Vitamin B12 status and neurological function in older people

Ageing is associated with a decline in vitamin B12 status. Overt vitamin B12 deficiency can lead to neurologic disturbances but the public health impact for neurological disease of moderately low vitamin B12 status in older people is unclear. This study aimed to assess the relationship between vitamin B12 status and neurologic function in older people by systematically reviewing existing evidence and conducting secondary analyses on an existing high quality dataset. A systematic review of observational studies showed limited evidence of an association of vitamin B12 status with neurological function in older people. The possibility of an association between vitamin B12 status and neurologic function was further explored in cross-sectional analyses of baseline data from the Older People and Enhanced Neurological Function (OPEN) study, which investigated the effectiveness of vitamin B12 supplementation on electrophysiological indices of neurological function in asymptomatic older people with moderately low vitamin B12 status. This secondary analysis did not show any association between any measure of vitamin B12 status with electrophysiological indices or clinical markers of neurologic function. A systematic review of intervention studies suggested no benefits of vitamin B12 supplementation on neurologic function in asymptomatic older people; but it remained possible that improvement is only apparent in people with the lowest vitamin B12 status. This hypothesis was explored in further secondary analyses of OPEN data: there were no differences in the neurologic response to vitamin B12 supplementation according to baseline or change in vitamin B12 status. The available evidence indicates that concerns over the neurologic impact of moderately low vitamin B12 status in otherwise healthy older people may be unwarranted. Evidence is insufficient to support population screening for moderate vitamin B12 deficiency or population-wide recommendations for vitamin B12 supplementation in healthy asymptomatic older people, even among those with the lowest vitamin B12 status.