Researchers working with under slept rats and humans reveal how signs of sleep debt show up in the blood. The findings, published in Proceedings of the National Academy of Sciences this week, can help us understand the various dysfunctions that come with chronic sleep restriction.
To better understand the molecular mechanisms underlying sleep loss, a team led by Aalim Weljie from the University of Pennsylvania restricted rats and healthy human recruits to only four hours of sleep per night for five days. Sleep restriction is different from sleep deprivation in that sleep time is curtailed, but not eliminated. "Sleep restriction more closely represents real-world situations in humans and is a condition experienced by millions of people every day," Penn’s Amita Sehgal says in a news release. In people, not sleeping enough has been associated with metabolic disorders like weight gain, diabetes, obesity, and cardiovascular disease. "One possibility is that sleep drives metabolite clearance and so acts as a reparative process at the metabolic level," Sehgal adds.
Next, the team analyzed the serum from both under slept rats and humans, as well as from adequately-slept control groups, and created a comprehensive profile of metabolites, the end products of metabolism. Half of the 38 metabolites unique to sleep-restricted rats were known lipids, and the majority of the metabolites from the sleep-restricted humans were also lipid or fatty acid-related compounds.
Compared to the sufficiently rested groups, sleep-restricted individuals of both species showed significantly decreased levels of oxalic acid and diacylglycerol 36:3 and increased levels of phospholipids.
Oxalic acid is a waste byproduct of processing foods and breaking down vitamin C and amino acids, and diacylglycerol is a precursor molecule in the production of triglycerides: which helps store fat in the body and signal cells. Both depleted metabolites were restored after recovery sleep, and the researchers think they could serve as cross-species biomarkers of sleep debt. As for the increase in phospholipids, "while we don't yet know why the lipids are changed in both species, these shifts are very intriguing, given the epidemiological links between restricted sleep and metabolic disorders," Weljie says. "I'm sure there's a connection."