By Benjamin V. Treadwell, Ph.D.

It’s common knowledge that a good night’s sleep is important to our well-being. The complexities of sleep itself, on the other hand, are not so well known.

For example, scientists cannot fully explain the need for sleep at the cellular/biochemical level. However, a recent study (See this month’s “Research Update.”) is opening scientific eyes not only to why we are emotionally and physically drained after a night of interrupted sleep, but also to how chronic insomnia can progress to disease.

The work carried out by the brain during sleep, it turns out, is critical for our emotional health or mood, memory consolidation and the health of the entire body. What does that mean, exactly?

Going deeper

Sleep is not a singular phenomenon; it occurs in several stages. By attaching electrodes to the head during sleep, scientists can identify the electrical waves associated with each stage. More precisely, they can detect and measure the differences in electrical activity associated with the firing of neurons (specific brain cells) and the transmission and propagation of the charge from one neuron to another.

This activity requires an enormous amount of energy. In fact, while in sleep mode, the brain uses the equivalent of one-quarter pound (100-120 grams) of sugar  to produce the energy required for restoration of cellular health and synaptic transmission of nerve impulses.

REM to SWS

When we close our eyes, the initial sleep produces electrical activities associated with eye movement, hence the terminology REM, or rapid eye movement sleep, for the first stage. Subsequent, deeper sleep is referred to as NREM for non-rapid eye movement.

NREM sleep is subcategorized into stages 1, 2, 3, and 4. Stages 3 and 4 are also known as SWS or slow wave sleep. Scientific evidence suggests SWS is perhaps the most important level of sleep, restoring the brain to a healthy, organized state. 

Changing patterns

Our sleep patterns, including the duration of SWS, change as we age. The intensity of this change depends on genetic variations, as well as differences in overall health and lifestyle. For example, a young individual has a considerably longer period of SWS – 60 to 90 minutes - compared to as little as 15 minutes for the average over-60-year-old.

There are also significant differences between slow wave sleep periods for individuals of the same age, again influenced by genetics and/or lifestyle (healthy vs. unhealthy). Those who push themselves and are under constant stress, or whose diet is nutritionally poor, are probably shortening the length of SWS.

From brain to body

In addition to poorer emotional health and memory consolidation, there may be broader health questions associated with shorter slow wave sleep periods. In fact, the recent study mentioned earlier supports a role for adequate SWS in the restoration of whole body function.    

Researchers from the University of Chicago observed that once an individual slipped into SWS, a number of metabolic and hormonal changes occurred. Since these changes involved the regulation of glucose utilization by the brain, the researchers predicted that interrupting SWS would lead to the pre-diabetic state. The fact that type II diabetes and sleep disorders – such as sleep apnea – are often associated, provided further support for the theory.  

Results of SWS interference

The investigators tested their hypothesis on five men and four women. The subjects were wired with electrodes and allowed to sleep for eight hours on three consecutive nights. Each night, the subjects were presented with acoustic tones to prevent them from entering SWS without waking them. In other words, the subjects all slept through the night, but were deprived of their SWS.

Blood samples were drawn periodically to determine glucose levels and glucose tolerance. The results showed a 25% decrease in insulin sensitivity, the capacity of cells to take-up glucose from the blood, compared to baseline levels (glucose sensitivity without SWS interference).  A similar decrease in insulin sensitivity has been recorded in people at high risk for developing type II diabetes.

The results of the University of Chicago study imply that SWS plays an important role in the body as a whole. Just as it is on the neuro-behavioral side, slow wave sleep seems to be critical to physiological hormonal balance (homeostasis).

Changing what we can

Granted, we can’t do much about our genetic constitution. Nor can we reverse the aging process (at least not yet). But there are steps we can take to maintain and/or increase our SWS time:

1. Keep psychological stress to a minimum.

2. Exercise regularly and maintain a healthy weight.

3. Follow a nutritious diet, high in fruits, berries, vegetables and legumes.*

In other words, a healthier lifestyle can help to promote slow wave sleep, which may be the real key to a restoring, good night’s rest.