While sleep is a natural and necessary function and the cornerstone of good health, whether we get enough sleep, or the right kind of sleep, is another issue altogether.
In her new book, Sleep Sense: Improve Your Sleep, Improve Your Health, Katharina Lederle, Ph.D., answers all of our questions about why we don’t get enough sleep, what can interrupt our sleep, and how to improve our sleep.
“Many of us see sleep and falling asleep like flipping a light switch: if I do this and don’t do that, I’ll sleep. But it’s not that straightforward. The cycle of being asleep and being awake is complex and involves several brain areas and signaling systems,” writes Lederle.
Sleep is actually regulating by two somewhat competing drives: one to fall asleep and one that regulates the timing of sleep, much like an internal body clock.
Similarly, sleep can be divided into two separate states. Rapid eye movement (REM) is characterized by fast, wake-like waves, while non-REM sleep is characterized by longer, deeper waves.
The healthy sleeper, Lederle tells us, enters sleep through the non-REM stage, has four to six sleep cycles, has more non-REM sleep in the first third of the night, has more REM sleep in the last third of the night, spends about 75 percent of sleep time in non-REM sleep, and spends about 25 percent of total sleep time in REM sleep.
However, sleep is not as predictable as we might imagine. Lederle writes, “What’s important to realize is that there is no one bedtime that’s best for all of us.”
One way to find out what our individual sleep timing is, says Lederle, is to take a five-day holiday and allow ourselves to sleep and wake as our body tells us to.
She writes, “It’s likely that your body will use the first three to four days to recover from any sleep debt you have accrued in the past. After the fourth or fifth night, you’ll know when you sleep best.”
Age, genes, and sleep chronotype all play a role in determining just how much sleep we need, which is not always eight hours.
“Your sleep behavior changes as you go through life. Neither the amount of sleep needed and the different sleep stages, nor the timing of your sleep stays the same,” writes Lederle.
Sleep transitions — from sleeping to waking — can also have individual differences as some people will be more prone to grogginess in the morning, also known as sleep inertia, than others.
One way we can help our internal clock in the morning (and also combat jet lag) is to expose ourselves to light.
Lederle writes, “Light exerts its effect on sleep and wakefulness in two ways: by synchronizing your internal clock with the day and by promoting alertness.”
Yet if we find ourselves in chronic sleep debt, our health and well-being can be adversely affected.
Lederle points to the connection between weight gain and sleep deprivation. She writes, “Several research groups have set out investigate what happens to leptin and ghrelin when people are kept awake for longer periods or the entire night. While the exact findings are mixed, one main hypothesis is that when you stay up late at night, levels of ghrelin and leptin get out of balance. If this is true, then the altered relationship is likely to stimulate your appetite, so you become hungry and eat more during the night.”
The reward we derive from food — our hedonic drive in action — is also greater when we are sleep deprived, meaning that the perceived value of the foods we consume is greater.
“It’s because the brain believes we’re in a survival-critical situation. Why else would we be awake and depleting our energy levels?” writes Lederle.
Cortisol levels are also elevated when we are sleep deprived, which can cause a pseudo-diabetic state when insulin levels are artificially high due to lack of sleep.
Lederle points to a recent study that found that sleeping five hours a night for five days reduced insulin sensitivity, and while three nights of nine hours’ sleep restored some insulin sensitivity, insulin was still not at normal levels.
Lack of sleep or poor quality sleep also affects our cognition, memory, immune response, and emotional functioning, and we are often poor judges of our own sleep needs. Lederle suggests creating a sleep environment that is cool, dark, and quiet. However, quality sleep also depends on what we do during the day.
Regular wake times, early exposure to sunlight, exercise, healthy nutrition, and giving ourselves permission to feel tired, to relax, recover, and regenerate are all ways we can improve our sleep — and maybe even recover some lost sleep.
Drawing on her extensive background as a human sleep and fatigue specialist, Lederele takes us through the science of good sleep, why sleep is so important, and how to get more of it.
Sleep Sense: Improve Your Sleep, Improve Your Health
Exisle Publishing, June 2018
Paperback, 232 pages