Why we need sleep and how it affects our health

Our ancient ancestors viewed sleep as a mysterious, inert state that somehow played a role in survival. For them, sleep also made practical sense as a way to recuperate from fatigue and avoid night-time dangers like being eaten by predators or falling off cliffs. Researchers are just beginning to fully understand the complexities of our sleeping selves and its powerful impact on our waking lives.

Why we sleep

We sleep for two reasons: First, our bodies run in cycles called circadian rhythms, of which the sleep cycle is one. Many of these cycles, such as heartbeat, blood pressure, respiration, metabolism and temperature, drop or slow down during the sleep cycle.

Mission control for all these processes is a part of the midbrain called the suprachiasmatic nucleus. This is where your master body clock is located. If this nucleus is damaged or removed, you end up taking lots of short naps instead of one long sleep period.

Your circadian rhythms are set by various time cues called zeitgebers. Light is the most powerful zeitgeber that affects sleep. Daylight wakes you up and darkness triggers the release of the hormone melatonin that brings on sleep. Noise and temperature also play key roles in the regulation of your sleep schedule.

The second reason we sleep is because the longer we’re awake, the greater our need for mental and physical restoration. It takes one hour of sleep to pay for every two hours of wakefulness. So we start to tire after being up for about 16 hours. Sleep debt is cumulative, which means the longer you deprive yourself of rest, the more you’ll need it to feel rested. How drowsy or alert you are depends on both your circadian rhythms and your sleep debt.

While you are sleeping…

Given that we spend [or should] spend one-third of our lives sleeping, it’s alarming how little we know about our down time. Does it surprise you that 40 per cent of laypersons and physicians think the brain shuts down and takes rest when we fall asleep?

Many people believe that soon after going to bed they drift into deep sleep, remain there for some time, have an occasional dream, and then awaken for the new day. Actually, there are several stages of sleep, each marked by significant physiological changes.

The night is divided into non-REM [non-rapid eye movement] and REM [rapid eye movement] sleep. REM sleep is the period in which most dreams take place. Non-REM is also referred to as ‘slow-wave’ sleep and is subdivided into several stages, earmarked by different brainwaves and purposes.

Non-REM sleep

As you close your eyes, your brainwaves become slower and more regular. This stage is akin to meditation. Next is the Stage 1 period, which lasts for about five minutes as your breathing slows and your large muscles begin to relax.

The transition to Stage 2 is sometimes marked by a fleeting sensation of falling, causing you to wake momentarily with a jerk [not referring to your spouse]. During this period, you disengage from the environment and become blissfully unaware of any outside stimuli. Researchers believe Stage 2 is the beginning of actual sleep. It’s marked by spikes in brainwave activity called sleep spindles and K-complexes, which interrupt those previously regular waves.

Stage 2 lasts 10 – 25 minutes, but you’ll return to it several times before daybreak, accounting for half of your night’s slumber.

Next comes Stage 3 sleep, which is characterised by slow brainwaves called theta waves. These are interspersed by even slower delta waves. You’ll spend just a half-hour here, but eventually it will comprise up to 20 per cent of your total night’s sleep.

When the theta waves disappear, you enter stage 4. This is the deepest sleep stage, which consists totally of delta waves. On your initial visit it lasts for 30 – 40 minutes. If aroused during Stage 4, you’ll feel groggy and disoriented. During this stage, blood pressure drops, respiration slows and blood flow to your muscles decreases.

The secretion of growth hormone by the pituitary gland also peaks, stimulating body development and tissue repair. That’s why uninterrupted deep sleep of significant duration is especially critical for children and adolescents. And it’s also why we sleep more when we’re sick. So in Stage 4, you’re completely unaware of your surroundings and at your most vulnerable. It’s the closest humans get to hibernation.

REM sleep

After 30 – 40 minutes of Stage 4 sleep, you re-trace your steps through Stages 3 and 2. You’ve now been asleep for about 90 – 100 minutes. Then something astonishing happens: Instead of going back into Stage 1 or ‘twilight’ sleep, your sympathetic nervous system becomes more active than it is in slow-wave sleep or even when awake.

Blood flow to the brain, respiration, pulse rate, blood pressure and body temperature all increase. Your eyes dart back and forth under their lids, and you enter the highly active stage of REM sleep.

Here, messages from the brain’s motor cortex are blocked at the brainstem. As a result, muscles relax, and you’re unable to move. That’s why REM sleepers are described as having “an active brain in a paralysed body.” It’s during the first part of REM that you experience your first dream of the night. Just like clockwork [because, in fact, this entire system is run by your biological clock], you enter REM sleep every 90 minutes throughout the night.

When you’re sleeping adequately, you visit it 4 – 5 times, with each REM period being twice as long as the last. This is why your final few hours of rest are so important; they’re almost entirely REM sleep. If you’re asleep for eight hours, you’ll have spent between one-and-a-half to two hours of the night in REM.

Although dreaming can occur in all stages, about 85 per cent takes place here. REM dreams are usually the most vivid and emotional. But REM just isn’t about dreaming. The previous day’s events are solidified into permanent memory traces, and sequences of learned skills [like a new golf swing] become muscle memories in this stage.

To be wide awake, energetic, psychologically, emotionally and physiologically at your best, you must play every movement of the symphony of the night. The problem is many of us never get beyond Stage 2 sleep, due to stress, ageing or medications taken for other medical problems such as rheumatoid arthritis, hypertension or type-2 diabetes.

If you don’t sleep…

Adequate sleep is essential for performance and general health. There’s no escaping the debilitating effects of insidious sleepiness, no matter how motivated, responsible or strong you are.

Physical effects

Not sleeping makes you prone to…

Wrinkles

Sufficient sleep is required to maintain good skin texture and a healthy glow. The first area of skin to be effected by a lack of sleep is the eyelids. The skin is very thin here, so lack of sleep causes puffy eye bags, fine lines, and dark circles. In the long term, lack of sleep causes the skin to age faster leading to wrinkles, poor texture, and discoloration much earlier in life than in well-rested individuals.

During sleep, the body metabolises free radicals that accelerate ageing and cancerous growths. Without sufficient sleep, more free radicals are present in the skin leading to poor skin quality and even skin cancer. Sustained sleep deprivation impairs host defence. So, if the skin is exposed to bacteria or is healing from a lesion, lack of sleep will increase the amount of healing time required and may result in more severe bacterial skin infections.

Daytime drowsiness

This usually manifests itself as a temporary drop in energy and alertness around mid-afternoon. It’s accompanied by feelings of inattentiveness and grogginess, particularly when doing dull or repetitive tasks. It’s more likely to occur after a heavy meal or a low dose of alcohol, or while sitting in a warm room, listening to a boring lecture, or participating in a dull meeting. These factors do not cause sleepiness; they simply unmask the physiological fatigue that’s already present.

Microsleeps

These are brief episodes of sleep that you’re unaware of and that occur during waking hours. Lasting only a few seconds, microsleeps can produce inattention, resulting in accidents and injury.

Sleep seizures

These are unintended longer episodes of sleep that come on as rapidly as a seizure, occurring without warning in a severely sleep-deprived person.

Colds and flu

Jan Born at the University of Luebeck in Germany found that people who sleep less than six hours per night have 50 per cent less resistance to viral infection than those getting eight hours of sleep. In addition, Sheldon Cohen of Carnegie Mellon University found that those sleeping less than seven hours per night are three times more likely to get a cold than those who sleep longer than that.

Weight gain

Lack of sleep lowers leptin levels in the brain and raises ghrelin levels in the stomach. These hormones are responsible for regulating our appetite. When you’re sleep-deprived, you’re more likely to overeat—craving carbs, sugars and junk food. Researchers at Columbia University, USA as well as the University of Chicago, USA have found that people who sleep five hours per night have a 50 per cent higher chance of being obese, while those who sleep six hours have a 23 per cent greater risk.

Professor Francesco Cappuccio at the Warwick Medical School found that less sleep is associated with an almost two-fold increase in obesity—a trend that he says is detectable in children as young as five. The research also linked short sleep with a higher body-mass index [BMI] and waist circumference over time.

Diabetes

A study at the University of Chicago, USA involving healthy young men with no risk factor for diabetes found that after just one week of inadequate sleep, they were in a pre-diabetic state.

Researchers attributed the result to overactive central nervous systems [caused by not sleeping], which affected the ability of the pancreas to produce enough insulin to adequately regulate glucose levels.

Heart disease

Not sleeping often causes the body to produce more stress hormones. Such an imbalance can lead to arteriosclerosis, which can cause heart attacks and stroke, in addition to hypertension, muscle loss, increased fat storage, loss of bone mass, and lower production of growth hormone and testosterone.

In addition, short-sleepers miss out on REM sleep [predominant between the seventh and eighth hours of the night], during which time the heart pumps more blood to the muscles. This helps it relax as blood pressure falls. By cutting back on sleep, we’re preventing this innate regulating system from doing its job.

According to Diane Lauderdale of the University of Chicago, USA, just one extra hour of sleep per night decreases the risk of coronary artery calcification by 33 per cent. This is accompanied by a 17-mm drop in systolic blood pressure.

Cancer

Women who exercise regularly and were generally healthy had a 47 per cent higher risk of cancer if they were sleeping fewer than seven hours. Research at the Stanford University also found that good sleep habits can be a valuable weapon in fighting cancers, citing melatonin [released during sleep] and cortisol production [involved in regulating immune system activity] as vital players in recovery.

Night-shift workers [both male and female] have a 35 per cent higher risk of colorectal cancer. According to the International Agency for Research on Cancer, shift-work is a “probable” carcinogen, due to too much light exposure and the consequent lack of melatonin secretion.

Blind women have 50 per cent less risk of breast cancer than sighted women. Why? Active sighted women often stay up late, spending too much time in the light. Again, exposure to light and lack of sleep block the release of cancer fighting melatonin and raises oestrogen levels, which can cause breast cancer.

With inputs from Rebecca S Robbins and Rebecca G. Fortgang, Cornell University. Rebecca S Robbins is a doctoral candidate in communication, health and psychology at Cornell and is the co-founder of Sleep for Success. Rebecca G. Fortgang is a BA with honors in linguistics and cognitive science from Cornell University.