and brain health
How long we sleep and how well we sleep are much-discussed topics in the search for ways to reduce the risk of cognitive decline and dementia. Many of us have experienced temporary impaired memory and thinking following a lack of sleep and research suggests that repeatedly skimping on sleep might have long term effects on the brain. In this article we take a look at the extent to which sleep is connected with cognitive health and what we can do about it.
How does sleep affect the brain and its function?
Cleansing of the brain during sleep
The body carries out some important housekeeping tasks while we are asleep and cleansing of the brain has to be one of the most important ones. Waste products that are an inevitable part of being alive accumulate in the brain during our waking hours and can become potential neurotoxins if they are not removed efficiently. Washing these away via the cerebrospinal fluid is a set of processes known as the glymphatic system.
Importantly, the glymphatic system removes protein plaque substances from the brain that are seen in neurodegenerative conditions such as Alzheimer’s disease. Increased quantities of plaque have been seen in the brain after periods of sleep deprivation. It seems that efficient plaque removal requires not only sufficient sleep but time spent in deep sleep.
This brain-cleansing function of sleep is suggested to be the reason why we spend such a large portion of time in a state – sleep – in which we are vulnerable and otherwise unproductive.
Melatonin: the sleep hormone
Melatonin is the hormone our bodies release in response to darkness so that we can fall asleep. Melatonin has many more benefits, however, than simply making us feel sleepy. It is now known to have strong anti-inflammatory and antioxidant effects, regulating the immune system and helping to protect cells as they age.
Melatonin appears to have specific neuroprotective qualities, helping the regrowth of nerve cells damaged in degenerative brain conditions. It shows promise for inclusion in therapeutic medications for Alzheimer’s and other conditions characterized by degeneration of brain tissue. Melatonin may play a significant role in the ability of good quality sleep to protect and refresh our cognitive function.
Sleep, stress and inflammation
The quality and duration of our sleep impacts other areas of our health, including our reproductive hormones, adrenal (stress) hormones and our immune system. Sleep disorders are known in particular to cause chronic activation of the stress response, leading to disruption in the release of cortisol and other adrenal hormones. This kind of hormonal dysregulation can directly reduce cognitive performance.
Disrupted release of cortisol can lead to further sleep fragmentation, which perpetuates the cycle of abnormal nervous system activation and dampens the restorative function of sleep. To make matters worse, disruptions in the adrenal system appear to contribute to metabolic problems such as high blood pressure and diabetes, as well as to other inflammatory conditions such as cognitive decline and dementia.
Sleep and the brain: a strategy for success
Consider our three-point strategy for better sleep:
1. Morning light
Morning light therapy has been used successfully to help people to align their wake-sleep cycle with the natural circadian rhythm the body is programmed to work best in. Getting in synch in this way supports your body to release melatonin at the right time for falling asleep. It also supports the body to release the right amounts of the stress hormone cortisol at appropriate times of day and night to help us to get up, wind down or stay asleep as required.
Help your body to find its natural circadian rhythm by getting some daylight on your face in the morning: stand outside for a few moments or, better still, go for a walk around the block. In the dark winter months, consider a natural daylight bulb or bedside clock to get you ready for the day.
2. Don’t eat just before bed
When we eat, our blood glucose level naturally rises, triggering the release of both insulin and cortisol. When cortisol levels rise, the release of the sleep hormone, melatonin, is inhibited. Eating just before bedtime can therefore make it harder to fall asleep.
Conversely, leaving a gap of two to three hours between your evening meal and bedtime allows your body to spend longer in a fasted state. This can help the body to regulate its blood glucose and insulin mechanisms, supporting better metabolic and cardiovascular health, both of which are important for the plentiful supply of nutrients and oxygen to the brain.
3. Protect your melatonin production
We have our very own supply of the brain-protective, anti-inflammatory, antioxidant substance, melatonin. We produce it naturally in our pineal gland every evening after darkness falls. However, its production is easily inhibited by exposure to light. We extend our day-time hours with lamps, televisions, laptops and mobile phones whose light signals interfere with the message that night time is approaching. Foster your melatonin production by revamping your evening routine and sleep environment:
- Choose dim, candle-like lamps to signal the arrival of evening.
- Avoid screens or all kinds for the hour before you sleep.
- Choose low-key activities such as meditation, reading or listening to calming music.
- Keep your bedroom free of electronics and standby lights.
- Use curtains or blinds to make your bedroom as dark as possible.
- Use dim nightlights if you have to get up in the night.
- Don’t stress if you don’t sleep well. Research suggests that some better nights of sleep might make up for the bad ones when it comes to cognitive function!
Bredesen, D.E., 2014. Reversal of cognitive decline: a novel therapeutic program. Aging, 6(9), pp.707–17.
Bonaz, B., Sinniger, V. and Pellissier, S., 2017. The vagus nerve in the neuro-immune axis: Implications in the pathology of the gastrointestinal tract. Frontiers in Immunology.
Hauglund, N.L., Pavan, C. and Nedergaard, M., 2020. Cleaning the sleeping brain – the potential restorative function of the glymphatic system. Current Opinion in Physiology, 15, pp.1–6.
Pickel, L. and Sung, H.K., 2020. Feeding Rhythms and the Circadian Regulation of Metabolism. Frontiers in Nutrition, 7, p.39.
Polimeni, G., et al., 2014. Role of melatonin supplementation in neurodegenerative disorders. Frontiers in Bioscience - Landmark, 19(3), pp.429–446.
Xu, W., et al., 2020. Sleep problems and risk of all-cause cognitive decline or dementia: an updated systematic review and meta-analysis. Journal of neurology, neurosurgery, and psychiatry, 91(3).