More than one in four adults ages 18 to 24 experience insomnia every night; it’s the highest rate of insomnia out of any age group in the U.S., according to a recent survey from Norwegian health and wellness publication Helsestart.

The company conducted a Google survey among 2,000 U.S. adults age 18 and up, asking respondents how often they struggle to fall asleep, as well as their genders and their ages.

Half of respondents said they experience insomnia at least once a month, while nearly a quarter said they struggle to fall asleep every night.

People often use the term “insomnia” in different ways, said Dr. Ronald Chervin, a neurology professor and division chief in the Sleep Disorders Centers at the University of Michigan who was not affiliated with the survey.

“When a lot of people talk about insomnia, they’re talking about the symptom; the symptom means having trouble falling asleep, having trouble with waking up during the night, having trouble going back to sleep if you wake up, or early morning awakenings,” he told USA TODAY.

Those experiences can be considered insomnia symptoms, but there are multiple disorders associated with sleep as well, including chronic insomnia and acute insomnia disorder.

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Martin Hareid, co-founder of Helsestart, said when the company began looking into insomnia for its survey, they saw many “outdated” publications that also focused on people already diagnosed with insomnia and receiving treatment.