Influence of age, sex and vitamin status on fasting and post-methionine load plasma homocysteine levels.

BACKGROUND AND OBJECTIVES To investigate the effects of age, sex and vitamin status on total plasma homocysteine (tHCy), both after fasting (FtHCy) and two hours post-methionine load (PML-tHCy). The secondary aim was to determine the reference values for FtHCy and PML-tHCy. DESIGN AND METHODS A cohort of apparently healthy volunteers underwent blood sampling for FtHCy, PML-tHCy, creatinine, serum folate, vitamin B12 and vitamin B6 (pyridoxal-5-phosphate, PLP). RESULTS In 147 subjects (M/F= 82/65, age range: 14-94 years), FtHCy was significantly higher in men than in women. In men, age and folate levels explained 20.5% and 19.0% of FtHCy variance, respectively. In women, age and vitamin B12 accounted for 22.6% and 17.8% of FtHCy variance, respectively. PML-tHCy was similar in men and women. PML-tHCy was negatively correlated with folate in both sexes, and with vitamin B12 and age in women only. Folate accounted for 20% of the variance of PML-tHCy in men, while in women vitamin B12 and PLP explained 40% and 20% of variance of PML-tHCy, respectively. The reference values of FtHCy and PML-tHCy were: 19.63 and 40.18 mol/L, respectively, for men under 45 years, 14.26 and 28.31 mol/L, respectively, for women under 45 years, 28.38 and 36.48 mol/L for men above 45 years, and 22.49 and 44.06 mol/L for women above 45 years. INTERPRETATION AND CONCLUSIONS Age, gender and vitamin status influence both FtHCy and PML-tHCy in normal subjects. Reference values should be calculated according to age and sex.