Population reference values for plasma total homocysteine concentrations in US adults after the fortification of cereals with folic acid

BACKGROUND: Folic acid fortification has resulted in a dramatic increase in folate intake in the United States. Folate intake is inversely associated with circulating total homocysteine (tHcy). Elevated tHcy is directly associated with cardiovascular disease risk. OBJECTIVE: The aim of this study was to present the distribution of plasma concentrations of tHcy in US adults by using data from nationally representative sample surveys conducted since folic acid fortification was implemented. DESIGN: Data from the National Health and Nutrition Examination Surveys from 1999-2001 and 2001-2002 were used to study tHcy distribution by age, sex, and race-ethnicity in 9196 persons. RESULTS: Plasma concentrations of tHcy were higher in men than in women and in older persons than in younger persons. In those aged 19-30, 31-50, and 51-70 y but not in those aged >70 y, men had significantly (P < 0.0001) higher mean plasma concentrations of tHcy than did women. A race-ethnicity difference in plasma tHcy existed only in persons aged >70 y. Non-Hispanic blacks aged >70 y had significantly (P < 0.05) higher tHcy concentrations than did non-Hispanic white or Mexican American or Hispanic subjects in the same age group. Age-adjusted plasma tHcy concentrations did not differ significantly between non-Hispanic white (8.39 micromol/L), non-Hispanic black (8.92 micromol/L), and Mexican American or Hispanic (8.12 micromol/L) subjects. The rate of increase in plasma tHcy was greater in non-Hispanic blacks aged >/=50 y than in persons of similar age but of other races-ethnicities. CONCLUSIONS: These plasma tHcy data reflect the effects of folic acid fortification. Sex, age, and race-ethnicity differences persist in plasma tHcy concentrations.