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Still, there is little evidence to suggest that marijuana use actually results in sleep improvements. "There's a lot of research on sleep and cannabis, but it's a little mixed," explained study co-author Evan Winiger, a graduate student in behavioral genetics, psychology and neuroscience at the University of Colorado, in Boulder.
In the study, Winiger and his colleagues analyzed the sleep habits and history of marijuana use among 1,882 teens from Colorado. To get at the potential genetic components of marijuana use and sleep disturbances, all of the participants were twins.
The results showed that roughly one-third of the participants who started using marijuana before age 18 had insomnia later in life. Only 20% of the other participants -- who either never became regular marijuana users or started their use at age 18 or older -- had insomnia in adulthood.
The teenage marijuana users were also more likely to experience a particularly detrimental type of sleep called "short sleep," or sleeping less than six hours per night. Short sleep is associated with various chronic health issues, including heart disease, asthma and arthritis, according to the U.S. Centers for Disease Control and Prevention.
Ten percent of those who regularly used marijuana in their teenage years said they were short sleepers in adulthood, compared to only 5% of those who never used, the findings showed.
There are a few theories as to why marijuana may affect sleep, but no absolute answers. The primary view, according to sleep experts, is that marijuana influences your circadian rhythm, the system that tells the body when to sleep and when to wake up.
Since the study participants were twins -- some identical and some fraternal -- the authors were able to tease out whether the associations between marijuana use and sleep problems were genetic.
The investigators identified that some of the same genes that influenced whether people started using marijuana early in their life also played a role in the likelihood of later sleep problems.
The study was the first to identify such a link, according to Winiger. "There's not a lot of research on the overlapping genetics between these domains," he said.
The findings were published recently in the journal Sleep.
The limitations of the study, some acknowledged by the authors and others not, include the fact that the results were based on self-reported information, which could be prone to bias and memory errors, according to Bhanuprakash Kolla, a psychiatrist and neurologist at the Mayo Clinic in Rochester, Minn.
In addition to the self-reporting bias, Kolla noted that "the authors did not account for the possible use of other substances, such as tobacco and alcohol, which can also influence sleep."
Winiger and his team did account for some possibly contradicting variables, such as prior diagnoses of depression or anxiety. They adjusted the results to control for those variables, as depression and anxiety disorders are known to have an effect on sleep.
Dr. Nathaniel Watson, a former president of the American Academy of Sleep Medicine and a professor of neurology at the University of Washington, thinks that the full story of marijuana and sleep has not yet been told.
Watson said that widespread legalization of marijuana will allow researchers to study it in more controlled environments, like a clinical trial. He thinks that future studies may show that marijuana does have some potential benefits for sleep, but there is not enough evidence to come to a conclusion either way.
"Nonetheless, this is an impressive study," Watson said. "It adds to our growing understanding of the relationship between cannabis and sleep."
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