London , England ( CNN ) -- Daily doses of vitamin B can halve the rate of brain shrinkage in elderly people with mild cognitive impairment ( MCI ) , which can be a precursor to Alzheimer 's , researchers at Oxford University said Thursday . The two-year clinical trial is the largest to study the effect of vitamin B on MCI and one of the first disease-modifying trials in the Alzheimer 's field to show positive results , the researchers said . The study followed 168 volunteers with mild memory problems , half of whom took a high-dose vitamin B tablet for two years and the other half who took a placebo . Around one in six people age 70 and older has MCI and experiences problems with memory , language , or other mental functions , but not to a degree that interferes with daily life , the researchers said . Around half of those with MCI develop dementia , mainly Alzheimer 's , within five years of diagnosis . Certain B vitamins such as folic acid , vitamin B6 and vitamin B12 , are known to control levels of the amino acid homocysteine in the blood . High levels of homocysteine are associated with an increased risk of Alzheimers . Researchers used MRI scans to measure the rate of brain shrinkage over a two-year period . They found that on average , the brains of those taking a tablet that combined folic acid and vitamins B6 and B12 shrank at a rate of 0.76 percent a year , while those in the placebo group had a mean brain shrinkage rate of 1.08 percent . Those with the highest levels of homocysteine benefited most , with atrophy rates on treatment that were half of those taking the placebo , researchers said . Because the rate of brain shrinkage is known to be more rapid in those with MCI who go on to develop Alzheimer 's , it is possible that the vitamin treatment could slow down the development of the disease , they said . The researchers cautioned , however , that the relatively small number of participants and the short time span of the study meant more research is needed . `` These are immensely promising results , but we do need to do more trials to conclude whether these particular B vitamins can slow or prevent development of Alzheimer 's , '' said David Smith of the Department of Pharmacology at Oxford and a co-leader of the trial . `` So I would n't yet recommend that anyone getting a bit older and beginning to be worried about memory lapses should rush out and buy vitamin B supplements without seeing a doctor . '' The study was co-funded by the Alzheimer 's Research Trust , a British research charity . Chief Executive Rebecca Wood said the results are important but also said they require further study . `` The strong findings must inspire an expanded trial to follow people expected to develop Alzheimer 's , and we hope for further success , '' she said . The Alzheimer 's Association also raised concerns about the study noting the small size , the fact that it was conducted at a single research center and that one of the researchers involved has patents in this area and might , under certain circumstances , result in his financially benefit . `` I do n't think age was an issue in the effectiveness of the intervention , in this study . Homocysteine levels were . Only people with elevated homocysteine in the study showed benefit from the intervention . People with the lowest homocysteine levels in the study saw no benefit . So , B vitamins -- if it shown to be effective in further studies -- are unlikely to be beneficial for everyone , particularly if you already have healthy homocysteine levels , '' said William Thies , chief medical and scientific officer of the Alzeimer 's Association . `` Clearly , this is not enough data to go on . No conclusions can be drawn from this single study about use of B vitamins in MCI ( or Alzheimer 's disease or related dementias ) . No recommendations can or should be made to doctors or the public regarding use of B vitamins based on this study . No clinical or personal habits should be changed as a result of this article . '' The findings were published in the September issue of PLoS ONE , the journal of the non-profit Public Library of Science . The trial was supported by grants from Charles Wolfson Charitable Trust , Medical Research Council , Alzheimer 's Research Trust , Henry Smith Charity , Thames Valley Dementias and Neurodegenerative Diseases Research Network of the National Institute for Health Research , John Coates Charitable Trust , Sidney and Elizabeth Corob Charitable Trust , and Meda AB/Recip AB , which also donated the vitamin and placebo tablets .
Vitamin B could halve the rate of brain shrinkage in those with mild cognitive impairment . MCI can be a precursor to Alzheimer 's and other forms of dementia . The benefits of certain B vitamins are already known . Researchers caution that further and larger studies are needed to confirm the results .