Recommendation: Figure out how to sleep 7-8.5 hours per night. For me, that meant finding out how exercise and diet help me get to sleep so I’m not laying there for 30 minutes. I also realized that I didn’t feel like I lost an hour of productivity when I force myself to get enough sleep. You’ll still get what’s important done, and–by definition–become more efficient at those tasks.
Sleep and gut health
We know that most of the cells in our body are not human. ((Microbial Ecology…)) This has led to research of the interaction between the brain and the gut, known as the GBA (Gut-Brain Axis). Though this interaction has been studied for over a decade, I was not able to find enough research to show that inadequate sleep directly alters gut health in humans. However, there is evidence that it happens in mice. We do have evidence that altering the sleep cycle can affect the gut, but this effect only becomes significant when a 2nd condition (stress, poor diet, etc.) is introduced. ((Circadian Disorganization…)) While this doesn’t directly link sleep to gut health, it’s been shown many times that poor sleep habits correlate with various metabolic issues (especially leptin/ghrelin imbalance and positive energy balance) ((Short Sleep Duration)) ((The metabolic consequences…)) Therefore, sleep debt–generally defined as getting less quantity, not necessarily worse quality sleep–is the first step on a path that probably leads to impaired gut health.
Inflammation/immune system
The immune system is undoubtedly harmed by sleep debt. ((Sleep and Host Defense)) I’m not concerned with total sleep deprivation, as that’s obviously horrible for you. I am more concerned about my health when I only get 6 hours a few times per week, in other words, I want to know at what point it starts to affect my health. One study tested the effect of 1 week of 6-hours of sleep per night. It caused a significant increase in two major inflammation markers (IL-6 and TNF-alpha) in Men, though it didn’t see it with TNF-alpha in Women. ((Adverse effects of modest…)) Luckily, a meta-analysis of 10 studies 2004-2012 provides some further insight. This type of analysis is important because as one author put it, “pro-inflammatory cytokines, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1 β, IL-6, IL-8, IL-12, IL-17, IL-18, in balance with anti-inflammatory cytokines (interferon [IFN]-α, transforming growth factor [TGF]-β…) are essential mediators of the inflammatory system.” These studies ranged from 7 days of 6 hours of sleep each night to 1 night of 2 hours of sleep. Each study resulted in a significant effect on inflammatory/immune or both systems (they are related systems, but what specific markers are measured differs). Immune response (leukocyte/monocyte/neutrophil counts) increased in three of the studies. Inflammation markers (usually IL-6, TNF-alpha, and CRP) increased in all but two of the studies. These effects were not entirely erased by one night of 8-hour sleep; immune markers remained above baseline, but it did significantly reduce them. Interestingly, a 30-minute nap the day after 1 night of 2-hours of sleep had a measureable benefit on immune markers. I think the most important finding is that, “sleeping 6 h/night for 7 consecutive days, was associated with increased 24 h secretion of IL-6 in a group of healthy young men and women”. ((Immune, inflammatory, and cardiovascular…)) 6 hours per night is probably above average, from what I hear among college students. This segment, which typically doesn’t eat well either, is then potentially put in a state of chronic inflammation. Further research has shown the result of these effects after vaccination. One showed “healthy subjects with regular sleep after vaccination displayed a nearly two-fold higher hepatitis A virus antibody titer after 4 weeks than subjects subjected to total SD the night after vaccination.” ((Sleep enhances the human…)) Another showed that sleep restriction (4 hours/night for 6 nights) cut the beneficial immune response to vaccination in half compared to subjects with 7.5-8.5 hours. ((Effects of sleep deprivation…)) Another study aggregated evidence that sleep–and its various cycles–plays an important role in overall regulation of cytokine production. ((Effects of sleep and circadian)) Also, the time spent in each sleep cycle is kept in similar proportion regardless of how long we sleep. In other words, the body knows how much time it needs to spend in each cycle. The conclusion is that both single-night and chronic sleep restriction have inflammatory and immune effects on the body (sleep restriction is usually 6 or fewer hours). Considering inflammation contributes to atherosclerosis, diabetes, and cardiovascular disease I think there are plenty of reasons to value that extra hour of sleep more than whatever I would’ve done instead. There is even greater concern when behavioral factors, such as poor diet, smoking, alcohol abuse or over-exercising are present; these can also influence the inflammatory process. ((Immune, inflammatory, and cardiovascular…))
Sleep and endocrine function
Endocrine function is also harmed by sleep debt. ((Impact of sleep debt)) We know that, “the activity of the two major stress-axes—the hypothalamus pituitary adrenal (HPA) axis and the sympathetic nervous system (SNS)—with their respective effector hormones cortisol and catecholamines (epinephrine and norepinephrine) is suppressed during nighttime and by sleep”. ((Effects of sleep and circadian…)) In fact, even a 30-minute afternoon nap reduces cortisol levels. ((Benefits of napping…)) Therefore, it wasn’t suprising to find that 6 nights of 4-hours of sleep significantly raised average cortisol levels in the afternoon and evening. ((Impact of sleep debt…)) Furthermore, hormonal effects of 2 days of sleep restriction are seen via an 18% decrease in leptin (tells you you’re full) and 28% increase in ghrelin (tells you you’re hungry). ((Sleep curtailment…)) In other words, you feel hungrier and eat more. Speaking of which…
Sleep and the metabolism
Don’t eat a high-carb diet if you don’t get adequate sleep–less than a week of 4-hour nights put healthy young subjects into such poor glucose tolerance/effectiveness states that they were in the range of insulin impaired/non-insulin dependent diebetic populations. ((Impact of sleep debt)) An epidemiological study of about 1500 people found that 6 hours per night increased chances of diabetes 66%, and 5 hours per night more than doubled it. ((Association of sleep time…))
Conclusion
It’s scary to think how damaging inadequate sleep could be when I consider how easy it is to let serious issues go unnoticed. More likely is that health issues are unassociated with a lack of sleep, simply because this research isn’t common knowledge yet. As sleep debt accumulates, resulting issues are attributed to diet or genetics (which, of course are significant factors) instead of the minor loss of sleep repeated daily. Furthermore, we feel like we can get by on little sleep by drinking caffeine, neglecting to seek to first learn what affect a drug so strong may have on us over time. Schools, especially universities–supposed centers of enlightenment–are obligated to coach students in health as a means to facilitate learning, which is the point of their enrollment, but I have yet to see any research-based emphasis on proper sleep. Maybe instead of a weight-loss challenge, we could design a sleep-gain competition; napping is way easier than going to the gym, anyway.