Your mother was right: regular bedtimes and a good night’s sleep are good for you - or at least, researchers reported, irregular bedtimes and not enough sleep are bad for you.

In a 39-day experiment with healthy volunteers, shortened sleep time and varying bedtimes - meant to mimic shift work - led to impaired glucose regulation and metabolism, according to Orfeu Buxton, PhD, of Brigham and Women’s Hospital in Boston, and colleagues.

Over time, the observed changes could increase the risk of obesity and diabetes, Buxton and colleagues reported online in Science Translational Medicine.

The findings support epidemiological studies linking disrupted sleep with an increased risk of metabolic syndrome and diabetes, the researchers noted - especially in workers on the night shift.

“Since night workers often have a hard time sleeping during the day, they can face both circadian disruption working at night and insufficient sleep during the day,” Buxton said in a statement. “The evidence is clear that getting enough sleep is important for health, and that sleep should be at night for best effect.”

Most research on the issue has been observational in nature, Buxton and colleagues noted. To help fill the gap, they analyzed what happened when 21 healthy volunteers had their sleep patterns disrupted in the lab.

The participants spent 21 days before the experiment getting normal sleep - with a consistent bedtime and 10 hours in bed each night, as well as normal exposure to daylight.

In the lab, each participant lived in an individual suite for 39 days in dim light and without time cues, Buxton and colleagues reported.

For the first 5 days, they spent 16 hours a day in bed, sleeping as much as they liked. Then they faced 3 weeks of restricted sleep - no more than 5.6 hours in 24 - with sleep/wake and feeding/fasting periods that varied, based on a 28-hour “day.”

Finally, they had 9 days of “circadian re-entrainment,” in which they again had 10 hours in bed every 24 hours, with a consistent bedtime in the late evening.

At the end of each period, the researchers measured body weight, resting metabolic rate, and metabolic responses to a standardized meal.

The combination of not enough sleep and circadian rhythm disruption caused a marked decrease in insulin secretion in response to the meal, the researchers reported.

Specifically, fasting plasma insulin, postprandial peak insulin, and integrated plasma insulin concentrations were significantly reduced, by 12% (P=0.0064), 27% (P<0.0001), and 27% (P<0.0001), respectively.

That, in turn, led to significant increases in both fasting and postprandial peak plasma glucose concentrations compared with response to the same meal at baseline.

Overall, fasting concentrations increased 8% (P=0.0019) on average, postprandial concentrations rose 14% (P=0.0004), and the integrated postprandial response over 90 minutes increased 15% (P<0.0001).

The resting metabolic rate fell by 8% on average - enough to translate into a yearly weight gain of about 10 pounds a year if diet and activity levels did not change, the researchers reported.

Most of the changes reverted to baseline or near-baseline levels after the recovery phase of the experiment.

Buxton and colleagues cautioned that the study was too short to tease out the actual mechanisms behind the changes they observed.

Previous preclinical research has shown that resistance to infection is weakened depending on the 24-hour light-dark cycle of an immune protein known as toll-like receptor 9 (TLR9). And some research also has suggested that moving the clocks ahead for daylight saving time has a negative effect on circadian rhythms.

The study had support from the National Institute on Aging, the National Heart, Lung and Blood Institute, the National Center for Research Resources, the Center for Clinical Investigation of the Harvard Clinical and Translational Science Center, the Joslin Diabetes and Endocrinology Research Center Service Specialized Assay Core, the National Space Biomedical Research Institute, and the Natural Sciences and Engineering Research Council of Canada.

Primary source: Science Translational Medicine
Source reference: Buxton OM, et al “Adverse metabolic consequences in humans of prolonged sleep restriction combined with circadian disruption” Sci Transl Med 2012; (4)129ra43.