Insomnia costs Quebec about $6.5 billion a year, mostly through lost productivity among those who can't sleep, according to a new study.

The figures calculated by researchers from the University of Laval in Quebec City suggest "the economic burden of untreated insomnia is much higher than that of treating insomnia," so there should be more studies of therapies.

The condition costs insomniacs $5,010 each, while people with symptoms lose $1,431. But insomnia even costs good sleepers $421 each, according to an abstract of the article published Thursday in the journal Sleep.

Insomnia is "highly prevalent " and entails both direct costs through the increased use of health-care services and products, and indirect costs in terms of lost productivity and absenteeism.

The indirect costs accounted for most of the total, with annual productivity losses pegged at $5 billion and absenteeism at $970.6 million.

Direct costs, such as for health care, and prescription and over-the-counter medications, account for the rest, about $586 million. But the biggest single indirect cost, at $339.8 million, was alcohol used as a sleep aid, the authors said.

The study was based on questionnaires on sleep, health, use of health-care services and products, accidents, work absences and productivity distributed to a random sample of 948 Quebec adults.

"Participants were categorized as having insomnia syndrome, insomnia symptoms or as being good sleepers using a standard algorithm," the abstract said.

Quebec government medial data were also used.

The authors are Meagan Daley, Charles M. Morin, Mélanie LeBlanc, Jean-Pierre Grégoire and Josée Savard.