The effect of day care exposure on the risk of developing type I diabetes - A meta-analysis of case-control studies

OBJECTIVE - Exposure to infections in infancy or childhood may be important in the pathogenesis of type 1 diabetes, but a protective role has also bee n suggested. We tested the hypothesis that increased early contact with inf ectious agents, measured by day care exposure, would decrease the risk of t ype 1 diabetes in childhood. RESEARCH DESIGN AND METHODS - We conducted a systematic review of case-cont rol studies. Meta-analysis was performed to combine results, assess for het erogeneity, and explore variation in study design. RESULTS - Several generally well-designed case-control studies show a stati stically significant protective effect of day care on type 1 diabetes. Howe ver, meta-analysis revealed too much heterogeneity to accept the overall sy nthesis results and none of the studies used prerecorded data. Day care doe s seem to have a protective effect in the subgroup of children who will be diagnosed with type 1 diabetes before the age of 5 years (odds ratio = 0.6, 95% CI 0.5-0.8); however, this result is based on only two studies. CONCLUSIONS - Recall bias is one alternate explanation for these data confi rmation using prerecorded data is required. Such data could be prospectivel y measured in cohort studies of children at risk. We also suggest that info rmation about day care attendance be measured in randomized trials of agent s for the prevention of type 1 diabetes, as clay care exposure could potent ially modify the effect of the preventive agent.