Interpretation of vitamin A status in apparently healthy Pakistani children by using markers of subclinical infection

Abstract

Background: Plasma retinol concentrations are depressed by infection but are commonly used to assess vitamin A status. Objective: We measured 2 acute phase proteins, α1-antichymotrypsin (ACT) and α1-acid glycoprotein (AGP), to determine whether they could be used to assist in interpreting vitamin A status. Design: In 1997, a 2-stage cluster-sampling procedure was used to select 3074 apparently healthy, 6-60-mo-old children from rural and urban areas of North West Frontier Province, Pakistan. Plasma retinol, ACT, AGP, and ferritin measurements and anthropometric measurements were obtained for 2519 children. Results: Median plasma retinol, ACT, AGP, and ferritin concentrations were 0.86 μmol/L, 0.39 g/L, 1.14 g/L, and 5.5 μg/L, respectively. There were no significant (P > 0.05) differences in retinol, ACT, or AGP by sex or age. Some 797 children (32%) had retinol concentrations < 0.7 μmol/L and 87 (4%) had retinol concentrations < 0.35 μmol/L; 274 children (11%) had elevated ACT (> 0.6 g/L) and 1141 (45%) had elevated AGP (> 1.2 g/L). Retinol concentration correlated with ACT (r = -0.141), AGP (r = -0.138), and ferritin (r = -0.09) (all P < 0.001), but stepwise multiple regression indicated that these 3 variables made a minimal although quantifiable contribution to the variance of retinol (ACT, r2 = 0.02; all 3 variables, r2 = 0.03). Conclusions: The transient depression in plasma retinol produced by subclinical infection increased the number of atrisk children by 10% (76 of 797) and 56% (49 of 87) for plasma retinol concentrations < 0.7 and < 0.35 μmol/L, respectively. In addition, dietary inadequacy may be responsible for retinol concentrations being ≃16% lower in Pakistani children than in children in the United Kingdom, where dietary vitamin A is adequate.