Much of the research into the importance of folate and B12 levels has centered on seniors, and there is now quite a lot of research pointing to the need for adequate levels of these vitamins for maintaining cognitive functioning as you get older. In particular, high levels of homocysteine increase the risk of developing Alzheimer’s, and these go hand-in-hand with low levels of B12 and folate. Homocysteine is produced by the breakdown of a dietary protein called methionine, and B-vitamins are required to convert homocysteine back to methionine. Mouse research indicates that increased levels of homocysteine impair cognition through microvascular changes in the hippocampus. Greater brain atrophy is also found in those with high levels of homocysteine.
Elevated levels of homocysteine are not only associated with a significantly greater risk of developing Alzheimer's, they also dramatically increase the risk for stroke and vascular dementia.
Excitingly, though, a study found that vitamin B supplements markedly reduced brain atrophy in older adults with mild cognitive impairment, offering hope that they may be effective in delaying the development of Alzheimer’s. The benefits were greatest for those with the highest levels of homocysteine.
Higher levels of homocysteine are also linked with smoking.
Folic acid levels are of course also regarded as crucial when the brain is developing, which is why pregnant women are urged to take supplements, and why some countries fortify their bread with it.
There has been much less research on the effects of B-vitamins outside of the areas of prenatal development and age-related cognitive impairment and dementia. However, one study, carried out in a country which doesn't fortify its flour with folic acid, found significant academic achievement between those in the top third of folic acid intake and those in the bottom third.
Although the evidence for the age-related cognitive benefits of B12 and folate is greater than for any other supplement, not all studies have come out proclaiming their value. The inconsistencies may be explained by a finding that seniors with normal levels of vitamin B12 performed better if folate level was high, but when vitamin B12 was low, high levels of folate were associated with poor cognitive performance, as well as a greater probability of anemia.
Folate is a water-soluble B vitamin found particularly in citrus fruit, green leafy vegetables, whole-wheat bread, water-soluble dried beans and peas; however, they are often destroyed by cooking or processing. In the United States, Canada and Australia, flour is fortified with folic acid. Vitamin B12 is naturally found in animal foods including fish, milk and milk products, eggs, meat, and poultry. Vitamin B12 is often deficient in older people.