Passive smoking and the risk of hypertension in nonsmoking adults: a systematic review and meta-analysis

Background Previous studies on the association between passive smoking and hypertension are controversial. The association between these two elements remains inconclusive and requires a comprehensive meta-analysis. We conducted a systematic review and meta-analysis to explore this association. Methods We searched for full articles from four databases, including PubMed, Web of Science, Embase, and Cochrane databases, from 1971 until February 2025. Cross-sectional, case-control, and cohort studies examining the relationship between passive smoking exposure and the occurrence of hypertension were considered to be suitable for general analysis. Effect sizes and relevant 95% confidence intervals (CIs) were pooled and calculated. Results We included 13 studies, with 783,798 nonsmoking adults being included in the pooled analysis An association between passive smoking and elevated risk of hypertension was observed in cross-sectional/case-control studies (Effect size = 1.20, 95% CI [1.08–1.34], p = 0.001, I 2 = 99.1%) and in cohort studies (Effect size = 1.17, 95% CI [1.11–1.25], p < 0.001, I 2 = 0%). The result was still significant for cross-sectional/case-control studies after excluding two studies based on sensitivity analysis (Effect size =1.29, 95% CI [1.08–1.54], p = 0.005, I 2 = 73.5%). Subgroup analysis indicated that the increased risk was effective for both male and female populations. For the frequency and duration of secondhand smoking (SHS) exposure, only exposure ≥3 times/week (Effect size = 1.13, 95% CI [1.03–1.24], p = 0.012, I 2 = 64.8%) and ≥10 years (Effect size = 1.21, 95% CI [1.13–1.29], p < 0.001, I 2 = 0.0%) contributed to an increased risk of hypertension. Subgroup of hypertensive individuals defined by physical examination or self-reported diagnosis showed increased risk (Effect size = 1.15, 95% CI [1.09–1.22], p < 0.001, I 2 = 28.8%), but not for those defined by a structured questionnaire. Conclusion Exposure to passive smoking is significantly associated with an increased risk of hypertension in both cross-sectional/case-control and cohort studies, and for both male and female populations. Exposure ≥3 times/week and ≥10 years may have an adverse influence on hypertension.