If you're a morning person, you may have a lower risk of major depression, a new study suggests.
Several studies of the body's circadian sleep-wake cycle have shown that getting up early is associated with a lower risk of depression. But these studies were observational, so cause and effect could not be established.
For example, people who are early risers may have other health or lifestyle habits that reduce their risk of depression – such as eating healthier diets, exercising more, or having fewer health problems such as chronic pain associated with depression. All of these factors and many others could explain your lower risk for depression rather than being an early bird. Furthermore, depression itself causes insomnia, so depression could be a cause of being a night owl rather than the other way around.
However, the new study provides more compelling evidence that going to bed and waking early can in itself provide protection against depression, regardless of other factors. The study, published in JAMA Psychiatry, uses a research method called Mendelian randomization, which helps pinpoint the cause of a possible cause-and-effect relationship.
Mendelian randomization allows researchers to compare large groups of people based on genetic variants that are independent of other health or behavioral traits – in this case, tendency to be a night owl or morning person, inherited traits that are randomly assigned during our development in the womb. More than 340 genetic variants associated with circadian sleep rhythms have been identified, and researchers can compare large groups of people with a morning person's genetic variants to groups lacking them. Nature essentially set up the randomized experiment for them.
For the study, the scientists used two genetic databases from more than 800,000 adults to conduct a Mendelian randomization study of circadian rhythm and the risk of depression. In addition to genetic data, they also had data on major depressive disorder diagnoses and bedtime and wake information collected with both self-reports and sleep laboratory records that researchers used to track mid-sleep, a helpful scientific measure of a person's sleeping tendencies . For example, a morning person who tends to go to bed at 10 and wake up at 6 will have a mid-sleep point of 2 a.m.
They found that people with the early riser genetic variants had a 23 percent lower risk of major depression for every hour before mid-sleep.
Dr. Till Roenneberg, a chronobiology expert who was not involved in the research, said one shortcoming of the study was that the scientists didn't have data on when these people had to get up for work or other duties. Even with Mendelian randomization, he said, they can't explain that late guys often have to get to work early. which in itself can contribute to depression.
"You have drawn the right conclusions from your data," he said, "but life is more complicated."
If you are a night owl, will changing your habits relieve depression or reduce your risk of developing it? Not necessarily, said lead author Dr. Iyas Daghlas, a resident doctor at the University of California at San Francisco. The study, he said, looked at large groups of people, not individuals.
"These data show us that certain trends in society" – such as the nightly use of smartphones and other blue-light devices that make us fall asleep later – "may have an impact on the severity of depression in the population," he said. “These results don't say that going to sleep earlier will get rid of depression. Finding out which intervention is effective in which populations – that has to be left to clinical studies. "
Nonetheless, he said, “Although our data doesn't tell us where the sweet spot is, I would say that if you are a night owl, especially when you have to get up early, bringing your bedtime about an hour forward is a safe intervention that is good for your mental health Health could be helpful. "