WEDNESDAY, June 28 (HealthDay News) -- Using B vitamins to lower levels of the blood protein homocysteine does not ward off Alzheimer's disease, at least not in older people with high homocysteine levels, according to new research.

The findings come as a disappointment after previous work had suggested a link between Alzheimer's and elevated concentrations of the amino acid.

"There is no short-term benefit of homocysteine lowering with B-vitamins on cognitive performance in healthy older people with high homocysteine," confirmed Murray Skeaff, co-author of the study published in the June 29 issue of the New England Journal of Medicine and associate professor of human nutrition at the University of Otago in Dunedin, New Zealand.

But the issue is not dead, yet.

"We would love to see something as simple and relatively non-toxic as a vitamin intervention that would prevent dementia and/or Alzheimer's," said William Thies, vice president of medical and scientific relations at the Alzheimer's Association in Chicago. "This trial probably has an inadequate number of people and too short a time period to show an effect. This particular trial will not end the discussion," he said.

Previous observational studies had shown higher homocysteine levels in Alzheimer's patients. Also, among older adults, higher homocysteine levels were correlated with poorer performance on cognitive tests.

About 4.5 million people in the United States suffer from dementia, the association said, and many more experience some form of cognitive impairment.

The authors of this study wanted to see if lowering homocysteine levels had any impact on cognitive function in older adults.

The two-year study involved 276 healthy participants, age 65 or older, who had blood homocysteine levels above a certain threshold.

Participants were given a daily supplement containing 1,000 micrograms of folate, 500 micrograms of vitamin B12 and 10 milligrams of B6. Cognitive testing was done at the beginning of the study as well as after one and two years of treatment.

Folates are B-vitamin nutrients found in foods such as bananas and oranges, leafy green vegetables, asparagus, broccoli, liver, and many types of beans and peas.

Although homocysteine levels did become lower in the vitamin group, the researchers detected no significant differences in scores of mental functioning.

"We used a range of tests to assess specific aspects of cognition and found no evidence of better cognition in those who took vitamins," Skeaff said. "If dementia is at the extreme of the continuum of cognitive decline, then, according to the 'homocysteine hypothesis,' we might have expected better cognitive performance in the vitamins group. This did not happen. If there was a hint of anything -- the emphasis is on hint -- it was lower cognitive scores in the vitamins group" he said.

"This study puts a chink in [the hypothesis'] armor, because we did not find even a hint of better cognition in those who took the vitamins," Skeaff said, concluding, "Population-based screening for high homocysteine concentrations or treatment with high-dose B-vitamins to improve cognitive performance cannot be advocated, based on current evidence."

But to truly understand the effect of lowering homocysteine on dementia, much larger and longer trials would be needed, Thies said. Such trials are invariably expensive.

One interesting aside to the current study is that it did manage to demonstrably lower homocysteine levels, even in the United States, where foods like bread are already folate-enriched.

"That's always been one of the questions about doing a trial like this: Is there enough folic acid supplementation around the world now that it makes homocysteine lowering difficult to achieve in a 'real' population?" Thies asked. "They've shown they can do that, but obviously, it has virtually no effect on any of the cognitive markers," he said.

The U.S. Department of Agriculture began requiring that all grain products be fortified with folic acid in 1998. The supplement is key in helping prevent neural tube defects such as spina bifida in newborns.

There has been concern, however, that such fortification may not be safe for older people with vitamin B12 deficiency.

More information

For much more on Alzheimer's, visit the Alzheimer's Association.