AGREEMENT AMONG INDICATORS OF VITAMIN-C STATUS

Agreement among three indicators of vitamin C status-serum ascorbate l evel, a 24-hour recall, and the frequency of fruit and vegetable consu mption-was examined using data from the Second National Health and Nut rition Examination Survey conducted between 1976 and 1980. Agreement b etween pairs of these indicators was good when assessed at the group l evel but inconsistent at the individual level, These indicators, when classified as continuous measures, had moderately good agreement (r = 0.45-0.54), whereas agreement was poor when classified as quartiles (k appa = 0.17-0.23), Agreement between clinically based categories of se rum ascorbate and total intake levels was poorer than expected (kappa = 0.25) as was agreement between low or deficient levels of both of th ese indicators (kappa = 0.3). Disagreement between low or deficient se rum and intake levels was greater in participants who were younger, Af rican American compared with white and other races, less educated, cur rent smokers, nonsupplement users, and examined in the winter compared with in the summer or fall. These findings suggest that the indicator s cannot be used interchangeably to assess vitamin C status because th ey distinguish between different aspects of status, intake level versu s serum level, an indicator of available pool. Moreover, depending upo n how these indicators are used in statistical analyses, they may clas sify individuals differently.