ABSTRACT

Data on never-smoking decedents from 1986 National Mortality follow-back Survey were used to perform a case-control analysis of ischemic heart disease in relation to spousal cigarette smoking. The case group consisted of 475 men and 914 women who dies from heart disease. Controls consisted of 998 men and 1930 women who died from other causes. In this study there was no association between spousal smoking and ischemic heart disease in either sex (males, odd ratio = 0.97; females, odd ratio = 0.99) The results of this study are in striking disagreement with risk elevations reported in several previous studies of spousal smoking and heart disease.

INTRODUCTION

Several epidemiologic studies have reported associations between ischemic heart disease mortality in never-smokers and exposure to environmental tobacco smoke (ETS) from spousal smoking (Hirayama, 1984; Garland et al., 1985; Lee et al., 1986; Martin et al., 1986; Svendsen et al., 1987; Butler, 1988; Helsing et al., 1988; Palmer et al., 1988; He, 1988; Hole et al., 1989; Jackson, 1989; Humble et al., 1990; Dobson et al., 1991; La Vecchia et al., 1994)Despite the high rate of heart disease death among never-smokers, most of the studies have included relatively few cases; only threes studies (Hyrama, 1984; Helsing et al., 1988; Dobson et al., 1991) included substantially more than 100 cases. Although some review panels concluded that there was insufficient evidence to infer that ETS exposure increases the risk of heart disease (National Research Council, 1986; U.S. Surgeon General, 1986), other reviews have drawn such an inference (Wells, 1988; Glantz and Parmley, 1991; Steenland, 1992; Taylor et al., 1992).

The National Mortality Follow-back Survet (NMFS), which was based on a probability sample of adult deaths in the United States in 1986, offered the opportunity to perform a case-control analysis of ischemic heart disease and spousal smoking cases than any previously published study. This paper reports the results of the case-control study.

MATERIALS AND METHODS

The National Mortality Follow-back Survey was conducted in 1986 by the US National Center for Health Statistics (NCHS) (NCHS, 1988; Seeman et al., 1989). The survey was bases on a national probability sample of about 1% of all deaths in 1986 in the U.S. residents aged 25 years or older. This sample was drawn from the Current Mortality Sample (CMS), a 19% sample of death certificates that NCHS receives from state authorities approximately 3 months after the deaths occur. The NMFS sample included data fom 49 states and the District of Columbia; deaths from Oregon were not included because of respondent consent requirements.

Of the 18,733 death certificates in the NMFS sample, about 2,500 were selected with certainty from the CMS for certain causes of death and population subgroups. These included all deaths due to ischemic heart disease (Internal Classification of Diseases, Revision 9, codes 410-414) for males aged 25-44 years and for females aged 25-54 years. In addition, some population groups were over-sampled. For example, black decedents were over-sampled 2.9 times and those under 55 years were over-sampled 3.1 times.

Next of kin of decedents in the NMFS sample were asked to complete a questionnaire that included questions on demographic characteristrics, dietary patters, cigarette smoking (personal and spousal), alcohol consumption, education, income, and history of disease. The questionnaire response was 88.6%. The NMFS is described in more detail in Seeman et al., 1989).

The decedents included in the present study were restricted to those reported by next of kin to be lifetime never-smokers, defined to be those who had never smoked 100 or more cigarettes in their entire lives. Furthermore, decedents were excluded from analysis if they had never married or their marital status was unknown or if it was not known whether their spouse had smoked; 549 male and 692 female subjects were excluded for these reasons.

After these exclusions, the case group consisted of 1,389 (475 male and 914 female) ischemic heart disease deaths. Deaths from causes generally considered to be smoking related were excluded from the control group. Deaths from causes generally considered to be smoking related were excluded from the control group. Excluded causes of deaths were cancers of the lung, mouth, pharynx, larynx, oesophagus, pancreas, bladder, kidney and cervix, cerebrovascular disease, and chronic obstructive lung disease. The control group then consisted of 998 male decedents and 1930 female decedents.

Spousal smoking status was based on answers to two questions asked of questionnaire respondents about the decedents: "Did (any) spouse smoke at least 100 cigarettes?"; and "How many cigarettes a day did (this) spouse smoke?" (If more than one spouse smoked, the answer to the second question was for the most recent spouse.)

Multiple logistic regression methods were used to estimate spousal smoking odds ratios adjusted for age and race (Breslow and Day, 1980). Trend tests were calculated by assigning scores to exposure category, and adding the quantitative variable so defined to the logistic regression model.

RESULTS

[...]

No overall spousal smoking-heart disease risk elevation was observed for either males or females, the adjusted odds ratios being 0.97 and 0.99 respectively (Table 2), nor was there for either sex any significant trend in risk with increasing numbers of cigarettes smoked per day by the spouse (trend test P values: males: 0.8; females: 0.3).

The spousal smoking results were not appreciably affected by adjustment for history of hypertension, history of diabetes, family history of heart attack, relative weight, alcohol consumption, dietary factors, education, and family income. There was no significant age-spousal smoking interactions.

DISCUSSION AND CONCLUSIONS

In this study there was no suggestion of an association between exposure to ETS from spousal smoking and ischemic heart disease. Odds were below 1.0 for both men (odds ratio=0.99), and there was no indication of an increasing trend in risk with increasing numbers of cigarettes smoked by the spouse.

[...]

The results of the present study are in marked contrast to risk elevations reported in other ETS- heart disease epidemiologic studies...

[...]

The results of this study are consistent with those of recent analyses of data no spousal smoking and heart disease from two large American Cancer Society cohort studies.. [...]. Neither of those analyses suggested an association between spousal smoking and heart disease.

[...]

... the ETS-heart disease epidemiology clearly does not justify an inference that ETS exposure increases heart disease risk, and estimates of never-smoker heart disease deaths attributable to ETS exposure are without a valid basis.