Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency: a systematic review of randomized controlled trials

Background. Vitamin B12 deficiency is common, increasing with age. Most people are treated in primary care with intramuscular vitamin B12. Several studies have reported equal efficacy of oral administration of vitamin B12. Objectives. We set out to identify randomized controlled trial (RCT) evidence for the effectiveness of oral versus intramuscular vitamin B12 to treat vitamin B12 deficiency. Methods. We conducted a systematic review searching databases for relevant RCTs. Outcomes included levels of serum vitamin B12, total serum homocysteine and methylmalonic acid, haemoglobin and signs and symptoms of vitamin B12 deficiency. Results. Two RCTs comparing oral with intramuscular administration of vitamin B12 met our inclusion criteria. The trials recruited a total of 108 participants and followed up 93 of these from 90 days to 4 months. In one of the studies, mean serum vitamin B12 levels were significantly higher in the oral (643 ± 328 pg/ml; n = 18) compared with the intramuscular group (306 ± 118 pg/ml; n = 15) at 2 months (P < 0.001) and 4 months (1005 ± 595 versus 325 ± 165 pg/ml; P < 0.0005) and both groups had neurological responses. In the other study, serum vitamin B12 levels increased significantly in those receiving oral vitamin B12 and intramuscular vitamin B12 (P < 0.001). Conclusions. The evidence derived from these limited studies suggests that 2000 µg doses of oral vitamin B12 daily and 1000 µg doses initially daily and thereafter weekly and then monthly may be as effective as intramuscular administration in obtaining short-term haematological and neurological responses in vitamin B12-deficient patients