VARIABILITY AND DETERMINANTS OF TOTAL HOMOCYSTEINE CONCENTRATIONS IN PLASMA IN AN ELDERLY POPULATION

The variability of plasma total homocysteine (tHcy) was examined in 96 individuals over a 1-yr period. Blood tHcy concentrations varied from 7.1 mu mol/L in the bottom quintile to 14.5 mu mol/L in the top quint ile. The mean tHcy was 10.4 mu mol/L, the between-person SD was 2.5 mu mol/L, and the within-person SD was 0.93 mu mol/L. There was little s easonal variation, and the reliability coefficient was 0.88. Mean tHcy concentrations were inversely related to mean plasma folate (r = -0.3 6) and vitamin B-12 (r = -0.35) concentrations. Median tHcy concentrat ions were similar to 1 mu mol/L higher in men than in women and in old er (70 to 74 years) than in younger (65 to 69 years) individuals and h igher in those with the TT and CT genotypes for the methylenetetrahydr ofolate reductase polymorphism than in those with the CC genotype (10. 7 and 10.6 vs 9.6 mu mol/L). Epidemiological studies based on single t Hcy measurements may underestimate the magnitude of any risk associati ons with disease by 10-15%.