William RevilleProf. William Reville examines the reasons why sleep is so important
Despite the fact that we spend about one third of our lives asleep, science still has much to learn about what happens in the sleeping brain and how this activity helps us. Research (summarised by Alice Park www.time.com 11/09/2014) is now uncovering the details of biochemical activity in the sleeping brain and explaining why this activity is essential to the maintenance of our mental faculties.
The principal cell type in the brain is the neuron or the nerve cell. The neurons carry the electrical signals that allow us to think, to register sensations, to store memories and so on. A single human brain contains 86 billion neurons. The other main type of cell in the brain is the glial cell. The glial cells support the neurons, but do not carry electrical signals themselves.
Recent research by Dr Maiken Nedergaard and others at the University of Rochester shows that glial cells play an important housekeeping role in the sleeping brain.
You might think that when yougo to sleep, your brain simply turns off, but this is far from the truth. The brain continues working, but in a different way to the waking brain.
Hormones checked
The electrical activity of the neurons flows more synchronously through the sleeping brain than through the waking brain. During the day, the waking brain is flooded with too much information to all be processed in real-time. Data processors in the sleeping brain sort out this unprocessed information.
The sleeping brain also checks its hormone, proteins and enzyme levels and resets these levels within tolerance as necessary. Finally, and most importantly, a ‘cleaning crew’ in the sleeping brain removes all the toxic rubbish that has built up during the waking day.
These various activities in the sleeping brain are essential to restore and rejuvenate both the brain and the body after a hard-working day. It is important that we get the recommended amount of sleep in order to ensure adequate mental concentration and memory recall when awake.
Getting the recommended amount of sleep also helps to control body weight by encouraging our natural fat burning mechanisms, to resist the development of type 2 diabetes and to battle anxiety and depression.
How much sleep do we need? The US National Sleep Foundation recommends the following hours of sleep per day for the various ages: 10-13 hours (3-5 years); 9-11 hours (6-13 years); 8-10 hours (14-17 years); 7-9 hours (18-64 years); 7-8 hours (65+ years).
American studies show that insufficient sleep is a public health epidemic – almost 40% of adults drop off into an unintentional doze at least one day per month, some while driving.
One of the most important tasks carried out by the sleeping brain is waste disposal. The human body is composed of cells and all cells burn food to release energy to power their various activities. The brain is a voracious consumer of energy. Generating and burning energy inevitably produces by-products that can injure the cell, some immediately and others, if allowed to accumulate, will clog up and damage the cell.
The situation is something like burning coal in an open grate. The burning process generates an inevitable residue of useless cinders and ash that must be removed regularly or they will quickly clog up the grate and prevent the setting of further fires.
In the sleeping brain, the glial cells slow down the electrical activity of the neurons by about two thirds. Neurons make up about 86% of the volume of the waking brain but neuron volume shrinks by about 15% in the sleeping brain.
This allows the fluid that bathes the cells to slosh about more vigorously in the sleeping than in the waking brain and to more efficiently carry away the waste products that have accumulated during the waking day.
One potent class of damaging by-products that arise in living cells from producing and using energy are called free radicals. These free radicals must be efficiently neutralised. Chemicals called anti-oxidants are naturally produced in the cell and have the capacity to mop-up free radicals. The sleeping brain produces copious amounts of antioxidants. But, if you’re not getting sufficient sleep you will not produce enough antioxidants to deal adequately with the free radicals, allowing them to build up and to kill some neurons (recent research by Professor Sigrid Veasey and others at the University of Pennsylvania).
Dead neurons are not replaced. When we don’t get enough sleep, we don’t give the sleeping brain sufficient time to dispose of its garbage. This will prematurely age the brain and may accelerate the appearance of certain degenerative diseases characteristic of later life.
As we age, our brains naturally become less efficient at disposing of its own garbage and the quality of brain function declines. Older brains are more prone to develop Alzheimer’s disease, a form of dementia that destroys memory and the ability to plan ahead.
Alzheimer’s disease is caused by a build-up of amyloid protein in the brain because it isn’t being cleared away quickly enough.
Eventually, the buildup interferes with nearby healthy neurons and symptoms of dementia appear.
So, what do you do if for some reason you lie awake for most of the night, getting only one hour’s sleep? Well, recent research published online in The Journal of Clinical Endocrinology and Metabolism (10/02/2015) has shown that at least some of the negative effects of your restless night can be compensated for by napping the following day.
Eleven men supplied urine and saliva samples after sleeping only two hours the previous night. Analysis showed a 2.5 fold increase in levels of the hormone norepinephrine, which responds to stress, and low levels of the protein interleukin 6, which is important for a healthy immune system.
The increased norepinephrine raises heart rate and blood pressure, but when the men were allowed to take two 30-minute naps the day following the sleepless night, no changes were measured in their hormone or protein levels.
However, napping or catching up on lost week-day sleep on the weekends, while useful, is not the solution. It will help a little but will only partially compensate for the loss of natural sleep.
Trying to compensate for inadequate sleep by napping is like trying to compensate for eating junk food at your main meals by eating healthy snacks mid-morning and mid-afternoon.
William Reville is an Emeritus Professor of Biochemistry at UCC tttp:understandingscience.ucc.ie