Trends in blood folate and vitamin B-12 concentrations in the United States, 1988-2004

BACKGROUND:Monitoring the folate status of US population groups over time has been a public health priority for the past 2 decades, and the focus has been enhanced since the implementation of a folic acid fortification program in the mid-1990s. OBJECTIVE:We aimed to determine how population concentrations of serum and red blood cell (RBC) folate and serum vitamin B-12 have changed over the past 2 decades. DESIGN:Measurement of blood indicators of folate and vitamin B-12 status was conducted in [almost equal to]23 000 participants in the prefortification third National Health and Nutrition Examination Survey (NHANES III; 1988-1994) and in [almost equal to]8000 participants in 3 postfortification NHANES periods (together covering 1999-2004). RESULTS:Serum and RBC folate concentrations increased substantially (by 119-161% and 44-64%, respectively) in each age group in the first postfortification survey period and then declined slightly (by 5-13% and 6-9%, respectively) in most age groups between the first and third postfortification survey periods. Serum vitamin B-12 concentrations did not change appreciably. Prevalence estimates of low serum and RBC folate concentrations declined in women of childbearing age from before to after fortification (from 21% to