New research from the US suggests that sleepiness could be in our genes, and may partly explain why some people seem able to remain fresh and alert on four hours sleep a night.
The researchers found that after several nights of restricted sleep, healthy adults who carried a particular gene variant called DQB1*0602 were sleepier and more fatigued during the day, and had more fragmented sleep, than non-carriers.
The variant is closely linked to narcolepsy, a sleep disorder that makes people feel sleepy during the day. But the researchers said carrying the variant does not mean you develop the disorder: depending on the population some 12 to 38 per cent of carriers do not have narcolepsy, and have no sleep problems. And while it is less common, some people can still develop the disorder even though they do not carry the variant.
You can read about the study, led by Dr Namni Goel, assistant professor of Psychology in Psychiatry at the University of Pennsylvania School of Medicine in Philadelphia, in the 26 October online issue of Neurology, the medical journal of the American Academy of Neurology (AAN).
Goel told the press that if their findings are confirmed, it could justify recommending that carriers of DQB1*0602 take naps or caffeine to help them cope during times of sleep restriction.
For the study, the researchers recruited 37 healthy adult carriers of the DQB1*0602 gene variant and 92 healthy adults that did not have it and observed them for a week in a sleep laboratory. None of the participants had any sleep disorders.
For the first two nights the participants spent 10 hours in bed and were fully rested.
For the next five nights, their sleep was restricted: they underwent “chronic partial sleep deprivation“, where they were only allowed four hours in bed every night. For the rest of the time the lights stayed on and they could read, play games or watch films, to help them stay awake.
Over the week, the researchers measured the participants’ sleep quality, asked them to rate their sleepiness, and complete tests to assess memory, attention and ability to resist sleep during the day.
The results showed that:
- Carriers of DQB1*0602 had a lower desire to sleep (sleep drive) during the fully rested nights.
- During the second fully rested night, carriers had an average of 34 minutes in stage 3 sleep, while non-carriers had an average of 43 minutes.
- During the fifth night of restricted sleep,carriers spent an average of 29 minutes in stage 3 sleep, compared to 35 minutes for non-carriers.
- Carriers of DQB1*0602 were sleepier and more fatigued than non-carriers, and their sleep was more fragmented: both when they were fully rested and when sleep deprived.
- For example: carriers woke on average four times on the fifth night of restricted sleep, while non-carriers woke on average only twice on that night.
- Carriers spent less time in deep sleep than non-carriers: both during the fully rested nights and the sleep restricted nights.
- There was no difference between carriers and non-carriers of DQB1*0602 in memory and attention performance, and in their ability to resist sleep during the day.
The researchers concluded that DQB1*0602 was linked to differences among individuals in a number of physiological measures of sleep, sleepiness and fatigue, but not in cognitive measures; both during baseline (the rested nights) and during chronic partial sleep deprivation.
“DQB1*0602 positivity in a healthy population may represent a continuum of some sleep-wake features of narcolepsy,” they wrote.
Goel said the gene variant may be a “biomarker for predicting how people will respond to sleep deprivation, which has significant health consequences and affects millions of people around the world”.
For example, it could be very important to night shift workers, people who frequently travel across time zones, or people who have a lot on their hands with work and family commitments, said Goel, who stressed that more studies should now be done to confirm the findings.
Funds from the National Space Biomedical Research Institute, the National Institutes of Health, the Institute for Translational Medicine and Therapeutics and the National Center for Research Resources, helped pay for the study.
“DQB1*0602 predicts interindividual differences in physiologic sleep, sleepiness, and fatigue.”
Namni Goel, Siobhan Banks, Emmanuel Mignot, and David F. Dinges.
Neurology, 26 October 2010; 75(17): 1509-1519.
Additional sources: Penn Medicine, AAN.
Written by: Catharine Paddock, PhD