Proportion of individuals with low serum vitamin B-12 concentrations without macrocytosis is higher in the post folic acid fortification period than in the pre folic acid fortification period.

BACKGROUND

Large intakes of folic acid may delay the diagnosis of vitamin B-12 deficiency, which could lead to irreversible neuropathy.

OBJECTIVE

The objective of this study was to determine whether the proportion of individuals with low serum vitamin B-12 without macrocytosis (undiagnosed vitamin B-12 deficiency) has increased in the post-folic acid fortification period.

DESIGN

Individuals aged >or=19 y with low serum vitamin B-12 (<258 pmol/L) and mean corpuscular volume (MCV) measured between 1995 and 2004 were identified from medical records. The proportion and odds ratios of individuals with low serum vitamin B-12 without macrocytosis by sex, race, and age according to prefortification (n = 86), perifortification (n = 138), and postfortification (n = 409) periods were determined.

RESULTS

MCV was significantly lower in the postfortification period (88.6 fL) than in the prefortification (94.4 fL; P < 0.001) and perifortification (90.6 fL; P = 0.007) periods. The proportion of subjects with low serum vitamin B-12 without macrocytosis was significantly higher in the postfortification (approximately 87%) and perifortification (approximately 85%) periods than in the prefortification period (approximately 70%; P < 0.001). In a sex-, race-, and age-adjusted analysis, the odds ratio for having low serum vitamin B-12 without macrocytosis was 3.0 (95% CI: 1.7, 5.2) in the postfortification period relative to the prefortification period.

CONCLUSIONS

Subjects with low serum vitamin B-12 were likely to be without macrocytosis in the postfortification period. MCV should not be used as a marker for vitamin B-12 insufficiency. It is possible that folic acid fortification may have led to a correction of macrocytosis associated with vitamin B-12 insufficiency.