Most subjects with ETS data were non-Hispanic white (91% cases, 93% controls), male (66% cases, 69% controls), and born before 1950 (84% cases, 92% controls). All cases were diagnosed in 2002–2008, most (71%) at age 60 years or older (median 66 years). Age at reference was ≥ 60 years for 77% of controls (median 70 years). Most Group Health Cooperative participants (69% cases, all controls) had been enrolled for ≥ 10 years (90% cases, 88% controls). Fifty-one percent of cases and 59% of controls had ever been active tobacco smokers. College degrees (53% cases, 49% controls), daily caffeinated coffee consumption (67% cases, 69% controls) and any regular alcohol consumption (58% cases, 65% controls) were common. Relatively few participants had a first-degree relative with PD (9 cases, 5 controls), had never been married (9 cases, 5 controls), or had never worked outside the home (1 case, 1 control).
Compared with those who had never been active or passive smokers, we observed a similarly reduced PD risk for only ever having been exposed to ETS (OR=0.34, 95% CI 0.16–0.73, ) as for ever active smoking (OR=0.35, 95% CI 0.17–0.73, ). When we compared those who both actively and passively smoked to those who only actively smoked, no inverse association between PD and passive smoking was noted (OR=1.57, 95% CI 0.62–3.96, footnote), in contrast (interaction p-value=0.01) to the strong inverse PD-passive smoking association noted above among never active smokers. These associations were similar among men and women (), and whether ETS exposure occurred at home or work (). Results were unaltered when we either excluded cases ascertained outside of Group Health Cooperative, or adjusted for education, birth year and typical consumption of alcohol and caffeinated coffee (both passive and active smoking ORs 0.33–0.36, both interaction p-values 0.01–0.02, data not shown in tables).
Risk of Parkinson disease and active and passive tobacco smoking,a overall and by sex, western Washington, 2002–2008
Risk of Parkinson disease and active and passive tobacco smoking,a by passive smoking location, western Washington, 2002–2008
When we considered the number of active smokers at home or at work, and the number of years ETS-exposed at each location, a dose-related reduced PD risk was not evident, with one exception that was based on only 18 cases and 25 controls. Among individuals only exposed to tobacco smoke through passive smoking at home, PD risk was inversely related to the number of years living with a daily smoker (OR=0.86, 95% CI 0.75–0.99 per year). Ten (56%) cases and 5 (20%) controls (Fisher’s exact p=0.02) lived with a daily smoker for <18 years, the mode for cases and controls.