Sleep lets our body processes rest and restores us for the next day, so a bad night's sleep can ruin the following twenty-four hours and even make us feel sick. Now, new research published in the journal Sleep cements the idea that loss of sleep actually leaves us vulnerable to sickness.
The National Institutes of Health suggest that adults get 7-8 hours of sleep each night to avoid what they call "sleep debt." But how much sleep we actually need is determined by many factors—with genetics responsible for 31-55% of our sleep patterns. And work schedules, new babies, checking that last email, Netflix binges, and innumerable other forces related to our habits and surroundings work to keep us from getting a good night's sleep.
It's not uncommon to feel like we get sick more when we aren't getting enough sleep, and studies have shown that short sleep is associated with many adverse health outcomes including cognitive, metabolic, cardiovascular, and immunological impairment.
The new research, led by Dr. Nathaniel Watson, co-director of the UW Medicine Sleep Center at Harborview Medical Center, studied identical twins, and found that the twin who consistently slept only an hour less a night than their twin showed disruptions in genes that govern their immune system.
There have been two main problems with previous research linking sleep loss to lowered immune function that Watson and his team sought to clarify in their study.
The first was the big influence of genetics in how much sleep we need. Using identical twins in their study eliminated differences in sleep patterns controlled by genetics. By studying the sleep habits of 11 pairs of identical twins who reported differences of sleep time of one hour or more per night, the researchers picked genetically identical subjects to study.
Additionally, previous sleep studies used extreme sleep deprivation to look for health effects, but this group observed the twins' sleep patterns in their homes using a device on their non-dominant wrist to measure their sleep times. Nighttime sleep time was added to daytime nap times for 14 days, and averaged to calculate the mean sleep time per person.
The average daily sleep time of all the twins in the study was 7.3 hours, but between the twin pairs, there was a 64 minute difference—one twin regularly slept about an hour less than the other. The survey did not ask why the participants slept for that amount of time, so the researchers couldn't say if these twin who slept less did so because they felt they didn't need to, or if it was because of social and work constraints. The twins who slept less did so routinely and did not report any negative health effects from their sleep habits.
Blood samples taken from the twins showed that genes involved in the immune response, which alert cells to an infection and activate them to fight it, were turned down in the twins who regularly slept about an hour less. Genes that are turned down function less or with less efficiency.
The results are consistent with studies that show when sleep deprived people are given a vaccine, there is a lower antibody response, and if you expose sleep deprived people to a rhinovirus they are more likely to get the virus.
The Centers for Disease Control and Prevention reported that nearly 30% of adults who participated in the National Health Interview Survey reported getting an average of 6 hours of sleep per day in 2005-2007. This new study suggests that even if we don't feel like we need more sleep, it's possible that getting less than 7 hours of sleep a night is negatively impacting our immune systems.
That means a significant number of us are ripe for getting sick. Only about 50% of how long we sleep is determined by our genes, so that really doesn't leave much of an excuse to try to modify the approximate 50% of the habits holding us back from getting a regular, good night's sleep.