Sleep deprivation affects the immune system — this has long been believed by scientists. A new study revealed: correct, but different than expected.
You could call it a waste of time: humans sleep through about one-third of their lifetime. Much could be accomplished during these hours. But the truth is, these hours are not wasted at all, because the nightly time-out is one of the prerequisites for health, performance, and well-being, and is as important as healthy food. Persistent sleep deprivation instead, draws on quality of life, undermines the body, and results in cardiac problems, obesity, diabetes, and worse. Rats that were deprived completely of sleep finally died miserably.
Scientists speculate that the immune system may be responsible for the detrimental effects of sleep loss. Until recently, some of them believed that a lack of sleep may activate the immune system, as this was concluded from some studies. However, sleep deprivation was predominantly studied in sleep laboratories. That this may be different under real-life conditions was what researchers such as Nathaniel Watson and colleagues from the University of Washington now had to acknowledge; they observed the contrary (1).
For their investigation, they selected 11 identical (= monozygotic, MZ) twin pairs. One of the prerequisites was that their average sleeping behavior (duration) had to be different for at least 1 hour. Thereby, the scientists could exclude that genes play a role for the difference in sleep duration since MZ twins do not differ in their set of genes, almost completely. Also, former influences of the family were excluded since both twins grew up together. Differences in sleep behavior, therefore, must be due exclusively to individual environmental factors, such as their working situation.
They then recorded the activity patterns of the volunteers for two weeks using an actigraph, a scientific tool comparable to a smartwatch or a fitness tracker, that monitors movements via a sensor, and they had to keep a sleep diary.
Two weeks later, blood was taken. To investigate the influence of the immune system the scientists focused on leucocytes. These are the white blood cells that play an important role in immune defense. They isolated leucocytes from the blood and investigated gene expression of leucocytes via microarrays. Genes contain the blueprint of certain molecules, mostly proteins. To build these proteins, they must be read beforehand. This method allows to identify those genes in the whole human genome (or fractions thereof, e.g. known for the relevance in immune regulation) where this happens.
It became evident that in twins who slept less, those genes and signaling pathways were suppressed that are relevant for an immune response and an inflammatory reaction — this is not what Watson and colleagues had expected. So they compared their results to data from other publications on the same topic.
During a Finnish study (2), nine healthy young males were allowed only 4 hours of sleep every night for one week, while staying at the laboratories of the Finnish Institute of Occupational Health. Before and after sleep deprivation, gene expression of the white blood cells were investigated. These results were compared to data from 4 men that were allowed 8 hours of sleep every night. In those with sleep deprivation, eight of the 25 most upregulated gen transcriptions were directly associated with the immune system. In addition, 15 of the 25 most affected metabolic pathways were linked to immune functions.
The difference between the two studies could not be more pronounced. When sleep is interrupted short-term under laboratory conditions, the body responds with an activation of the immune system and inflammation responses. When subjects always sleep rather short under regular, natural conditions, the opposite happens.
However, Watson’s study included only 22 volunteers and, thus, was rather small. And the measured differences in gene expression was as well and did not even double or bisect. Whether chronic sleep loss, therefore, suppresses immune activation and its signaling pathways will have to be shown by further and future investigations.
This is part 11 of a series covering twin health provided by Paul Enck from the Tübingen University Hospital and science writer Nicole Simon. Further studies in twin research can be found at TwinHealth website.
References:
- Watson NF, Buchwald D, Delrow JJ, Altemeier WA, Vitiello MV, Pack AI, Bamshad M, Noonan C, Gharib S. Transcriptional Signatures of Sleep Duration Discordance in Monozygotic Twins. Sleep. 2017 Jan 1;40(1). doi: 10.1093/sleep/zsw019.
- Aho V, Ollila HM, Rantanen V, et al. Partial Sleep Restriction Activates Immune Response-Related Gene Expression Pathways: Experimental and Epidemiological Studies in Humans. PLoS One. 2013 Oct 23;8(10):e77184.