Effect of two different sublingual dosages of vitamin B12 on cobalamin nutritional status in vegans and vegetarians with a marginal deficiency : a randomized controlled trial

Background & Aims: Vegetarians and vegans are more vulnerable to vitamin B12 deficiency with severe risks of megaloblastic anemia, cognitive decline, neuropathy, and depression. An easy and simple method of supplementation consists of taking one weekly dosage of 2000 µg. However, single large oral doses of vitamin B12 are poorly absorbed. The present research evaluates the ability of two different sublingual dosages of vitamin B12 (350 µg/week vs. 2000 µg/week) in improving cyanocobalamin (vitamin B12) nutritional status in vegans and vegetarians with a marginal deficiency. Methods: A 12-week randomized, double-blind, controlled, parallel intervention trial was performed. Forty subjects with marginal vitamin B12 deficiency were enrolled and randomly divided into two groups: test group Ld (low dose, 350 µg/week) and control group Hd (high dose, 2000 µg/week) vitamin B12 supplementation. Blood samples were collected at baseline and after 15, 30, 60, and 90 days from the intervention for the determination of vitamin B12, related metabolic markers, and blood cell counts. Results: Two-way analysis of variance showed a significant effect of time (P < 0.0001) and of time x treatment interaction (P = 0.012) on serum concentration of vitamin B12. In particular, 90 days of supplementation increased the levels of cyanocobalamin (+81.8% in the Ld group and +144.0% in the Hd group) compared to baseline. A significant increase was observed for the levels of holotranscobalamin (+64.5% in the Ld group and +165.2% in the Hd group), while a decrease occurred for the levels of methylmalonic acid (-72.3% in the Ld group and -69.4% in the Hd group), homocysteine (-56.8% in the Ld group and -53.6% in the Hd group), and folate (-22.8% in the Ld group and -17.7% in the Hd group) compared to baseline (time effect, P < 0.0001). No difference was observed between groups (Ld vs. Hd). No effect was detected for the other variables under study. Conclusions: In our experimental conditions, both supplements were able to restore adequate serum concentrations of vitamin B12 and to improve the levels of related metabolic blood markers in subjects with a marginal deficiency. The results support the use of a sublingual dosage of 50 µg/day (350 µg/week) of cobalamin, instead of 2000 µg/week (provided as a single dose), to reach a state of nutritional adequacy of vitamin B12 in this target population.