Oral vitamin B12 supplementation in pernicious anemia: a prospective cohort study

The absorption of vitamin B12 (B12) is hindered in pernicious anemia (PA) due to intrinsic factor deficiency. Traditionally, intramuscular B12 injections were the standard treatment, bypassing the impaired absorption. Although there is potential for oral B12 supplementation through passive enteral absorption, it is not commonly prescribed in PA due to limited studies assessing its efficacy. We aimed to assess the efficacy of oral B12 supplementation in PA. We enrolled participants diagnosed with incident B12 deficiency related to PA. The diagnosis of PA was based on the presence of classical immune gastritis and of anti-intrinsic factor and/or anti-parietal cell antibodies. To evaluate the B12 status, we measured total plasma B12, plasma homocysteine, plasma methylmalonic acid (pMMA), and urinary methylmalonic acid/creatinine ratio. Participants were treated with oral cyanocobalamin at a dosage of 1000 μg/day throughout the study duration. Clinical and biological B12 deficiency-related features were prospectively and systematically assessed over the one-year study duration. We included 26 patients with B12 deficiency revealing PA. Following one month of oral B12 supplementation, 88.5% of patients were no longer deficient in B12, with significant improvement of plasma B12 (407 [297-485] vs 148 [116-213] pmol/L, p<0.0001), plasma homocysteine (13.5 [10.9-29.8] vs 18.6 [13.7-46.8] μmol/L, p<0.0001), and pMMA (0.24 [0.16-0.38] vs 0.56 [0.28-1.09] pmol/L, p<0.0001) levels compared to baseline. The enhancement of these biological parameters persisted throughout the 12-month follow-up, with no patients showing B12 deficiency by the end of the follow-up period. The median time to reverse initial B12 deficiency abnormalities ranged from 1 month for hemolysis to 4 months for mucosal symptoms. Oral supplementation with 1000 μg/day of cyanocobalamin improved B12 deficiency in PA.