"Forgot where you left your keys The name of your neighbors kid Whether you locked the car Anyone looking for an easy way to boost brain power is likely to come across an increasingly common piece of advice Up your intake of B vitamins. The vitamins  including folic acid and vitamins B and B  are often touted as a way to improve memory and stave off cognitive decline. The claims are based on the finding that levels of the vitamin are low in people with various forms of cognitive impairment including dementia and Alzheimers disease. But experts say its still unclear whether taking high doses of the vitamins will keep such conditions at bay. I dont know that people need to rush out and buy B vitamins  I dont think were ready for that yet says Mary Haan an epidemiology professor at UC San Francisco who has studied the relationship between B vitamin intake and cognitive function in elderly adults.   Researchers believe B vitamins may affect brain health because of their ability to lower blood levels of an amino acid called homocysteine. In the s several studies documented high levels of homocysteine in people with cognitive impairment and dementia. But at the time scientists didnt know whether high levels of the amino acid caused cognitive decline or whether cognitive decline caused people to accumulate high levels of the amino acid. To determine which came first researchers at Boston University followed approximately  healthy adults who were enrolled in the ongoing Framingham Heart Study which began in  to identify risk factors for heart disease. At the end of eight years the researchers found that the rates of dementia and Alzheimers disease were higher in people who had had high homocysteine levels compared with those who had low levels. Their conclusions  that high homocysteine levels increase a persons risk of dementia and Alzheimers disease  were published in the New England Journal of Medicine in . Since then a handful of studies have administered high doses of homocysteinelowering B vitamins to subjects in order to determine the vitamins effects on brain function. The results have so far been mixed with only a minority of studies showing a benefit says Joshua Miller a professor of pathology and laboratory medicine at UC Davis who studies the vitamins. In one such study researchers in New Zealand administered either high doses of vitamins B B and folic acid or a placebo to  older adults with at least  micromoles of homocysteine per liter of blood. Normal levels of the amino acid range from  to  micromoles per liter. The group that took the vitamins did see its homocysteine levels drop to normal but its members performed no better on cognitive tests than those in the group that took the placebo. The twoyear study was published in the New England Journal of Medicine in . In another study published in the Lancet in  Dutch researchers randomly assigned more than  older adults to take either high doses of those same B vitamins or a placebo every day for three years. In this case the group that took the B vitamins not only experienced a drop in homocysteine levels but also performed better on tests of memory and information processing. But a third study published in the Journal of the American Medical Assn. in  assigned a group of  Alzheimers patients to take either high doses of B vitamins or a placebo every day for a year  and found no improvement in cognitive ability. A comprehensive review of the most rigorous studies of the B vitamins and brain function published by the nonprofit Cochrane Collaboration in  determined that there was no consistent evidence that folic acid or vitamin B improved cognitive function. The review excluded vitamin B.   Haan says the existing body of studies may be inconclusive because the causes of cognitive decline  which are incompletely understood  are probably too complex to be halted with a single vitamin supplement. And adds Miller its possible that future studies will show that the vitamins are helpful to only a subset of adults such as those with very high homocysteine levels or early signs of cognitive impairment. He points to a recent study in which brain atrophy or shrinkage which occurs in older people who are losing brain function slowed by  in elderly patients with both high homocysteine levels and mild cognitive impairment who took a B vitamin pill daily for two years. Brain shrinkage occurred at a rate of about . in the people taking B vitamins in the study compared with a rate of . per year in a group that took a placebo. This doesnt mean that these people wont get worse over the long term says Miller who was not involved in the study. It means that the vitamins slowed the process down. Adults need at least  to  micrograms of folic acid . micrograms of vitamin B and between . and . micrograms of vitamin B daily. Amounts in these brain studies were greater than that  as much as  micrograms of folic acid  micrograms of vitamin B and up to  milligrams of vitamin B. Such high doses can have negative side effects Too much B can cause numbness and insensitivity in the hands and feet and too much folic acid may confusingly either mask or exacerbate symptoms of vitamin B deficiency. To some tingling in the extremities may seem a fair price to pay for the possibility of delaying cognitive decline. But Haan stresses that the evidence in favor of taking B vitamins is still far too preliminary to act upon because there havent been enough well designed randomized trials on the subject. What we believe now could be disproven in a heartbeat she says."