Smoking and Psoriasis: Pack-years are linked to increased risk

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Researchers have found that smoking increases the risk of developing psoriasis, heavier smoking increases the risk further and the risk decreases only slowly after quitting. The study involved researchers from Boston at the Massachusetts General Hospital, Brigham and Women’s Hospital and the Harvard School of Public Health and researchers at Vancouver General Hospital. It was published in the November 2007 issue of The American Journal of Medicine.

Psoriasis is a noncontagious, lifelong skin disease that affects as many as 7.5 million Americans, according to the National Institutes of Health. About 10 percent to 30 percent of people with psoriasis also develop psoriatic arthritis, which causes pain, stiffness and swelling in and around the joints.

The study’s research team mined data collected in the Nurses Health Study II, an ongoing study of more than 116,0000 female registered nurses from 15 states between the ages of 25 and 42 who completed and returned an initial questionnaire in 1989. The researchers documented 887 incident cases of psoriasis during the 14 years of follow-up.

To quantify the extent of the smoking by the survey respondents, researchers measured lifetime smoking exposure in pack-years, equal to smoking 20 cigarettes per day for one year. Pack-years were associated with an increase in the risk for psoriasis. Compared with women who never smoked, the risk of psoriasis was 37 percent higher among past smokers and 78 percent higher among current smokers. Furthermore, the risk was 20 percent higher for those who had smoked between one and 10 pack-years, 60 percent higher for those who logged between 11 and 20 pack-years, and more than 200 percent higher for those who smoked for 21 or more years. Furthermore, exposure to passive smoke during pregnancy or childhood was associated with an increased risk of psoriasis.
There was good news for those who had quit smoking, though it wasn’t immediate. The risk of psoriasis among former smokers decreased to that of those who had never smoked 20 years after smokers had quit.