Transgenerational consequences of grandparents' smoking on grandchildren's development: a systematic review.

OBJECTIVE: Research on the impact of smoking behaviour across generations has primarily focused on grandmaternal smoking during pregnancy. However, the broader multigenerational effects of smoking behaviour, notably through environmental and behavioural pathways, remain underexplored. This study evaluated previous studies on the possibility of transgenerational transmission, rather than in utero transmission, regarding the effects of grandparental smoking behaviour on offspring's development outcomes. DESIGN: This study is a systematic review with qualitative evidence synthesis. DATA SOURCES: A comprehensive search was conducted across multiple online databases, including PubMed, EBSCOhost, Web of Science and Scopus. To ensure a broad scope of relevant studies, publication dates, study locations and language were restricted to English only. STUDY SELECTION: After duplicates were removed, 3916 articles remained from the 4133 identified articles. Based on the predefined eligibility criteria, 38 articles were selected for full-text assessment. The selection process involved multiple reviewers, with disagreements resolved through consensus. DATA EXTRACTION: Multiple reviewers independently extracted data using a standardised protocol. The Joanna Briggs Institute critical appraisal tool was used to assess the quality of the included studies, with inter-rater reliability tests indicating moderate-to-high agreement. Extracted data included study design, participant demographics, exposure details and measured outcomes. DATA SYNTHESIS: This systematic review included seven studies because of heterogeneity in reported outcomes and effect measures. Three independent reviewers extracted data using a standardised coding sheet. The synthesis compared methodologies, identified gaps, key findings and conclusions across studies. RESULTS: Seven included articles examined grandchildren's behaviour, such as hyperactivity disorder, oppositional defiant disorder and conduct problems, body composition and IQ concerning grandparents' smoking habits. Most studies used robust statistical methods; two included parental factors as mediators. The synthesis of results indicated that the associations were primarily indirect. Key findings revealed that grandparents' smoking status was significantly associated with their grandchildren's physical and cognitive outcomes. Furthermore, the reviewed studies demonstrated sex-specific transgenerational effects of ancestral smoking on grandchildren's health, with stronger effects often observed in male descendants. CONCLUSIONS: This review highlights the methods and findings of previous studies on the potential transgenerational transmissions through which grandparents' smoking behaviour may influence grandchildren's behavioural, physical and cognitive development. Although the findings emphasise the importance of environmental and behavioural factors, further research is needed to address existing gaps and clarify mechanisms. PROTOCOL REGISTRATION: This systematic review protocol was registered in the PROSPERO database under registration number CRD42024571725.