A systematic review and meta‐analysis of environmental factors associated with juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIA) is the most common pediatric rheumatic disease, thought to be influenced by both genetics and the environment. Identifying environmental factors associated with disease risk will improve knowledge of disease mechanisms and ultimately benefit patients. This review aimed to collate and synthesize the current evidence of environmental factors associated with JIA.MEDLINE (Ovid), EMBASE (Ovid), Cumulative Index of Nursing and Related Health Literature (EBSCOhost), science network (WOS, Clarivate Analytics), Chinese National Knowledge Infrastructure, and Chinese Biological Medical Database were systematically searched. Study quality was rated using the Newcastle-Ottawa Scale. Pooled estimates for each environmental factor were generated using a random-effects, inverse-variance method, where possible. The remaining environmental factors were synthesized in narrative form.This review includes environmental factors from 23 studies (6 cohorts and 17 case-control studies). Cesarean section delivery was associated with increased JIA risk (pooled relative risk [RR] 1.103, 95% CI 1.033-1.177). Conversely, maternal smoking of more than 20 cigarettes/day (pooled RR 0.650, 95% CI 0.431-0.981) and gestational smoking (pooled RR0.634, 95% CI 0.452-0.890) were associated with decreased JIA risk.This review identifies several environmental factors associated with JIA and demonstrates the huge breadth of environmental research. We also highlight the challenges of combining data collected over this period due to limited study comparability, evolution in healthcare and social practices, and changing environment, which warrant consideration when planning future studies.