A cheap regimen of vitamins in use for decades is seen by scientists as a way to delay the start of Alzheimer's disease and dementia, a goal that prescription drugs have failed to achieve.

Drugmakers including Pfizer Inc. have spent billions on failed efforts to develop an effective treatment for dementia and Alzheimer's.

Now, in the latest of a steady drumbeat of research suggesting that diet, exercise, and socializing remain patients' best hope, a study published last week in the Proceedings of the National Academy of Sciences (PNAS) shows that Vitamins B6 and B12 combined with folic acid slowed atrophy of gray matter in brain areas affected by Alzheimer's.

"You don't have any other options for these patients, so why not try giving them this cocktail of B vitamins?" says Johan Lokk, head physician in the geriatric department at Karolinska University Hospital Huddinge in Sweden, who wasn't involved in the study.

Alzheimer's disease and dementia mostly affect older people. As people live longer, the number afflicted by the conditions is growing. Delaying dementia with a vitamin regimen may help slow the surge in cases, which the World Health Organization has predicted will more than triple from 36 million worldwide in 2010 to 115 million in 2050.

In the PNAS study, researchers tracked 156 people age 70 and older who had mild memory loss and high levels of homocysteine, a protein previously linked to dementia. The study found that the amount of gray matter declined 5.2 percent in those taking a placebo, compared with 0.6 percent in those who took the vitamin cocktail. The supplements cost about 30 cents a day in pharmacies.

"It's the first and only disease-modifying treatment that's worked," said A. David Smith, professor emeritus of pharmacology at Oxford University in England and the study's senior author. "We have proved the concept that you can modify the disease."

Older people's brains shrink about 0.5 percent a year from the age of 60, and faster in people with Vitamin B12 deficiency, mild cognitive impairment, or Alzheimer's disease, Smith said. If that pace can be slowed before full-blown Alzheimer's develops, it may delay the disease's progression so older people can enjoy better lives until they die from another cause.

The Oxford group studied people in the Oxford, England, area with mild cognitive impairment (MCI), or some memory loss. One in six people over 70 have MCI and about half of those develop dementia within five years, Smith said.

Study volunteers were given either a placebo or 0.5 milligram of Vitamin B12, 20 milligrams of Vitamin B6, and 0.8 milligram of folic acid. Their brains were scanned using magnetic-resonance imaging, and blood levels of the protein homocysteine were measured at the start of the trial and two years later. The MRI scans compared how much gray matter was lost in brain regions most affected by Alzheimer's disease.

"It's a big effect, much bigger than we would have dreamt of," Smith said. "I find the specificity of this staggering. We never dreamt it would be so specific."

The research reinforces past findings that supplements slowed brain atrophy and cognitive decline in the group. Smith and his Oxford colleagues reported in 2010 that the atrophy rate in patients' whole brains was reduced about 30 percent in those taking the vitamins and 53 percent in those on the vitamins who also had elevated homocysteine.

Vitamin B12 is found in liver, fish, and milk; folic acid, in fruit and vegetables. Deficiency of folate and B vitamins is already linked to dementia. Smith is studying whether less-than-optimal levels of B vitamins and folic acid contribute to its development.

"If you have somebody who has outright Alzheimer's disease, this isn't really going to help them much," said Joshua Miller, a nutrition professor at Rutgers University. "If you can catch them at an earlier level, they may be able to benefit from it, but only if you have elevated homocysteine."

Smith agreed. "We're not suggesting everyone over 60 take this; we're suggesting it should be targeted to people over 70 with high homocysteine and memory problems."