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Around one sixth of people in the UK aged over 75 have vitamin B12 deficiency, which when severe can lead to significant problems in the nervous system including muscle weakness, problems with walking, tiredness, and pins and needles, as well as depression and problems with memory and other important everyday cognitive functions.  Vitamin B12 is found in everyday foods such as fish, meat, poultry, and dairy products.

There is clear evidence that individuals with severe vitamin B12 deficiency (with or without anaemia) benefit significantly from treatment.  However, there is uncertainty about the relevance of vitamin B12 treatment in non-anaemic individuals with moderate vitamin B12 levels.  Previous studies have suggested that people with moderate vitamin B12 deficiency have poorer nerve and memory functions.  The effects of daily supplementation with vitamin B12 to correct moderate deficiency on nervous system function were previously unknown.

Researchers from the London School of Hygiene and Tropical Medicine, King’s College London, UCL, and Oxford University conducted a double-blind randomised controlled trial of 201 people aged over 75 years.  Participants, who had moderate vitamin B12 deficiency and were not anaemic, received a tablet every day for one year containing either vitamin B12 or a placebo. At the end of the study after 12 months of supplementation, participants undertook clinical tests to assess their nervous system function including measures of muscle strength, coordination, mobility, tests of cognitive function including memory, and of psychological health. 

The researchers found no evidence of improved neurological or cognitive function among people who received vitamin B12 compared to those who received the placebo tablets.

Dr Alan Dangour, Reader in Food and Nutrition for Global Health at the London School of Hygiene & Tropical Medicine, said: 'This is the first trial of the effect of vitamin B12 supplementation on neurological and cognitive function in older people with moderate vitamin B12 deficiency.  Many people may be taking vitamin B12 supplements on a regular basis and it has been thought they would enhance function in older people.  Our study found no evidence of benefit for nervous system or cognitive function from 12 months of supplementation among older people with moderate vitamin B12 deficiency.'

Professor Robert Clarke, Professor of Epidemiology and Public Health at the University of Oxford, said 'The results are reassuring and demonstrate that older people with low blood levels of vitamin B12 in the absence of anaemia or definite vitamin B12 deficiency do not benefit from treatment with vitamin B12 supplements.'

Although the number of participants in the study was relatively small, the researchers report that it was sufficiently large to detect clinically relevant effects.  The supplements contained a safe recommended dose of vitamin B12, although it is possible that the dose may have been too low to affect neurological or cognitive function, or that the supplements might be needed for several years to have an impact.