Washington, Sep 10 - Depressed and anxious people are among the heaviest smokers, but doctors seldom insist that they quit, fearing their mental disorders will get out of hand. A researcher has, however, questioned this theory.

That is a myth, says Brian Hitsman, tobacco addiction specialist and assistant professor of preventive medicine at Northwestern University Feinberg School of Medicine.

Hitsman has designed and published the first comprehensive, evidence-based plan for psychiatrists, psychologists and others to help their patients quit smoking.

'These doctors and mental health specialists focus on their patients' psychiatric health and lose track of their physical health,' said Hitsman, who is also a health psychologist.

Between 40 to 80 percent of the mentally ill are daily smokers, depending on the disorder, compared to less than 20 percent of those considered normal, say researchers.