4. Discussion
This meta-analysis is the most comprehensive study that evaluated
the effect of SHS exposure on all-cause mortality and CVD. The number
of studies included in our analysis was almost doubled compared with
that of previous ones [2–4]. Our analysis indicated that never smokers
exposed to SHS, comparedwith those unexposed, had a significantly increased
risk of 18% for all-cause mortality, 23% for CVD, 23% for CHD,
and 29% for stroke. Various study characteristics, such as gender and
age distribution, source of exposure, study design, and follow-up duration,
did not seemto influence the results. Nonetheless, a stronger association
was observed among studies in China than those in Europe and
the US. Moreover, the objectively measured SHS exposure might be associated
with a higher risk for CVD in comparison with self-reported
SHS exposure.