If you’re a morning person, you may have a reduced risk of major depression, a new study suggests.
Several studies of the body’s circadian sleep-wake cycle have shown that being an early riser is associated with a lower risk of depression. But these studies were observational and therefore could not prove cause and effect.
For example, people who are early risers may have other health or lifestyle behaviors that lower their risk of depression – they may eat healthier foods, for example, exercise more or have fewer problems with depression. health, such as chronic pain, which are associated with depression. All of these factors, and many more, could explain the decreased risk of depression, not being an early riser. Additionally, depression itself causes trouble sleeping, so it could be that depression is a cause of being a night owl, rather than the other way around.
The new study, however, offers more compelling evidence that going to bed early and waking up early may, in and of itself, offer protection against depression, independent of other factors. The study, published in JAMA Psychiatry, uses a research method called Mendelian randomization that helps identify the cause of what may be a cause-and-effect relationship.
With Mendelian randomization, researchers can compare large groups of people based on genetic variants independent of other health or behavioral characteristics – in this case, the tendency to be a night owl or a morning person. inherited traits that are randomly assigned during our development. in the womb. Over 340 genetic variants associated with the circadian sleep rhythm have been identified, and researchers can compare large groups of people with the genetic variants to be a morning person with groups lacking. Nature has, in essence, set up the randomized experiment for them.
For the study, scientists used two genetic databases of more than 800,000 adults to perform a Mendelian randomization study of circadian rhythm and risk of depression. They had not only genetic data, but also data on major depression diagnoses and information on when people went to bed and woke up, collected with both self-reports and sleep lab records. , which the researchers used to track the sleep midpoint, a useful scientific measure of someone’s sleep patterns. A morning person who tended to go to bed at 10 a.m. and wake up at 6 a.m., for example, would have median sleep at 2 a.m.
They found that in people with the genetic variants to be an early riser, for every hour before the midpoint of sleep, there was a 23% lower risk of major depression.
Dr Till Roenneberg, an expert in chronobiology who was not involved in the research, said that one gap in the study was that scientists had no data on when these people should get up to work or for other obligations. Even with Mendelian randomization, he says, they can’t explain the fact that late types often have to go to work too early, which in itself can contribute to depression.
“They drew the right conclusions from their data,” he said, “but life is more complicated than that.”
If you are a night owl, will changing your habits relieve depression or lower your risk of developing it? Not necessarily, said lead author Dr. Iyas Daghlas, resident physician at the University of California, San Francisco. The study, he said, looks at large groups of people, not individuals.
“These data tell us that certain trends in society” – such as the use of smartphones and other blue light devices at night, which make us fall asleep later – “may have an effect on the level of depression of the population, “he said. . “These results don’t say that if you fall asleep earlier, you’ll get rid of depression. Finding out which intervention in which populations will be effective – this should be left to clinical trials. “
Still, he said, “While our data doesn’t tell us where the sweet spot is, I would say if you’re an evening person, especially someone who has to get up early, bring your bedtime forward by about one hour. hour is a safe intervention that could be helpful for your mental health.