Context: There are limited and controversial data concerning the relationships between retinol binding protein (RBP4), weight status, and insulin resistance in obese humans and especially in children.

Objective: To study the longitudinal relationships between RBP4, insulin resistance and weight status in obese children.

Design: One-year longitudinal follow-up study.

Setting: Primary care.

Patients: 43 obese children (median age 10.8y) and 19 lean children of same age and gender.

Intervention: Outpatient one-year intervention program based on exercise, behavior and nutrition therapy.

Main Outcomes Measures: Changes of weight status (SDS-BMI), RBP4, molar ratio RBP4/serum retinol (SR), insulin resistance index HOMA (homeostatis model assessment) and QUICKI (quantitative insulin sensitivity check index).

Results: Obese children had significantly (p<0.01) higher RBP4 concentrations and a higher RBP4/SR ratio as compared to lean children. In multiple linear regression analyses adjusted to age, gender and pubertal stage, RBP4 was significantly correlated to insulin and BMI. Pubertal children demonstrated significantly decreased QUICKI index and significantly increased HOMA index, insulin, and RBP4 concentrations compared to prepubertal children. Changes of RBP4 correlated significantly to changes of insulin (r=0.29), HOMA index (r=0.29), QUICKI (r=0.22), and weight status (r=0.31). Substantial weight loss in 25 children led to a significant (p<0.001) decrease of RBP4, RBP4/SR, blood pressure, triglycerides, insulin, and HOMA index and a increase in QUICKI in contrast to the 18 children without substantial weight loss.

Conclusion: RBP4 levels were related to weight status and insulin resistance in both cross-sectional and longitudinal analyses, suggesting a relationship between RBP4, obesity, and insulin resistance in children.