Inflammation Does Not Mediate Relationships between BMI/BMI-for-Age Z-Score and Retinol or Retinol-Binding Protein in Adult Women or Young Children without Underweight, Wasting, or Malaria: An Analysis of 24 Surveys

Background: The extent to which inflammation from overweight or obesity influences interpretation of commonly used vitamin A status biomarkers is uncertain. Objectives: We examined relationships among weight status, inflammation, and retinol or retinol-binding protein (RBP) among women (15-49 y) and children (6-59 mo) with normal weight to overweight or obesity. Methods: -score (BAZ, children), inflammatory biomarkers C-reactive protein (CRP) and/or α1-acid glycoprotein (AGP), and retinol or RBP by linear regression. We also examined potential mediation by CRP and/or AGP in relationships between BMI/BAZ and retinol/RBP with structural equation modeling. Regression and mediation models accounted for complex survey designs and were adjusted for potential confounders. Results: Among women, BMI was positively associated with retinol/RBP in 5 of 13 surveys and positively associated with CRP and/or AGP in 10 of 13 surveys; associations between biomarkers of inflammation and retinol/RBP varied in direction and magnitude. Among children, BAZ was positively associated with retinol/RBP in 3 of 22 surveys and positively associated with CRP in 1 survey (none with AGP); inflammation biomarkers were consistently negatively associated with retinol/RBP. In 3 of 13 women's surveys and 1 of 22 children's surveys, inflammation partially mediated the relationship between BMI/BAZ and retinol/RBP; however, the direction of associations varied. Conclusions: In these surveys limited to individuals without undernutrition or malaria, inflammation associated with overweight or obesity does not appear to impact vitamin A assessment when measured with retinol/RBP. However, findings support measurement of biomarkers reflecting inflammation (of any source) to interpret vitamin A status, particularly among children.