Cigarette Smoking Among Spouses
Another Risk Factor for Stroke in Women
Background and Purpose— It is well known that passive exposure to cigarette smoking increases the risk of coronary events, but the effect on the risk of stroke is not well defined. We performed this study to determine the effect of cigarette smoking among spouses on the risk of developing stroke and ischemic stroke among a nationally representative sample of women.
Methods— We examined the association between history of smoking among spouses with the incidence of stroke in a national cohort of 5379 women who participated in the First National Health and Nutrition Examination Survey Epidemiologic Follow-Up Study.
Results— During a mean follow-up of 8.5 years, the risk was significantly increased for all strokes (relative risk, 5.7; 95% CI, 1.4 to 24) and ischemic stroke (relative risk, 4.8; 95% CI, 1.2 to 20) among cigarette-smoking women with a cigarette-smoking spouse compared with those with a nonsmoking spouse after adjusting for other cardiovascular risk factors.
Conclusion— The study provides new evidence linking spousal smoking to stroke.
It is well known that passive exposure to cigarette smoking increases the risk of coronary events,1 but the effect on the risk of stroke is not well defined. We performed this study to determine the effect of cigarette smoking among spouses on the risk of developing stroke and ischemic stroke among a nationally representative sample of women.
We used the data from 12 220 participants aged 25 to 74 years evaluated from 1982 to 1984 as part of the First National Health and Nutrition Examination Survey Epidemiologic Follow-Up Study (NHEFS).2 Of the 12 220 participants, 7279 were women. Subsequently, 1900 were excluded from the analysis because of previous cardiovascular diseases (n=712), missing follow-up (n=572), spouse smoking status unknown (n=72), missing values for cholesterol, diabetes mellitus, blood pressure, or body mass index (n=405), and missing values for smoking duration (n=139). In the 1982 to 1984 visit, several questions were inquired, including whether the participant was actively smoking, daily cigarette consumption, years of cigarette smoking, and active cigarette smoking among spouses. We defined incident all stroke cases as study participants who were hospitalized or died during the 10-year follow-up period with International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes 431 to 434.9 or 436 to 437.1. The strokes were further categorized as ischemic stroke (ICD-9-CM codes 433 to 434.9 or 436 to 437.1) and intracerebral hemorrhage (ICD-9-CM codes 431 to 432). Cardiovascular disease was defined by either stroke or coronary artery disease (ICD-9-CM codes 410 to 414). The definitions of stroke and cardiovascular diseases were consistent with previous reports.3,4 Potential confounders in the association in the analyses were age, race/ethnicity (black, white, other), systolic blood pressure, hyperlipidemia (serum cholesterol <200 or ≥200 mg/dL), obesity (body mass index≥30.0 kg/m2), diabetes mellitus, cigarette smoking (former, current), average daily cigarette consumption, alcohol consumption (never, moderate, and heavy) and duration of smoking. All measures were obtained prospectively during the National Health and Nutrition Examination Survey I, 1982 to 1984 visit, except serum cholesterol measurements, which were obtained from baseline interview. Cox proportional hazards analysis was used to estimate the relative risk (RR) for stroke and cardiovascular diseases. Because of significant interaction between smoking status of participant and spouse, the analysis was performed in cigarette-smoking and nonsmoking women separately. Annual household income inquired from 2172 of the 2347 cigarette-smoking and 2759 of 3032 nonsmoking women was entered as provided in original dataset (<3000; 3000 to 3999; 4000 to 4999; 5000 to 5999; 6000 to 6999; 7000 to 9999; 10 000 to 14 999; 15 000 to 19 999; 20 000 to 24 999; 25 000 to 34 999; 35 000 to 49 999; 50 000 to 74 999; 75 000 to 100 000; >100 000; and missing).
Of the 5379 women included in the analysis, women who reported a cigarette-smoking spouse (n=3727) were more likely to be active smokers and reported higher cigarette consumption and years of smoking (Table 1). The mean follow-up duration (years ±SD) was 8.5±2.1. The risk of all strokes (RR, 5.7; 95% CI, 1.4 to 24) and ischemic stroke (RR, 4.8; 95% CI, 1.2 to 20) was increased among cigarette-smoking women with a cigarette-smoking spouse compared with women with nonsmoking spouses after adjusting for differences in potential confounders (Table 2). The increased risk of all strokes (RR, 5.8; 95% CI, 1.4 to 24) and ischemic stroke (RR, 4.8; 95% CI, 1.2 to 20) persisted after adjustment for annual household income. No association between cigarette smoking in spouses and risk of all strokes or ischemic stroke was identified among nonsmoking women (Table 3).
The present results are derived from a nationally representative probability sample of the US civilian noninstitutionalized population and potentially lack the biases observed with longitudinal studies conducted on selected population samples. Previous studies5,6 have reported an increased risk for either all stroke or ischemic stroke among active smokers exposed to environmental tobacco smoke5 or spousal smoking.6 Both studies also reported an increased risk for nonsmoking participants, unlike our study. However the relationship has not been consistently observed in longitudinal studies.7 Whether this difference is related to the different design (case control versus cohort) or lack of adjustment for potential confounders such as serum cholesterol and body mass index in previous studies is unclear. The possibility that spouses of nonsmoking women may be more likely to quit or reduce cigarette smoking during the follow-up period cannot be excluded. Smoke exposure may also be lower in nonsmoking women because spouses may avoid smoking in close proximity. Some limitations of the analyses need to be considered. Because of the small number of events observed, potential relationships such as those between spousal smoking and cardiovascular diseases may be underestimated. Some variables such as dietary intake were not available in 1982 to 1984 interviews and could not be adjusted for in the model.
Our prospective cohort study suggests that spousal cigarette smoking may be associated with all strokes and particularly ischemic stroke among women.
- Received September 3, 2004.
- Revision received February 24, 2005.
- Accepted March 3, 2005.
Engel A, Murphy RS, Maurer K, Collins E. Plan and operation of the HANES I augmentation survey of adults 25–74 years United States, 1974–1975. Vital Health Stat 1. 1978; 14: 1–110.
Bonita R, Duncan J, Truelsen T, Jackson RT, Beaglehole R. Passive smoking as well as active smoking increases the risk of acute stroke. Tob Control. 1999; 8: 156–160.