Recruitment and retention of urban schoolchildren into a randomized double-blind vitamin D supplementation trial

Background: While rarely used for supplementation trials in the United States, schools present a practical alternative to a clinical setting. Purpose: We describe the successful recruitment and retention of urban schoolchildren into a 6-month randomized, double-blind vitamin D-3 supplementation trial. Methods: Boston-area urban schoolchildren, aged 8-15 years, were recruited in 2011-2012 through classroom and auditorium presentations. Informed consent forms in five languages were sent home to parents. Retention methods included regular telephone calls and gift cards for completed study visits. Results: In total, 691 schoolchildren enrolled. Their mean (standard deviation) age was 11.7 (1.4) years; 59% were racial/ethnic minorities and 68% qualified for free or reduced-price school meals. Multi-level, culturally sensitive, creative approaches contributed to success in recruitment and retention. Of 691 participants, 81% completed the 6-month intervention period. Reasons for attrition included missed appointments and fear of a blood draw. More children from households with higher incomes were retained than those from households with lower incomes (85% vs 79%, respectively, P=0.04). Limitations: The need for three fasting blood draws over the 6-month supplementation period was a limiting factor in the recruitment and retention of children in this study. Conclusion: Recruitment of urban children into a school-based randomized controlled trial represents a feasible approach for a supplementation study. Particular attention to children of lower socioeconomic status may enhance participation and retention when conducting intervention studies among diverse populations.