And now for a subject I hate even thinking about: sleep. Unlike most people, I dread going to sleep at night. I’m a terrible sleeper: I wake up over and over, sometimes falling back to sleep quickly, but all too often, not. I can’t tell you how often the thought,“Will this night never end” has gone through my head.
Anyone who is a bad sleeper totally understands why sleep deprivation was used as a form of torture.
I’ve been reading a lot, over the last few years, about the ties between sleep and inflammation/inflammatory diseases. An article a few days ago really caught my eye. It turns out that pro-inflammatory cytokines like interleukin-6 seem to be the link between sleep and the gut microbiome: you can thank your depleted biome for that bad night’s sleep, which results in higher levels of these inflammatory chemicals.[i]
We know that during deep sleep, the brain cleanses itself. Lack of deep-sleep time, in the short-term, is associated with stress and psychological problems. In the long term, it is associated with cancer, cardiovascular disease, autoimmune illnesses, and more.
26 male subjects had their sleep habits measured (average bed time, wake time, total time in bed, total time actually asleep, length of time to fall asleep, number of awakenings, and so forth). They also donated saliva and stool samples, in order for the researchers to track the relationships.
Sleep efficiency and total sleep time are positively associated with bacterial microbiome diversity and richness. (“Sleep efficiency is the percentage of time spent asleep while in bed.”[ii]) Wake after sleep time was negatively associated with bacterial diversity. (So, the less diverse your bacterial microbiome, the more time you spend not sleeping after those night wakings. (I’m in trouble.)) The researchers conclude: “We found that microbiome diversity…was positively correlated with sleep efficiency, and total sleep time, and was negatively correlated with the sleep fragmentation.” In other words, those with richer and more diverse microbiomes slept better. And since better sleep means better health, those who don’t sleep well are caught in a vicious cycle. So yeah – those of us with poor sleep were also found to have higher levels of pro-inflammatory IL-6: “…high daytime serum concentrations of IL-6 is associated with poor sleep quality. In addition, increased IL-6 levels are associated with fragmented sleep in mice. IL-6 is also an important factor in sleep regulation as sleep onset often coincides with increased circulating IL-6 and IL6 remains high during the night.”
(For those of you unfamiliar with IL-6, dysregulation of this pro-inflammatory cytokine is highly associated with autoimmune diseases like rheumatoid arthritis, juvenile arthritis, osteoporosis, and psoriasis. It’s considered critical in the initiation of autoimmunity.)
A few especially interesting notes:
The take-away message is that there most certainly is an association between bacterial microbiome diversity and sleep quality, as well as inflammation. And, as I mentioned above, while the IL-6 levels were not directly associated with stress, loss of gut bacterial diversity IS associated with stress, as well as many other factors. Once again, we are left with little direction as to how to break out of the vicious cycle (bad sleep leads to bad health and bad health leads to bad sleep). Working on improving diet, stress reduction, exercise, and so forth are, for the moment, our only options.
[i] Smith, R. P., Easson, C., Lyle, S. M., Kapoor, R., Donnelly, C. P., Davidson, E. J., … Tartar, J. L. (2019). Gut microbiome diversity is associated with sleep physiology in humans. Plos One, 14(10). doi: 10.1371/journal.pone.0222394