Serum retinol, the acute phase response, and the apparent misclassification of vitamin A status in the third National Health and Nutrition Examination Survey

Background: Serum retinol decreases transiently during the acute phase resp onse and can thus result in misclassification of vitamin A status. Objective: Our objective was to determine the prevalence of acute phase res ponse activation in a representative sample of the US population, identify the factors associated with this activation, and determine whether persons with an active acute phase response have lower serum retinol concentrations . Design: Data from the third National Health and Nutrition Examination Surve y (NHANES III) were analyzed. A serum C-reactive protein (CRP) concentratio n greater than or equal to 10 mg/L indicated an active acute phase response . Results: Mean serum retinol was lowest in subjects aged <10 y and increased with age. Concentrations were higher in males than in females aged 20-59 y . The prevalence of a CRP concentration <greater than or equal to>10 mg/L w as lowest in subjects aged <20 y (<less than or equal to>4%) and increased with age to a maximum of nearly 15%. An elevated CRP concentration was 2.4- fold greater in females than in males aged 20-59 y. Serum retinol was lower in subjects with elevated CRP concentrations. Conclusions: Serum retinol increases with age and males have higher mean va lues than do females aged 20-59 y. The prevalence of a CRP concentration gr eater than or equal to 10 mg/L also increases with age, is 2-fold greater i n females than in males aged 20-69 y, and is associated with common inflamm atory conditions. Thus, inflammation appeared to contribute to the misclass ification of vitamin A status in the NHANES III population, and serum CRP i s useful in identifying subjects who may be misclassified.