Study participants who took vitamin B and folate supplements fared no better on memory and thinking tests than participants who took a placebo.
The study - published in the journal Neurology and led by Rosalie Dhonukshe-Rutten, PhD, of Wageningen University in the Netherlands - is one of the largest so far to assess long-term supplement use and links to thinking and memory.
A 2010 study published in the same journal reported a link between vitamin B12 levels and memory loss, though the researchers concluded that more research was needed to confirm their findings "before vitamin B12 should be used solely as a supplement to help protect memory."
The team from this latest study notes that the prevalence of dementia is dramatically increasing. However, a potential modifiable dementia risk factor is an elevated plasma homocysteine (Hcy) level.
They explain that Hcy - an amino acid - may be toxic for neurons and vascular endothelial cells, and previous studies have shown links between higher Hcy levels and memory loss and Alzheimer's disease.
"Since homocysteine levels can be lowered with folic acid and vitamin B12 supplements, the hope has been that taking these vitamins could also reduce the risk of memory loss and Alzheimer's disease," explains Dhonukshe-Rutten.
'Supplementation yielded no difference in thinking and memory test scores'
To further analyze the link between memory and supplementation, the researchers followed 2,919 people with an average age of 74 who were part of the B-Vitamins for the Prevention of Osteoporotic Fractures (B-PROOF) study.
Each participant took either a tablet with 400 μg of folic acid and 500 μg of vitamin B12 or a placebo every day for 2 years. At the beginning and end of the study, the participants took part in tests of memory and thinking skills, and the researchers note that all participants had high Hcy blood levels.
Dhonukshe-Rutten says that although "the homocysteine levels decreased by more in the group taking the B vitamins than in the group taking the placebo, unfortunately there was no difference between the two groups in the scores on the thinking and memory tests."
There were several strengths to the study, including its large sample size and the use of validated neuropsychological tests, which made it possible for the team to study the effects of B vitamins on a wide range of cognitive functions that decline with age.
However, there were also some limitations. One limitation is that both groups of participants received vitamin D3, high concentrations of which have been linked with better cognitive performance and lower risk of dementia. As such, there is a possibility that vitamin D supplementation "diluted potential effects of vitamin B12 and folic acid on cognitive performance."
Another limitation of the study is that it lacks intermediate measurements, making follow-up measurements impossible.
Speaking with Medical News Today, Dhonukshe-Rutten said:
"To unravel the effects of B vitamins, a closer look into early brain pathologies would be useful to uncover subtle effects that are difficult to detect with paper and pencil tests.
We have anticipated on these innovative developments, and results from the B-PROOF study regarding MRI scans are awaited."
She added that "whole diet studies are needed, as synergy between nutrients seems to be important."
Concluding their research, the team writes that the "study provides Class 1 evidence that 2-year supplementation with folic acid and vitamin B12 in hyperhomocysteinemic elderly people does not affect cognitive performance."
Medical News Today recently reported on a study that suggested anxiety may speed up Alzheimer's in individuals with mild cognitive impairment.