If you are a morning person, you may be at reduced risk for
major
depression, a new study suggests.
اضافة اعلان
Several studies of the body’s circadian sleep-wake cycle have
shown that being an early bird is associated with a lower risk for depression.
But those studies were observational so could not prove cause and effect.
For example, people who are early birds may have other
health or
lifestyle behaviors that reduce their risk for depression — they may have a
healthier diet, for example, exercise more or have fewer health conditions,
such as chronic pain, that are associated with depression. All these factors,
and many others, could explain the decreased risk for depression, and not the
fact of being an early bird. Moreover, depression itself causes sleep
disturbances, 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 early may, in itself, provide protection against
depression, independent of other factors. The study, published in
JAMAPsychiatry, uses a research method called Mendelian randomization that helps
pinpoint 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 that are independent of other health
or behavioral characteristics — in this case, the tendency to being a night owl
or a morning person, inherited traits that are randomly allocated during our
development in the womb. More than 340 genetic variants associated with
circadian sleep rhythm have been identified, and the researchers can compare
large groups of people with the genetic variants for being a morning person
with groups that lack them. Nature has, in essence, set up the randomized
experiment for them.
For the study, the scientists used two genetic databases of more
than 800,000 adults to do a Mendelian randomization study of circadian rhythm
and the risk for depression. They not only had genetic data, but also data on
diagnoses of major depression and information on when people went to bed and
woke up, collected with both self-reports and sleep laboratory records, which
the researchers used to track the midpoint of sleep, a helpful scientific
measure of someone’s sleep tendencies. A morning person who tended to go to bed
at 10 and wake up at 6, for example, would have a sleep midpoint of 2 am.
They found that in people with the genetic variants for being an
early bird, for every hour earlier the sleep midpoint, there was a 23 percent
lower risk of major depression.
Dr. Till Roenneberg, an expert in chronobiology who was not
involved in the research, said a shortcoming of the study was that the
scientists had no data on when these people had to rise for work or other
obligations. Even with Mendelian randomization, he said, they cannot account
for the fact that late types often need to go to work too early, which in itself
may contribute to depression.
“They’ve drawn 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 alleviate
depression or decrease the risk for developing it? Not necessarily, said the
lead author, Dr. Iyas Daghlas, a resident physician at the University of
California, San Francisco. The study, he said, looks at large groups of people,
not individuals.
“This data tells us that certain trends in society” — such as using
smartphones and other blue light devices at night, which make us go to sleep
later — “may be having an effect on the level of depression in the population,”
he said. “These results do not say that if you go to sleep earlier, you’ll get
rid of depression. Discovering which intervention in which populations will be
effective — that has to be left to clinical trials.”
Still, he said, “While our data doesn’t tell us where the sweet
spot is, I would say that if you’re an evening person, especially one who has
to wake up early, advancing your bedtime about an hour or so is a safe
intervention that might be helpful for your mental health.”
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