No effect of vitamin B-12 treatment on cognitive function and depression: a randomized placebo controlled study

Background: Associations between vitamin B-12 deficiency and impaired cognitive function and depression have been reported. Methods: A randomized placebo controlled study including 140 individuals with an increased plasma methylmalonic acid (0.40–2.00 μmol/l) not previously treated with vitamin B-12. Cognitive function was assessed by the Cambridge Cognitive Examination (CAMCOG), Mini-Mental State Examination (MMSE), and a 12-words learning test. Symptoms of depression were evaluated by the Major Depression Inventory. The main outcome measure was change in cognitive function and depression score from baseline to follow-up 3 months later. Results: At baseline 78 (56%) individuals had cognitive impairment judged from the CAMCOG score and 40 (29%) according to the MMSE; 18 (13%) individuals had symptoms of depression. No improvement was found in cognitive function comparing the treatment and placebo group (total CAMCOG score: P=0.43), nor among individuals with only slightly impaired cognitive function (n=44, total CAMCOG score: P=0.42). The treatment group did not improve in depression score as compared to the placebo group (P=0.18). Limitations: The duration of impaired cognitive function was unknown. Conclusions: A high proportion of individuals with an increased plasma methylmalonic acid had impaired cognitive function, and a rather high prevalence of depression was observed. However, vitamin B-12 treatment did not improve cognitive function or symptoms of depression within the 3-months study period.