The move seemed reasonable. Five nights of insufficient sleep, followed by two mornings spent lingering in bed to repay the debt. In a study published in Current Biology on February 28, 2019, the insulin sensitivity of the group allowed to sleep freely on weekends nevertheless declined by roughly 9 to 27 percent, depending on whether it was measured across the whole body, the liver, or the muscle.
- The group that slept freely on weekends saw its insulin sensitivity fall by 27% according to the NIH.
- The study involved 36 young adults observed over two weeks in a laboratory at the University of Colorado.
- Circadian misalignment was identified as a contributing factor to the observed decline.
36 volunteers, two weeks under surveillance
The team led by Kenneth Wright and Christopher Depner, at the University of Colorado Boulder, aimed to simulate what many workers experience. They enrolled 36 healthy adults, aged 18 to 39, who stayed two weeks at the Clinical Translational Research Center on the Anschutz Medical Campus, where diet, light exposure, and sleep were closely monitored.
Three groups were formed. The first, a control, slept 9 hours per night. The second was limited to 5 hours per night, uninterrupted. The third sequence involved five nights of 5 hours, a weekend of free sleep, then two additional nights of restriction, and according to Healio, the two restricted arms counted 14 participants each, leaving eight volunteers for the control group.
Thus, the third group simulated a week of work followed by a catch-up weekend.
What the measurements showed
Among volunteers restricted to five hours of sleep per night, insulin sensitivity fell by 13% over the two weeks. In the weekend group, the decline reached 27% according to the NIH summary. The 9 to 27% range reflects that the effect was measured at three levels: whole body, liver, and muscle.
Liver and muscle: the weekend group fared the worst.
Insulin sensitivity refers to the body’s ability to regulate blood sugar levels. Wright’s earlier work had already linked sleep loss to an increased risk of obesity and diabetes, in part through this pathway. For the liver, the decline was about 23%, a result near significance in the full model (p = 0.054). The authors also estimate that weight gain contributed, in part, to the overall decrease in sensitivity of the body as a whole in this group.
66 minutes gained, and a tougher Monday
Allowed to sleep as much as they wanted, participants in the weekend group accumulated 1.1 more hours of sleep than their baseline. That is roughly 66 minutes, barely more than a TV episode. The average hides a wide spread: about 2 hours for men, about 1 minute for women.
The weekend had effects. During the recovery phase, post-dinner eating decreased. But the volunteers returned to late-night snacking as soon as the short nights resumed.
The internal clock paid the price. After two days of free sleep, the participants’ circadian rhythm had shifted, increasing the risk of waking in the middle of the biological night on Monday. Christopher Depner likens the situation to an East Coast worker flying to the West Coast for the weekend and then returning for Monday. The researchers believe this “social jet lag” contributed to the reduced insulin sensitivity in the liver and muscle.
On the balance, the two restricted groups gained about 1.4 kg.
What the study cannot claim
The limitations are clear: 36 adults, 14 in each restricted arm, all young, observed for two weeks in a laboratory. Nothing justifies extrapolating to a lifetime of sleep-ins, nor to older or ill individuals. This is a controlled protocol, not a real-life follow-up.
Kenneth Wright’s message boils down to two words: “Consistency matters.” He argues that weekend catch-up sleep does not appear to be an effective strategy to reverse metabolic disturbances tied to sleep deprivation. Christopher Depner underscores the point: you cannot sacrifice sleep without paying the price for long-term health.
A notable nuance comes from a previous study by the same team. After a simulated week at 5 hours per night, 3 recovery days at 9 hours had restored insulin sensitivity to baseline with oral glucose tests, but 5 days were not enough with intravenous tests. The measurement method thus changes the verdict, and the debate over the necessary recovery duration remains open.
Sources: healio.com | colorado.edu | nih.gov
