Taking vitamin B12 and folic acid supplements may not reduce the risk of memory and thinking problems, a new study said Wednesday.

The study, published online in the U.S. journal Neurology, involved people with high blood levels of homocysteine, an amino acid that has been linked to 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," said study author Rosalie Dhonukshe-Rutten of Wageningen University in the Netherlands, in a statement.

In the study, 2,919 people with an average age of 74 took either a tablet with 400 micrograms of folic acid and 500 micrograms of vitamin B12 or a placebo every day for two years.

Tests of memory and thinking skills were performed at the beginning and end of the study.

All of the participants had high blood levels of homocysteine.

"While 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," said Dhonukshe- Rutten.

Early observational studies showed there may be some benefits to thinking and memory skills in taking folic acid and vitamin B12, but the results of later randomized, controlled trials were less convincing.