Americans are living longer. That's the good news. The bad news is that the longer people live, the more likely they are to experience cognitive decline.
With the number of older Americans increasing, researchers around the country have thrown themselves into searching for ways to stave off mental decline, and the media stand ready to report every seeming breakthrough. Headlines have trumpeted such things as doing crossword puzzles, taking vitamin supplements, exercise and even drinking more red wine as possible ways of averting Alzheimer's disease and other kinds of dementia. But so far, there's no proof that any of them works.
Last month, the National Institutes of Health convened a State-of-the-Science Conference to evaluate and summarize current scientific evidence on preventing cognitive decline and Alzheimer's disease. The independent panel, which I chaired, concluded that rigorous studies have not yet conclusively demonstrated the value of any preventive measure for maintaining cognitive health, nor for delaying the onset or reducing the severity of Alzheimer's disease. The current state of knowledge about the natural history of Alzheimer's disease and about the aging process, together with inconsistent and varying definitions of Alzheimer's disease and cognitive decline, have hampered our understanding of what increases the risk of these conditions and how they may be prevented.
The fear that drives people to try to stave off Alzheimer's disease is understandable. This illness, which accounts for an estimated 60 percent to 80 percent of all dementia, robs people of their memories, their reasoning abilities and their personalities. Damage to the brain is progressive and leads ultimately to death. With an estimated 5.1 million Americans suffering from the disease, most of us have firsthand experience with its devastating effects. Alzheimer's disease is the fifth-leading cause of death in Americans age 65 and older, and the cost of this and other dementias in the U.S. is more than $148 billion annually. With the baby boomer generation nearing retirement age, those numbers are likely to increase.
But it's important to remember that for most people, cognitive performance remains relatively stable over their lifetime, with only a gradual decline in memory and processing speed. For others, this cognitive decline progresses to problems with memory, language or other essential cognitive functions that are severe enough to be noticed by others but not severe enough to interfere with daily life. In most people, this mild cognitive impairment does not progress to dementia. Dementia is the progressive deterioration of multiple aspects of cognitive ability including memory and at least one additional area — learning, orientation, language, comprehension or judgment — that is severe enough to interfere with daily life.
So what is our understanding of what causes dementia and how to prevent it? At present, age is the strongest known risk factor for Alzheimer's disease and cognitive decline. There is also evidence that diabetes mellitus, smoking, depression and a particular inherited variation of the ApoE gene are associated with higher risk of Alzheimer's disease and cognitive decline. Our panel reviewed many studies of lifestyle factors but concluded that so far, they show only weak or inconsistent associations. Studies examining the value of herbal and dietary supplements (including vitamins B, E and C, folate and beta-carotene), diet, physical activity and prescription and nonprescription drugs did not show any consistent benefit. There are other reasons, of course, to consume diets low in saturated fat and high in vegetable intake, and there is limited evidence that exercise may help preserve cognitive function. But although the panel believes that further study is warranted, these factors haven't yet been proved to prevent dementia.
The panel also identified gaps in scientific knowledge and made several recommendations for future research, such as the need for large, long-term, population-based studies using agreed-upon diagnostic criteria to characterize dementia and cognitive decline. It also called for the establishment of registries for Alzheimer's disease and cognitive decline, similar to those that exist for cancer. It will take considerable time and resources to conclusively identify factors that can modify risk and to recommend preventive measures based on firm scientific evidence.
With carefully designed future studies based on consistent definitions of diagnoses, we may one day have more answers. Until then, the best advice is to live a physically and mentally active healthy lifestyle, stay aware of well-known major risk factors for chronic diseases and avoid spending money on products with little or no proven benefit.
Martha L. Daviglus is a physician and professor of preventive medicine and gerontology at Northwestern University. She chaired the NIH State-of-the-Science Conference's Preventing Alzheimer's Disease and Cognitive Decline Panel.