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Those early birds may think they’re morally superior, but a new study supports the idea that how long you sleep may be encoded in your DNA.

Researchers looked at the DNA of more than 50,000 people taking part in a variety of health studies who had all reported how much sleep they get every night. They found that people who habitually undersleep or oversleep have mutations in their DNA that may be associated with thyroid hormones.

The mutations were in an area of the genome that may control a gene called PAX8 that’s associated with thyroid development. Doctors know that people with overactive thyroids often suffer from insomnia, while underactive thyroid function can make people sleepy or sluggish. In this case, the associations were not quite so clear-cut and now it’ll be up to researchers to see how the mutation may or may not affect people’s thyroids.

“These findings suggest a role for thyroid hormone in sleep–wake regulation and thus a plausible role for PAX8 effects on sleep duration,” Dr. Daniel Gottlieb of the VA Boston Healthcare System and Brigham & Women’s Hospital and colleagues wrote in the journal Nature Molecular Psychiatry.

It’s more than just academic. Too much or too little sleep are associated with mental illness, high blood pressure, diabetes and other diseases.


-- Maggie Fox