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Bad sleep, 25% more insulin resistance
A single bad night raises cortisol and inflammation on top of the added insulin resistance. It also lowers leptin, the hormone that signals fullness and tells the body to burn fat, so cravings get worse the next day. These women had no idea how much sleep affected their bodies until they started prioritizing it.
Hydration worked the same way. When a person is dehydrated, everything slows down: detoxification drops, the body holds on to fluid, and inflammation rises. These are fundamentals everyone thinks they already have covered, and the women tracking them found they hadn't been consistent.
How does one bad night affect insulin?
In a 2010 Dutch study, Esther Donga and colleagues found that healthy volunteers who slept four hours for a single night had reduced insulin sensitivity the next day. Insulin sensitivity measures how well the body's cells respond to insulin's signal to take up glucose. Earlier work by Eve Van Cauter's group at the University of Chicago had found that several nights of short sleep impaired glucose tolerance in healthy young men.
How was leptin discovered?
Leptin was identified in 1994 by Jeffrey Friedman's lab at Rockefeller University, which cloned the gene that mutant obese mice lacked. It is made mainly by fat cells and acts on the hypothalamus to signal long-term energy stores. Mice missing the gene eat constantly and become severely obese. A few rare human families with leptin deficiency show the same pattern.
How does sleep loss raise cortisol?
In a 1997 study in the journal Sleep, Rachel Leproult, Eve Van Cauter, and colleagues found that sleep deprivation raised cortisol levels the next evening in healthy volunteers. Cortisol normally falls to its lowest point around the start of sleep, so a higher evening level means the daily rhythm had flattened. The researchers linked the change to disrupted regulation of the body's stress system.
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