Mandatory folic acid fortification has been advocated as the most effective method of protecting against neural tube defect pregnancies on a population basis(Reference Oakley1). Most European countries have not proceeded due to concerns of putative masking of vitamin B12 deficiency. However, it is currently unknown what dose of folic acid masks vitamin B12 deficiency.
The aim of this study was to assess the effect of a physiological dose of folic acid (400 μg/d) on the haematological profile of those with suboptimal vitamin B12 status. Participants with serum vitamin B12 levels between 130 and 200 ng/l were given either folic acid or placebo daily for 6 months in a randomized, double-blind, placebo-controlled study. Fasting blood samples were collected pre-intervention and at monthly intervals until completion to determine vitamin B12, folate and haematological status (mean cell volume, Hb and haematocrit).
Fourteen volunteers in the placebo group and 15 volunteers in the folic acid group completed the 6-month intervention. Volunteers who were Fe-deficient were excluded from analysis. There were no significant differences in vitamin B status and haematological markers between groups pre-intervention. Significant responses to intervention occurred in serum folate (increased; P<0.001), red blood cell folate (increased; P=0.001) and plasma homocysteine (decreased; P=0.011) in the folic acid group. Consumption of 400 μg of folic acid per d had no significant effect on haematological profile. The table shows the numbers of volunteers who were defined as having a normal haematological status at each stage of intervention in each group.
NS: non-significant. McNemar's test was used to determine differences in haematological status pre- and post-intervention within groups (P<0.05).
This is the first folic acid supplementation trial in persons with apparent suboptimal vitamin B12 status. Both groups had a normal haematological profile pre-intervention suggesting that mean cell volume should not be the sole diagnostic marker used to identify possible vitamin B12 deficiency.