It is a truism that aging of populations will result in large and potentially unmanageable increases in the number of older adults with dementia.

Michael D. Hurd, a senior researcher with RAND, and colleagues estimated the present annual financial burden of dementia care in the United States is about $200 billion. Extrapolation of historic dementia rates among older adults project intimidating rises in dementia cases and costs.

Recent epidemiological data, however, indicate a more encouraging picture.

Results from the United Kingdom Cognitive Function and Aging Studies (CFAS) indicate an approximate 20-25 percent decline in age-specific prevalence and incidence of dementia over the past generation. Data from the U.S. Framingham Heart Study indicate a remarkable 40 percent decline in age-specific incidence of dementia over the past few decades.

These results are consistent with data from other population-based studies. CFAS investigators estimate that declining dementia incidence may lead to a plateau in the annual number of new cases of people with dementia.

Why the improvements? As a neurologist and a health policy expert who have studied the disease and the implications on our health care system, we have found two major factors in the declining dementia rates. If the factors continue, the burden of dementia in the future may be less than previously thought.