Sleep and metabolism

Sleep is important in regulating metabolism. Mammalian sleep can be sub-divided into two distinct phases - REM (rapid eye movement) and non-REM (NREM) sleep. In humans and cats, NREM sleep has four stages, where the third and fourth stages are considered slow-wave sleep (SWS). SWS is considered deep sleep, when metabolism is least active.

Metabolism involves two biochemical processes that occur in living organisms. The first is anabolism, which refers to the build up of molecules. The second is catabolism, the breakdown of molecules. These two processes work to regulate the amount of energy the body uses to maintain itself. During non-REM sleep, metabolic rate and brain temperature are lowered to deal with damages that may have occurred during time of wakefulness.

After eating, the pancreas releases insulin. Insulin signals muscle and fat cells to absorb glucose from food. As a result, blood glucose levels return to normal.

Insulin-Resistant Metabolism

Baseline levels of insulin do not signal muscle and fat cells to absorb glucose. When glucose levels are elevated, the pancreas responds by releasing insulin. Blood sugar will then rapidly drop. This can progress to type 2 diabetes.

Sleep loss can affect the basic metabolic functions of storing carbohydrates and regulating hormones. Reduction of sleep from eight hours to four hours produces changes in glucose tolerance and endocrine function. Researchers from the University of Chicago Medical Center followed 11 healthy young men for 16 consecutive nights. The first 3 nights, the young men slept for the normal 8 hours. The next 6 nights, they slept for 4 hours. The next 7 nights, they spent 12 hours in bed. They all had the same diet. They found that there were changes in glucose metabolism that resemble that of type 2 diabetes patients. When the participants were tested after sleep deprivation, they took 40% longer than normal to regulate blood sugar levels after a high-carbohydrate meal. The secretion of insulin and the body's response to insulin decrease by 30%. Sleep deprivation also alters the productions of hormones, lowering the secretion of thyroid stimulating hormone and increasing blood levels of cortisol.

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