People who have irregular sleep patterns and/or do not sleep enough have a higher risk of developing metabolic syndrome and diabetes, researchers from Harvard Medical School, and Brigham and Women’s Hospital in Boston, reported in the journal Science Translational Medicine.
Orfeu Buxton, PhD. and team examined healthy volunteers over a 29-day period. They were made to sleep less and at varying bedtimes; sleeping patterns similar to those experienced by shift-workers.
They found that the shift-like sleep patterns led to poorer glucose regulation and metabolism. The authors explained that eventually, over time, the raised risk of obesity and diabetes became apparent.
Previous observational studies had associated disrupted sleep patterns with a higher risk of developing diabetes and metabolic syndrome, especially among night-shift workers. The researchers say their findings confirm this.
“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. The evidence is clear that getting enough sleep is important for health, and that sleep should be at night for best effect.”
As most previous research had been epidemiological, Buxton and team decided to examine for themselves what might happen to 21 healthy individuals if their sleep patterns were disrupted in the laboratory.
For 21 days before their experiment began, the volunteers slept normally – a total of 10 hours in bed each night. They were also exposed to normal periods of daylight.
Then, each volunteer went into an individual suite in the lab for 39 days – there were no time cues, and the lighting was dim.
They spent 16 hours each day in bed during the first five days, with no limitation on the amount of sleep they wished to have. This was followed by 21 days of a maximum of 5.6 hours of sleep during every 24-hour cycle. Their sleep/wake and eating/fasting routine was based on a 28-hour day.
For the last nine days they underwent “circadian re-entrainment” – ten hours in bed every 24-hour cycle, going to bed at the same time each evening.
At the end of each stage of the experiment, the volunteers’ vitals were measured, including their resting metabolic rate, body weight, and metabolic responses to a standardized meal.
The authors found that when subjected to circadian rhythm disruptions and sleep deprivations, there was a considerable drop in insulin production after meals.
Insulin concentrations, during fasting periods, after meals, as well as integrated plasma insulin concentration dropped considerably, by an average of 12%, 27% and 27%, the researchers explained.
This resulted in considerable rises in fasting as well and after meal peak plasma glucose concentrations, versus responses to the same meal at the start of the study. Fasting concentrations increased, overall, by an average 8%, after-meal concentrations by 14%, and the integrated postprandial response over 1.5 hours rose by 15%.
Their resting metabolic rate dropped by an average of 8%, which translates into an annual weight gain of approximately 10 pounds (if diet and physical activity remained unchanged), the authors wrote.
During the nine-day recovery phase of this experiment, most changes returned to baseline levels.
The authors emphasized that in order to find out what actual mechanisms behind the observed changes might be, a much longer study is required.
Previous studies had demonstrated how people’s immune system may be affected by alterations in the 24-hour light-dark cycle of TLR( (toll-like receptor 9), an immune protein. Put simply, individuals’ resistance to infections were affected. Some studies suggest that putting clocks forward for daylight saving time has a detrimental effect on circadian rhythms.
Written by Christian Nordqvist