Published in The Lancet Psychiatry, the study analyzed 91,000 United Kingdom residents aged 37 to 73 who wore an accelerometer on their wrist for one week. Researchers determined the circadian rhythmicity of the subjects' rest-activity cycles—AKA, how consistent they are about bedtime and wake-up time—a measure dubbed the "relative amplitude variable." They then examined the connection between a low relative amplitude variable (a regularly disrupted circadian rhythm) and conditions such as depression, happiness, and cognitive functioning (using a model that accounted for demographics, lifestyle, education, and other factors that might influence these conditions).
The study found an association between a disrupted sleep routine and an increased risk of major depressive disorder and bipolar disorder, more subjective loneliness, and lower happiness and health satisfaction.
The results showed an association between a low relative amplitude and an increased risk of major depressive disorder and bipolar disorder, more subjective loneliness, and lower happiness and health satisfaction. In other words, if your bedtime changes drastically from day to day, you're likely to experience poor mental health.
“We found that people who tended to have lower relative amplitude, indicating that they’ve got less marked distinction between their rest and activity periods, were more likely to meet the criteria for lifetime depression and bipolar disorder,” lead study author Laura Lyall, PhD, said in a podcast related to the study.
However, the study was not able to prove causality, so it's possible that poor mental health leads to a tumultuous circadian rhythm rather than vice versa. Still, considering the study's strong correlation between sleep quality and mental health—causal or not—it should be evidence enough to prioritize consistent shut-eye. After all, making sure your busy work week is accompanied by some sort of structured sleep schedule is vital for functioning at your best. You don't want to show up to work the next morning feeling as though you're drunk, right?
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