Signs of sleep debt found in the blood

A drop in certain fats and acids in the blood may reveal whether a person is critically sleep deprived, scientists report online February 9 in Proceedings of the National Academy of Sciences. When people and rats skimp on slumber, two compounds involved in metabolism become depleted.

A reliable marker of sleep debt could be used to test whether pilots, truck drivers and other people who hold jobs with long hours are sufficiently well rested, says coauthor Amita Sehgal, a neuroscientist at the University of Pennsylvania.

Going without sleep blunts people’s performance on memory and attention tests, and has been linked to diabetes, heart disease and other illnesses. To see how losing sleep changes metabolism, Sehgal and her colleagues took blood samples from rats and humans after they’d had only four hours of sleep a night for five nights.

In both species, two molecules involved in metabolism decreased. One is a fat that plays a role in storing energy and helping hormones send messages. The other, an acid, is a by-product of normal metabolism. Levels of both molecules bounced back after a full night’s sleep.

Sehgal and her colleagues will keep investigating these metabolic effects of sleep loss. “We’re seeing these changes in the blood, but where are they coming from and how do they relate to what’s happening in the liver, the adipose [fatty] tissue, the muscle?” Sehgal asks.