Young healthy volunteers were studied in the sleep laboratory of the Insitute of the Occupational Health. For the two first days they slept their normal 8 hours sleep, and after that, half of them continued to sleep normally and half restricted their sleep to 4 hours during five consecutive days. After that they were allowed to sleep normally for 2 more nights (see picture: Desigh of the Experiment). During the day, they performed for two hours a multi task with four different tasks simultaneusly on the screen (see picture: Multitask score). Success score was calculated every 20 min. Blood samples were collected during the baseline day (BL), after 5 days of sleep restriction (SR) and after the 2 day recovery (REC).
The results show that sleep restriction activated immune defense: the clinical marker for inflammation, CRP, was increased, as well as cytokine responses. Also the white blood cell counts were affected, and expression of many immune response-related genes and gene pathways was elevated. In summary, sleep restriction created a condition of low-grade inaflammation.
Glucose metabolism showed decreased blood glucose levels while the insuline levels were increased, resulting in increased insuline/glucose ratio, which is regarded to be a risk factor for developing type 2. diabetes.
Many parameters regulated by the autonome nervous system were also affected
Expression of genes and gene pathways releated to reverse cholesterol transport were down-regulated, and together with increase in immune response, this is compatible with potential decrease in LX-receptor functioning. LX receptor regulates lipid metabolism, reverse cholesterol transport and immune responses.
As both low-grade inflammation and abnormal cholesterol metabolism and transport are risk factors for atherosclerosis, we hypothesize that these mechanisms could explain the epidemiological finding that short/bad quality sleep is associated with increased risk of atherosclerosis.
Multitask performance deteriorated gradually during the five sleep restriction days, while in controls it remained at the base line level. Interestingly, the scores in the beginning of the test session remained at relatively high level, but by the end of the session, the scores decreased, quite dramatically during the two last days of sleep restriction.