Chronic sleep deprivation: how harmful is it for weight and hormones?

After just six nights of four hours of sleep, your carbohydrate metabolism starts to go haywire. In a controlled experiment with eleven young men, blood sugar regulation deteriorated considerably, and the researchers observed effects resembling normal ageing. At the same time, the hormone that controls your thyroid (TSH) dropped. Less than one week of insufficient sleep was enough.

Your stress hormone cortisol is supposed to be low in the evening. After six nights of four hours, evening cortisol was strongly elevated (p=0.0001). Even one completely sleepless night raised cortisol by 21%. That same sleepless night lowered testosterone by 24%. More of a breakdown hormone and less of a building hormone at the same time: that is a double blow to your recovery.

Your muscles notice it directly too. One night of total sleep deprivation reduced muscle protein synthesis in thirteen healthy young adults by 18% (p=0.040). Sleep deprivation also increases your appetite and total food intake, which over time worsens your body composition.

With chronically disrupted sleep, such as in sleep apnoea, your insulin sensitivity also deteriorates. Sleep apnoea and excess weight reinforce each other in a vicious cycle. In addition, elevated cortisol drives your preference for calorie-dense and high-fat foods through reward circuits in the brain. This mechanism extends beyond sleep deprivation alone, but the overlap is biologically plausible.

Large population studies show that short sleep is associated with a higher risk of obesity, type 2 diabetes, high blood pressure and heart disease. These are not hard cause-and-effect proofs, but they fit precisely with the mechanisms found in the controlled experiments.