A review of published research has found no evidence that drugs, herbal products or vitamin supplements help prevent cognitive decline in healthy older adults.
The review, conducted at St. Michael's Hospital, found some evidence that mental exercises, such as computerized memory training programs, might help.
"This review provides some evidence to help clinicians and their patients address what strategies might prevent cognitive decline," said Dr. Raza Naqvi, a University of Toronto resident and lead author of the review.
The issue is of particular importance given that mild cognitive impairment affects 10 to 25 per cent of people over age 70. Mild cognitive impairment is characterized by reduced memory, judgment, and decision-making skills compared to someone of a similar age, but not enough to interfere with daily activities.
The annual rate of decline into dementia, such as Alzheimer's disease, is about 10 per cent. Given that rate and the aging population, it's estimated the number of Canadians with dementia will double to more than 1 million in the next 25 years.
Researchers including Dr. Sharon Straus, head of the Knowledge Translation Program at St. Michael's, reviewed 32 randomized clinical trials involving about 25,000 patients.
They found no strong evidence for pharmacologic treatments such as cholinesterase inhibitors that were developed to improve the effectiveness of acetylcholine, a chemical messenger that assists memory, thought and judgment.
Nor was there strong evidence that herbal supplements such as gingko improved cognitive functions or vitamins and fatty acids such as vitamin B6 or omega-3 fatty acids.
Some studies on estrogen actually indicated an increase in cognitive decline and dementia.
Evidence on the value of physical exercise, such as strength-training, was weak.
The strongest evidence was for the value of mental exercises such as computerized training programs or intensive one-on-one personal cognitive training in memory, reasoning, or speed of processing.
Dr. Naqvi said future studies should address the impact of cognitive training on the prevention of cognitive decline.
"We encourage researchers to consider easily accessible tools such as crossword puzzles and sudoko that have not been rigorously studied," he said. "The studies in this review that assessed cognitive exercises used exercises that were both labour- and resource-intensive, and thus may not be applicable to most of our patients."