Background The effect of passive smoking on the risk of coronary heart dise
ase is controversial. We conducted a meta-analysis of the risk of coronary
heart disease associated with passive smoking among nonsmokers.
Methods We searched the Medline and Dissertation Abstracts Online data base
s and reviewed citations in relevant articles to identify 18 epidemiologic
(10 cohort and 8 case-control) studies that met pre-stated inclusion criter
ia. Information on the designs of the studies, the characteristics of the s
tudy subjects, exposure and outcome measures, control for potential confoun
ding factors, and risk estimates was abstracted independently by three inve
stigators using a standardized protocol.
Results Overall, nonsmokers exposed to environmental smoke had a relative r
isk of coronary heart disease of 1.25 (95 percent confidence interval, 1.17
to 1.32) as compared with nonsmokers not exposed to smoke. Passive smoking
was consistently associated with an increased relative risk of coronary he
art disease in cohort studies (relative risk, 1.21; 95 percent confidence i
nterval, 1.14 to 1.30), in case-control studies (relative risk, 1.51; 95 pe
rcent confidence interval, 1.26 to 1.81), in men (relative risk, 1.22; 95 p
ercent confidence interval, 1.10 to 1.35), in women (relative risk, 1.24; 9
5 percent confidence interval, 1.15 to 1.34), and in those exposed to smoki
ng at home (relative risk, 1.17; 95 percent confidence interval, 1.11 to 1.
24) or in the workplace (relative risk, 1.11; 95 percent confidence interva
l, 1.00 to 1.23). A significant dose-response relation was identified, with
respective relative risks of 1.23 and 1.31 for nonsmokers who were exposed
to the smoke of 1 to 19 cigarettes per day and those who were exposed to t
he smoke of 20 or more cigarettes per day, as compared with nonsmokers not
exposed to smoke (P=0.006 for linear trend).
Conclusions Passive smoking is associated with a small increase in the risk
of coronary heart disease. Given the high prevalence of cigarette smoking,
the public health consequences of passive smoking with regard to coronary
heart disease may be important. (N Engl J Med 1999;340:920-6.) (C) 1999, Ma
ssachusetts Medical Society.