Review question

Does oral vitamin B 12 have similar effects as intramuscular injections of vitamin B 12 for people with vitamin B 12 deficiency?

Background

Vitamin B 12 (cobalamin) is necessary for basic body functions, such as the growth and development of red blood cells and the nervous system. Vitamin B 12 deficiency (a lack of vitamin B 12 ) is very common. Many factors contribute to vitamin B 12 deficiency, such as age, blood disease, vegetarian diet, indigestion, use of drugs, as well as poor nutrition. Doctors are more likely to give vitamin B 12 using injections into the muscle ( intramuscular injection) because they may be unaware of the option to use oral vitamin B 12 or uncertain about how well it works.

Study characteristics

We found three randomised controlled studies (clinical studies where people are randomly put into one of two or more treatment groups). The studies randomised 153 participants (74 participants to oral vitamin B 12 and 79 participants to intramuscular vitamin B 12 ). Treatment duration and follow-up ranged between three and four months. The mean age of participants ranged from 39 to 72 years.

Key results

Two studies used 1000 μg/day oral vitamin B 12 and showed no relevant difference to intramuscularly applied vitamin B 12 with regard to vitamin B 12 blood levels. One trial used 2000 μg/day vitamin B 12 and showed higher vitamin B 12 blood levels in favour of oral vitamin B 12 . Two studies reported side effects. One study stated that no treatment-related side effects were seen in both the oral and intramuscular vitamin B 12 groups. One study reported that 2 of 30 participants in the oral vitamin B 12 group left the trial early due to side effects. Orally taken vitamin B 12 showed lower treatment-associated costs than intramuscular vitamin B 12 in one trial . No study reported on clinical signs and symptoms of vitamin B 12 deficiency (e.g. fatigue, depression, neurological complications), health-related quality of life, or acceptability of the treatment scheme.

Quality of the evidence

The overall quality of the evidence was low or very low, mainly due to the small number of included studies and the low numbers of participants in these studies.