We’re often warned about getting less than 7 to 8 hours of sleep a night. Short sleepers—variously defined as people who sleep 5 hours and less or less than 6—are more susceptible than normal sleepers to a host of problems: cardiovascular disease, obesity, diabetes, cancer, and dementia. Many people with insomnia get just 5 or 6 hours of sleep a night. Rarely do we get encouraging news about our prospects for a healthy life.
But recent research on genetic mutations tells a different story. Not only does it begin to explain some of the differences in sleep duration among human beings. It also suggests that short sleep may not necessarily have adverse effects on our health and quality of life.
Short Sleep but Not Insomnia
One of these studies was published in the journal Science in 2009. In it, investigators were looking at the DNA sequences of people who naturally tended to wake up early. They located a genetic mutation in a mother and daughter who typically slept 6 to 6½ hours a night.
The women’s nights were consistently shorter than the nights of other members of their family, who did not have the mutation and who slept about 8 hours. Yet they woke up feeling well rested in the morning, with no sign of insomnia at night or fatigue during the day.
The mutation occurred in a protein (known as BHLHE41) in which one amino acid was substituted for another. This genetic variant did not interact in the usual way with nearby genes controlling circadian rhythms. So the expectation might be that this variant would have some effect on the timing of sleep, and it did. The mother and daughter were early awakeners. But it also affected the duration of their sleep, predisposing them to shorter sleep.
More Genetic Variants
Then in August 2014 another team of researchers, examining the DNA sequencing in twins and unrelated subjects, announced the discovery of 2 new genetic variants of the same protein, BHLHE41. These researchers were looking for genetic factors in humans that confer resistance to sleep loss. One of the 2 variants they identified had a big impact on both sleep and performance after sleep deprivation.
The carrier of the novel variant was a 27-year-old man whose fraternal twin, also male, did not have the mutation. The sleep-related differences between the twins were fascinating:
- The carrier twin slept an average of 5 hours a night—over an hour less than his brother.
- Despite his shorter nights, the carrier had a similar amount of nonrapid eye movement sleep (NREM sleep) as his twin. NREM sleep is composed of light sleep and deep sleep, which is associated with restorative processes.
- After going 38 hours without any sleep at all, the carrier twin slept 8 hours while his brother slept 9½. Yet an analysis of brainwaves showed that the carrier had higher delta power during NREM sleep, suggesting greater sleep drive.
Response to Sleep Deprivation
The brothers’ response to sleep loss was fascinating, too. After a full night without sleep, they underwent standardized testing every 2 hours to measure their cognitive vulnerability to sleep deprivation.
It wasn’t the more normal sleeper who fared better on the tests. It was the short sleeper—the carrier of the mutation—who had “significantly fewer average lapses of performance” on the tests. Based on these results and results of other studies, the researchers conclude that this novel variant of the BHLHE41 is associated both with short sleep and resistance to the effects of sleep loss.
Whether it also protects people from the health problems linked to short sleep remains to be seen. But regarding obesity, the study is reassuring. The body mass index (BMI) of the noncarrier twin was on the heavy side of “healthy,” but the carrier’s BMI was well within the healthy range.
We hear a lot about the problems associated with short sleep. But occasionally some bit of research comes along showing that our prospects for healthy lives may not be so bad after all.