In addition to the damage it causes to the brain, sleep deprivation disrupts the normal function of many physiological processes, likely contributing to chronic diseases. In this chapter, we’ll cover a bevy of health issues associated with sleep deprivation.
At a high level, sleep deprivation of even just 1-2 hours triggers the sympathetic nervous system (fight or flight response) and disrupts hormonal balances. This also implies that sleep is necessary for the normal maintenance of physiology.
Many of the population studies cited in Why We Sleep are correlational - e.g. people who sleep less are more likely to have heart disease, after controlling for many other factors. But the causation is unclear - some other factors that predispose people to get heart disease (like a high baseline level of stress) could also reduce sleep.
To address this, the experimental studies cited attempt to link lack of sleep to a middle physiological state, which itself is causative for the disease. For instance, lack of sleep increases blood pressure, which the medical consensus believes is causative for heart disease.
Ideally, the “smoking gun” experiment would be to randomize people into normal-sleep and low-sleep groups for years, then observe the rate of disease. However, this is impractical (it’s hard to run very long studies like this and impossible to double-blind) and likely unethical (if low sleep is already believed to cause severe disease).
Sleep deprivation has a number of effects related to cardiovascular disease:
A population study showed that shorter sleep was associated with a 45% increased risk of developing heart disease.
An interesting finding: daylight savings time is a natural sleep experiment that typically increases or decreases sleep by 1 hour. When the clock moves forward and the population gets 1 less hour of sleep, there is a significant spike in heart attacks and traffic accidents.
Sleep deprivation reduces insulin responsiveness, which causes hyperglycemia.
In a population study, those sleeping < 6 hours a night showed higher rates of T2D (after controlling for body weight, alcohol, smoking, and other factors).
As it relates to weight, sleep deprivation:
In an experiment, subjects were randomized into a normal 8-hr sleep group, and a low 4-hr sleep group. Both groups were carefully monitored and controlled for physical activity.
One might argue that decreased sleep naturally causes more calorie burn, but an all-nighter actually consumes only 147 more calories than sleeping. Sleep is metabolically more intense than you might guess.
Finally, if you’re losing weight and under sleep deprivation, the shift of where you lose the weight from differs. When sleep-deprived, 70% of weight loss comes from lean body mass like muscles, compared to under 50% with plentiful sleep.
In males, sleep deprivation decreases testosterone, testicle size, and sperm count.
In females, sleep deprivation reduces follicular-releasing hormone (necessary for conception), increases abnormal menstrual cycles, and causes more issues with infertility.
Your face is rated as less attractive and less healthy after one night of short sleep. So there might be something to the idea of “beauty sleep.”
Sleep deprivation reduces your ability to ward off infectious disease:
Sleep deprivation increases inflammation, which increases cancer severity:
Experimental evidence:
Telomeres are a component of DNA, and they get shorter with aging. Sleep deprivation has been shown to hasten telomere shortening, thus implying an increase in aging.
(Shortform note: why would animals evolve so that sleep deprivation causes all these bad issues? Evolutionarily, consider that these responses might promote survival: in caveman days, times of low sleep may mean conditions that threaten survival (low food stores, tough weather, hostility with another tribe). The above responses might promote short-term survival - hoarding calories, activating the “fight-or-flight” system, decreasing reproduction - at the expense of long-term well-being.)