Rader and Yetley, in their recent letter,1 conclude that there is an inconsistency between the effect of increasing folic acid intake on serum folate levels based on the results of our randomized trial,2 and the effect based on the results of Lawrence and her colleagues,3,4 which compares serum folate levels before and after mandatory grain fortification with folic acid in the United States. Radar and Yetley take the view that the increase in serum folate from 1994 to 1999 (an increase of more than 7.4 ng/mL, from 12.6 ng/mL in 1994 and >20.0 ng/mL in 1999) reported by Lawrence and her colleagues is attributable to US grain fortification of flour that was introduced over 1996 and 1997 and was designed to increase the daily intake of folic acid by 0.1 mg/d. From our trial, an increased serum folate level of about 2.4 ng/mL would be expected for a 0.1-mg/d increase in folic acid intake.
Wald D, Law M, Wald N. The Serum Folate Response to the US Mandatory Fortification of Grain Products With Folic Acid. Arch Intern Med. 2002;162(19):2254. doi: