vitamin b12

Here, Professor Timothy Kwok discusses the impact of vitamin B12 on the brain health of older people

Vitamin B12 is a micronutrient which is essential to brain health. It is only present in meat or animal related foods e.g. egg and milk, and its digestion and absorption processes are elaborate and complicated. Older people and vegetarians especially vegans are therefore at risk of vitamin B12 deficiency. Some drugs also increase the risk of vitamin B12 deficiency by impairing its absorption e.g. peptic acid suppressing drugs, metformin for diabetes mellitus.

Vitamin B12 deficiency is a recognised cause of acute confusion and dementia in older people. Yet the clinical response of vitamin B12 replacement in older people with dementia is variable and most often unsatisfactory. We have observed the clinical response of vitamin B12 replacement in thirty older people with early dementia and vitamin B12 deficiency and found that they had significant improvement in confusion over nine months, but overall cognitive function did not improve significantly.(1)

A potential explanation why correction of vitamin B12 deficiency does not improve cognitive function in older people with dementia is that the brain damage from vitamin B12 deficiency is not completely reversible. It may, therefore, be important to detect vitamin B12 deficiency as early as possible. Unfortunately, vitamin B12 deficiency develops insidiously over a number of years and more often than not does not cause any apparent discomfort unless it is severe enough to cause anaemia and numbness of feet (when it affects the nerves).

vitamin b12

Our research group has been investigating the role of vitamin B12 deficiency in brain degeneration in older people before they develop dementia. Some time ago, we performed a trial of vitamin B12 replacement by intramuscular injections for three months in a group of older vegetarians with moderately severe vitamin B12 deficiency. We found that vitamin B12 supplementation led to improvement in visuospatial function.(2) Moreover, we also found in another trial of fifty vegetarians with significant vitamin B12 deficiency that vitamin B12 replacement could reverse the narrowing the blood vessels which is an important cause of brain degeneration with ageing.(3)

The next question which we tried to address is whether borderline low vitamin B12 status which is often the case in older people can also cause cognitive decline. We, therefore, performed a trial of oral vitamin B12 in 280 older people with diabetes mellitus and borderline low blood vitamin B12 concentrations. Half of them received the supplement while the rest took placebo tablets (which did not contain vitamin B12) for two years.

We found that the extent of cognitive decline was similar between the two trial groups, implying that vitamin B12 does not prevent cognitive decline in older people when vitamin B12 status is not in the deficiency range. However, the trial was not big enough to exclude the possibility that vitamin B12 supplement may benefit brain health in older people with borderline low vitamin B12 status over the longer term.

Overall, our research work over the years demonstrated that vitamin B12 can improve brain function in older people with vitamin B12 deficiency whether they have dementia or not. But there is no evidence that vitamin B12 supplement can improve cognitive function in those who are not deficient. Nevertheless, vitamin B12 deficiency can be detected easily by a simple blood test.

There is, therefore, a strong case for older people to have a screening blood test for vitamin B12 deficiency, even though they do not have any dementia symptom. Long term vitamin B12 supplement taken either orally or by intramuscular injections one to three monthly can be expected to preserve brain as well as vascular health in these people.


1 Kwok T; Lee J; Lam L; Woo J (2008) Vitamin B(12) supplementation did not improve cognition but reduced delirium in demented patients with vitamin B(12) deficiency. Archives of Gerontology & Geriatrics. 46(3):273-82

2 Kwok T; Tang C; Woo J; Lai WK; Law LK; Pang CP (1998) Randomized trial of the effect of supplementation on the cognitive function of older people with subnormal cobalamin levels. International Journal of Geriatric Psychiatry 13(9):611-6

3 Kwok T; Chook P; Qiao M; Tam L; Poon YK; Ahuja AT; Woo J; Celermajer DS; Woo KS (2012) Vitamin B-12 supplementation improves arterial function in vegetarians with subnormal vitamin B-12 status. Journal of Nutrition, Health & Aging. 16(6):569-73

4 Kwok T; Lee J; Ma RC; Wong SY; Kung K; Lam A; Ho CS; Lee V; Harrison J; Lam L (2017) A randomized placebo controlled trial of vitamin B12 supplementation to prevent cognitive decline in older diabetic people with borderline low serum vitamin B12. Clinical Nutrition. 36(6):1509-1515


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