Alzheimer’s disease and the related dementias are already a tremen¬dous burden to developed countries and an increasing burden to less developed regions. A summary of 46 studies done around the world (but mostly in Western countries) between 1945 and 1985 shows wide variation in prevalence of dementia for those > 65 yr of age, ranging from 1.3% (severe dementia only) in Sweden in 1969 to 20.3% in the USA (St. Louis) in 1984. On average, the prevalence of mild to severe dementia worldwide is about 10% for those ? 65 yr.
Until recently, few studies were done in any non-Western country other than Japan. Although studies done in China in the 1980s sug¬gested a surprisingly low prevalence of dementia (0.46% to 1.86%), a recent study in Shanghai reports rates of 12.3% for those > 75 and 24.3% for those > 85. In Japan, multi-infarct dementia appears to be more common than Alzheimer’s disease.
The prevalence of dementia increases logarithmically with age. For those aged 60 to 64 yr, the estimated prevalence is 0.7%, but for those aged 90 to 95 yr, it is 38.6%. Recent studies show prevalence rates of 28.8%inGothenberg, Sweden, for those > 85; 47.2% in East Boston for those > 80; and 25.3% in Rochester, Minn., for those > 80.
Biologic and ethnic differences may account for some of the differ¬ences in prevalence of dementia, as they do for heart disease and cancer prevalence. More likely, prevalence varies because of differences in di¬agnostic criteria and methods as well as difficulties in distinguishing true dementia from normal changes in cognition that occur with aging. Unless dementia can be cured or prevented, the number of elderly per¬sons with the disorder will continue to rise, placing an ever-increasing burden on caregivers, societies, and health care systems around the world.

Alzheimer’s disease and the related dementias are already a tremendous burden to developed countries and an increasing burden to less developed regions. A summary of 46 studies done around the world (but mostly in Western countries) between 1945 and 1985 shows wide variation in prevalence of dementia for those > 65 yr of age, ranging from 1.3% (severe dementia only) in Sweden in 1969 to 20.3% in the USA (St. Louis) in 1984. On average, the prevalence of mild to severe dementia worldwide is about 10% for those ? 65 yr.
Until recently, few studies were done in any non-Western country other than Japan. Although studies done in China in the 1980s suggested a surprisingly low prevalence of dementia (0.46% to 1.86%), a recent study in Shanghai reports rates of 12.3% for those > 75 and 24.3% for those > 85. In Japan, multi-infarct dementia appears to be more common than Alzheimer’s disease.
The prevalence of dementia increases logarithmically with age. For those aged 60 to 64 yr, the estimated prevalence is 0.7%, but for those aged 90 to 95 yr, it is 38.6%. Recent studies show prevalence rates of 28.8%inGothenberg, Sweden, for those > 85; 47.2% in East Boston for those > 80; and 25.3% in Rochester, Minn., for those > 80.
Biologic and ethnic differences may account for some of the differences in prevalence of dementia, as they do for heart disease and cancer prevalence. More likely, prevalence varies because of differences in diagnostic criteria and methods as well as difficulties in distinguishing true dementia from normal changes in cognition that occur with aging. Unless dementia can be cured or prevented, the number of elderly persons with the disorder will continue to rise, placing an ever-increasing burden on caregivers, societies, and health care systems around the world.