The new study, published in the journal Neurology, found that B vitamin induced reductions in homocysteine plasma levels are not associated with long term improvements in cognitive function, suggesting that daily supplementation may have no effects on long term mental functioning.
The research casts doubt on findings reported only last week, suggesting that B vitamins could help to prevent brain wastage and cognitive impairment.
“The most economical explanation for our findings… is that elevated plasma homocysteine is not a risk factor but merely a marker that reflects underlying common processes responsible for both dementia and high tHcy, and that homocysteine-lowering treatment with B-vitamins does not affect the long term cognitive function of people at risk,” wrote the researchers, led by Dr Andrew Ford, from the University of Western Australia.
Dietary supplementation has been seen as a potentially cheap and effective way of reducing the effects of health conditions that typically affect the elderly, such as cognitive decline and Alzheimer's.
Homocysteine is an amino acid, that is known to be a marker of cardiovascular disease risk. A high total plasma homocysteine (tHcy) has been associated with cognitive impairment and dementia – although the authors noted that it is unclear whether this link is causal.
Previous research has suggested that tHcy can be lowered by between 20 and 30 percent through oral supplementation of B vitamins, making tHcy a potential modifiable risk factor for cognitive function.
Earlier this month a study led by Prof David Smith from the University of Oxford observed that supplementation with B vitamins could lower plasma homocysteine levels by over 30 percent, and reduce brain shrinkage by almost 30 percent. The study suggested that B vitamins could act to reduce cognitive decline and mild cognitive impairment (MCI).
The new study, investigated the long term effects of vitamin B supplementation on cognitive function and MCI in a group of “at risk” older men.
Supplementation with B vitamins was reported decrease total plasma homocysteine by 22.5 percent – compared to a 10.7 percent increase in tHcy found in the placebo group.
The researchers reported that the vitamins were associated with “fleeting gains on measures of immediate recall and attention”, however such changes were not sustained in the long term.
Long term, B-vitamin supplementation was seen to have no benefit in terms of mortality or a later diagnosis of dementia.
Men receiving supplements were found to be 28 percent less likely to develop significant cognitive impairment than men in the placebo group – however, this finding was not statistically significant.
“The results of this trial indicate that the use of vitamins B6, B12 and folate for two years does not change the rate of cognitive decline amongst men with hypertension aged 75 years or older,” concluded the researchers.
The authors added that it could be possible that vitamin supplementation is more effective in people with pre-existing cognitive dysfunctions, “although our findings and those of others have not supported this view,” they added.
Published online ahead of print, doi:10.1212/WNL.0b013e3181f962c4
“Vitamins B12, B6, and folic acid for cognition in older men”
Authors: A. H. Ford, L. Flicker, H. Alfonso, J. Thomas, R. Clarnette, R. Martins, O. P. Almeida