The link between sleep and health has never been stronger, but for all the data that chides us for not getting enough rest each night, there are still lingering questions. For instance, how is it possible that sleep can be linked to seemingly unrelated health effects, including cardiovascular disease and anxiety? Well, at least when it comes to heart disease, a new paper in Experimental Physiology provides some concrete answers.
Lack of sleep can affect mood and academic performance, but it has also been linked to heart conditions in population-based studies. The CDC has published materials suggesting that sleeping for less than seven hours is linked to type 2 diabetes, obesity, and high blood pressure, all of which increase the risk of heart disease.
Working with Jamie Hijmans, a doctoral candidate and fellow in DeSouza’s lab, the team showed that sleeping for less than seven hours a night can reduce specific fragments of non-coding RNA molecules found in blood called microRNAs.
“Circulating levels of specific microRNAs, such as the ones we studied, have been linked to cardiovascular health and disease,” Hijmans tells Inverse. “For example, reduced levels of a beneficial microRNA can have adverse consequences.”
Lack of sleep, it seems, can reduce levels of these “beneficial microRNAs,” which DeSouza and Hijmans showed on a a small sample of 24 middle-aged adults.
Participants reported how many hours they slept per night, and the researchers divided them into two even groups: those who reported sleeping for seven hours or more, and those who slept for less than seven hours.
That seven-hour mark isn’t a hard and fast benchmark for a healthy amount of sleep. Usually the range is somewhere from seven to nine hours of sleep — though seven seems to consistently be on the low end of the healthy range and is used in the CDC’s guidance materials. However, there are subgroups, like teens, which may require far more sleep to function normally. As far as microRNAs go, seven seems to work as a benchmark, adds Hijmans.
“Epidemiological data indicates that people who habitually sleep between seven and nine hours a night are at significantly lower risk of developing heart disease than those who habitually sleep less than seven hours per night,” he says. “Why seven or eight hours seems to be the ‘magic’ number is unclear. However, it is plausible that people need at least seven hours of sleep per night to maintain levels of important physiological regulators, such as microRNAs.”
Importantly, differences in sleep time showed effects on the microRNAs circulating in the blood of people in each group. The short sleepers tended to have fewer levels of specific microRNAs that have demonstrated effects on heart health. For example, short sleepers had lower levels of miR-146a, which Hijmans says “has been shown to suppress cardiovascular inflammation.”
“A reduction of the circulating levels of miR-146a has been shown to result in greater levels of vascular inflammation, an important precursor to heart disease,” he adds.
This study offers interesting insight into how sleep affects the body, but it does have some important caveats. For instance, it’s possible that these changes in microRNA could come down to diet or other lifestyle factors, though the researchers tried to ensure that the subjects all had relatively similar levels of fitness or body composition.
"We are currently studying this exact question."
Overall, Hijmans says that this study is proposing a new way to look at sleep’s effects on heart health, adding that “these findings offer a potential road map for future studies.” There’s really a lot more to learn, including whether actually getting more than seven hours of sleep each night might help to restore those levels of microRNAs. “We are currently studying this exact question,” says Hijmans, but as it stands, it seems plausible that getting more sleep will have that restorative effect.
“We would expect that increasing nightly sleep duration would beneficially affect the circulating microRNA profile,” he adds.
It may be too early to write a prescrption for sleep to help improve these tiny molecular markers of heart health, but this study shows they’re something to watch.
Abstract: Habitual short sleep duration (<7 h night−1) is associated with increased morbidity and mortality attributable, in large part, to increased inflammatory burden and endothelial dysfunction. MicroRNAs (miRNAs) play a key role in regulating vascular health, and circulating levels are now recognized to be sensitive and specific biomarkers of cardiovascular function, inflammation and disease. The aim of this study was to determine whether the expression of circulating miR‐34a, miR‐92a, miR‐125a, miR‐126, miR‐145, miR‐146a and miR‐150 is disrupted in adults who habitually sleep <7 h night−1 (short sleep). These were chosen based upon their well‐established links with vascular inflammation, function and, in turn, cardiovascular risk. Twenty‐four adults were studied: 12 with normal nightly sleep duration (six men and six women; age, 55 ± 3 years old; sleep duration, ≥7.0 h night−1) and 12 with short nightly sleep duration (seven men and five women; 55 ± 2 years old; sleep duration, <7 h night−1), and circulating miRNA expression was assayed by RT‐PCR. All subjects were non‐smokers, normolipidaemic, non‐medicated and free of overt cardiovascular disease. Circulating levels of miR‐125a (3.07 ± 1.98 versus 7.34 ± 5.34 a.u.), miR‐126 [1.28 (0.42–2.51) versus 1.78 (1.29–4.80) a.u.] and miR‐146a [2.55 (1.00–4.80) versus 6.46 (1.50–11.44) a.u.] were significantly lower (∼60, 40 and 60%, respectively) in the short compared with the normal sleep group. However, there were no significant group differences in circulating levels of miR‐34a, miR‐92a, miR‐145 and miR‐150. In summary, chronic short sleep is associated with a marked reduction in circulating levels of miR‐125a, miR‐126 and miR‐146a. Dysregulation of these miRNAs might contribute to the increased inflammatory burden and endothelial dysfunction associated with habitual insufficient sleep.