Sleep

Sleep

Maybe I should have honestly titled this section “Do as I say, not as I do.” (When I’m unconscious, I’m not as productive, I think.) Early this morning, I was already thinking: I have to get out and write the chapter on sleep! I still need to work on that.

Some people consider sleeping a waste of time, but too little sleep is associated with various acute and chronic complaints and can lead to a risk of death and disease. If you force people to get by on six hours of sleep per night for a week, you change the expression of more than 700 genes. The most severe effect can be endothelial dysfunction. The endothelium is the thin layer of cells that covers the inner surface of blood vessels and is responsible for making sure the arteries can properly relax and dilate. If subjects are randomized to sleep five hours per night for a week instead of seven, then that difference of two hours results in a marked impairment in arterial function. But how marked?

Sleep deprivation is no joke. The magnitude of the impairment after a week with five hours of sleep per night corresponds to that of people who smoke, have diabetes, or suffer from coronary heart disease. Nevertheless, more than a quarter of the population regularly sleeps at most six hours per night. Yet a sufficiently long, restorative sleep every night is an “indispensable cornerstone of health.” Still, it remains controversial whether sleep and mortality are causally linked.

It’s so green, so green

While researching for this chapter on the potential of light therapy against insomnia, I came across some extremely strange research findings—for example, “Green light extends the life of Drosophila” in the journal Experimental Gerontology. Scientists had found that they could extend the lifespan of fruit flies “sensationally,” namely by 24 percent, by raising them under green light. Conversely, they were able to shorten their lives with blue light, even in mutants without eyes! Even if the flies could not perceive the color of light at all, their lifespan was significantly affected. How?

One clue emerged when the researchers found that the green light promoted longevity far less when the flies were given an antibiotic, suggesting that it has something to do with their microbiome.

When you expose human skin to ultraviolet light, the microbiome is affected, but that is assumed to be an effect of vitamin D. In a way, it makes sense that green does flies good, because that color predominates in their natural environment. On NutritionFacts.org there are videos about the beneficial effect of “forest bathing” on humans, even though it seems more likely to come from the trees’ emissions, for example the aromatic compound pinene, and less from the colors.

Before you get carried away and buy green light bulbs, remember that in rats, for example, green light (but not red and blue) leads to glucose intolerance, which means higher blood sugar.

Sleeping Beauty sleep

There are dozens of prospective studies on sleep duration and mortality. The most common result is that there is no association at all. The second most common is that there is an association between premature death and longer sleep, usually more than nine hours per night. A quarter of the studies show a U-shaped effect, in which those who do not sleep enough (less than six or seven hours) or too much (more than nine hours) die at higher rates than those at the optimum point of seven to eight hours per night. Less than 5 percent of the results indicated only a higher risk of death for those who didn’t sleep enough. Looking at these results, it’s not surprising that a 2020 meta-analysis concluded that the only sleep category with a higher risk for older men and women concerned those who slept more than eight hours per night.

Seven hours of sleep may sound like a bit little, but presumably that is natural for our species. Scientists studied three preindustrial societies living in isolation from one another on different continents and found surprising similarities. Although they had no electric light or other electric gadgetry, people usually stayed awake until about three hours after sunset and then got up again before dawn, so that out of seven and a half hours in “bed,” they slept about six and a half. Even the studies that had found risks at both ends of the sleep-duration spectrum saw the greater risk more on the longer-sleep side.

A mechanism showing why excessive sleep harms is hard to demonstrate, which is why some scientists have rejected the idea of a causal relationship between eight or more hours of sleep per night and an increased risk of death or disease as unlikely. Could causality be reversed, with illness leading to more time in bed rather than the other way around? Maybe it is due to confounding factors such as employment status. After all, who is more likely to sleep longer? Those without work. Long sleepers (those who sleep at least nine hours per night) are more likely to live largely passively, be obese and have depression, be unmarried and have diabetes, and they have various diseases that, as confounders, could influence the association between mortality and a lot of sleep. Some studies accounted for socioeconomic status and health status, but you can’t adjust for everything. What does it all come down to? For adults aged 65 and older, the National Sleep Foundation recommends seven to eight hours of sleep per night; that corresponds to the amount of sleep associated with the lowest risk of frailty and age-related muscle loss.

Sleep well

Those who suffer from sleep apnea, a widespread consequence of obesity that disrupts sleep, may be helped by CPAP devices while they lose weight to address the underlying cause. But what if that isn’t your problem, yet you still have difficulty falling asleep or staying asleep? Check out my four rules for sleep training and sleep hygiene in the video see.nf/sleeprules. It covers techniques from cognitive behavioral therapy, as well as regulating the amount and timing of physical activity, caffeine, nicotine, and alcohol, and creating the best routines for bedtime and the sleep environment.

Risk without reward

There is a widespread misconception that older people need less sleep. In reality, sleeping simply becomes more difficult as we get older. The symptoms of insomnia increase with age and become almost 50 percent more prevalent in adults aged 65 and older, with remission rates of 50 percent over the next three years. Fortunately, insomnia does not seem to contribute to mortality risk, perhaps also because most people diagnosed with insomnia do in fact sleep more than six hours per night when their sleep duration is measured with objective methods. Twin studies found that insomnia is 40 percent heritable, meaning that our genes are responsible for less than half of insomnia risk. What can we do to influence the large part that is in our hands?