The waterpipe smoking and human health: a systematic review and meta-analysis of 191 observational studies.

Background: While growing evidence highlights the harmful effects of waterpipe smoking (WPS), detailed information about its association to chronic diseases remains limited. This systematic review and meta-analysis exploring the association between WPS and various health conditions.

Methods: A systematic search of MEDLINE (via PubMed), Embase, Scopus, and Web of Science was conducted from inception to January 2025. Eligible observational studies on WPS and health outcomes were selected through a duplicate, independent process. Data extraction, including study details, participant characteristics, methods, and results, was performed independently by two reviewers using a standardized form. Methodological quality was assessed using the Newcastle-Ottawa scale (NOS), and studies were classified as high, moderate, or poor quality. The GRADE approach was applied to evaluate evidence certainty for each outcome, considering factors such as study design, risk of bias, consistency, precision, and publication bias.

Results: A total of 191 studies with 807,174 participants were included, comprising 98 case-control, 77 cross-sectional, and 16 cohort studies from 24 countries. The median number of studies analyzed per outcome was 5, with a range of 3 to 30. Among the 62 outcomes evaluated, 31 (50%) demonstrated statistically significant effect sizes based on a random-effects model, with stroke, coronary artery disease (CAD), and cancer mortality exhibiting a significant prediction interval. Credibility evaluations identified low-quality evidence for birth weight, CAD, and cardiovascular and cancer mortality, whereas the evidence for the remaining outcomes was graded as very low quality. Significant associations were found between WPS and several health outcomes: gastric cancer, lung cancer, bladder cancer, esophageal cancer, CAD, stroke, diabetes, metabolic syndrome, overall mortality, cardiovascular mortality, cancer mortality, infertility, sperm normal form, sperm DNA fragmentation, chronic bronchitis, cough, sputum, low birth weight (LBW), spirometry parameters, and several dental health indicators.

Conclusion: This study reveals strong links between WPS and adverse health outcomes, but low evidence quality calls for rigorous research and public health interventions to mitigate its effects.