Health Blog: How Too Little Sleep Weakens Immunity

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We may have underestimated the impact of sleep on our immune defenses.  A growing body of research suggests that sleep deprivation may weaken our barrier defenses ­­– the first line of defense against bacteria. 

Pursuing this line of investigation, scientists from the University of Tennessee, College of Medicine wanted to understand to what extent sleep deprivation could trigger this sometimes-fatal migration of bacteria into the bloodstream.[i]  In this provocative study, animals were subjected to sleep deprivation over a period of twenty days. Each animal was matched with a paired control that was not sleep deprived, which permitted a direct comparison. At five, ten, fifteen and twenty days, the rats were tested for bacterial counts in their lymph nodes, bloodstream, and organs.

In order to count bacteria, scientists use the term colony-forming units (cfu). Colony forming unit is a measure of living cells, where a colony represents a group of bacterial cells that grow from a single parent cell. The higher the CFUs, the greater the bacterial invasion.

Ordinarily, when bacteria migrate from the intestine to the interior of the body, they pass first into the lymph nodes, which serve as a launch point for dissemination to the bloodstream and to organs such as liver, kidney, spleen, and lung.  One of the first sites invading bacteria from the colon can be found is in the mesenteric lymph nodes – specifically, the lymph nodes associated with the abdominal organs. This, as expected, was the site where migrating bacteria were first detected. By day twenty, the inguinal lymph nodes (comparable to lymph nodes in the groin in humans) of all the sleep-deprived animals contained from 330 to 40,700 CFUs per gram of tissue. This was compared to only 660 CFU in only one of the control animals.

Lack of sleep makes bacteria count skyrocket 

The cecum is a pouch where the small intestine meets the large intestine. It normally contains an abundance of bacteria, though it contains fewer numbers than those found in the colon. When bacterial populations were cultured after twenty days of sleep deprivation, the gram-negative aerobic bacteria were thirty-sevenfold higher in the sleep-deprived rats than in the animals not deprived of sleep.  The levels of the bacterium E. coli in the ileum (the end portion of the small intestine) increased twenty-one-fold in sleep-deprived rats after twenty days, compared to controls.

According to Dr. Carol Everson at the University of Wisconsin, “In our animal model, impairment of host defenses is chief among sleep deprivation outcomes, as evidenced by strikingly poor control over indigenous micro-organisms despite an outwardly healthy appearance and robust appetite.”[ii] [emphasis added]

To understand the implications, it is useful to think of the gut barrier as a dike that holds back the microbe-laden waters of the large intestine. Our system of defense is organized to keep these bacteria on other side of the dike. We do this by strong cell-to-cell junctions, a mucus layer, a water layer, immune cells, antibodies, and a range of other protections. Dr. Everson’s studies suggest that sleep deprivation weakens the dike until it is breached, allowing bacteria-contaminated waters to rush to the other side – to the interior of our body. Once the whole bacteria or endotoxins (fragments of dead bacteria) break through the dike, however small the numbers, our systemic immune system must engage to protect us.

If these conclusions by Dr. Everson and colleagues hold true, it represents a remarkable advance in our understanding of factors that may strengthen or weaken our defense against microbes. This knowledge can be used as part of an organized and sophisticated effort to strengthen immunity, reduce antibiotic use, and to stand strong in the world of the microbe. 

Next: How bacteria use our own molecules to have their way with us, and what we can do to prevent it.

© 2010 Michael A. Schmidt, Ph.D.

You can read Michael Schmidt's next health blog, How Bacteria Use Our Own Stress Molecules, here. 

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[i] Everson, CA, Toth, LA. Systemic bacterial invasion induced by sleep deprivation. Am J Physiol Integrative Comp Physiol 2000;278:R905-R916.

[ii] Everson, CE. Clinical assessment of blood leukocytes, serum cytokines, and serum immunoglobulins as responses to sleep deprivation in laboratory rats. Am J Physiol Rgul Integr Comp Physiol 2005;289:R1054-63.