Vitamin B supplements have no effect in slowing or preventing mental decline due to age, a new research shows.

The study shows that vitamin B also does not avoid the risk of Alzheimer's disease. For the study, researchers at the Oxford University analyzed clinical trial data of 22,000 people. They followed people taking vitamin B. This data was then compared to those on placebo.

The research analysis showed that people taking vitamin B had reduced levels of homocysteine in their blood by a quarter. High levels of homocysteine are seen in people with Alzheimer's.

However, no effect at all was seen on their mental abilities. Their global cognitive function and scores for specific mental processes such as memory, speed  and executive function were measured. No difference in scores of people on placebos and vitamin B was noticed

"It would have been very nice to have found something different," Robert Clarke of Oxford University who led the work, said in press release. "Our study draws a line under the debate: B vitamins don't reduce cognitive decline as we age. Taking folic acid and vitamin B-12 is sadly not going to prevent Alzheimer's disease."

The team said that folic acid taken before and during early pregnancy reduces a woman's risk of having a neural tube defect birth problem. But, they doubt it has any benefit against cognitive decline.

"One in three people over the age of 65 will develop dementia and yet research funding lags behind other conditions and we haven't seen a new treatment made available in a decade," said James Pickett, Head of Research at Alzheimer's Society. "We need to see significantly more investment and recruit the next generation of leaders in research in order to deliver breakthroughs that could prove so vital to those affected by the condition."

The findings are published in the American Journal of Clinical Nutrition.