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"The duration of survival following a diagnosis of Alzheimer's disease depends critically on the subject's age at diagnosis. The results of this study indicate that the median survival of patients with Alzheimer's disease could range from nearly 9 years for persons diagnosed at age 65 to approximately 3 years for persons diagnosed at age 90 years," said Ronald Brookmeyer, PhD, professor of biostatistics at the Johns Hopkins Bloomberg School of Public Health.

Data for the study was collected from the Baltimore Longitudinal Study of Aging, which began in 1958 to monitor the effects of aging. The participants were asked to return for follow-up visits every two years to be examined and to answer questionnaires. From this study, Dr. Brookmeyer and his colleagues selected 921 participants who were age 55 or older in 1985 and had received some follow-up visits. Alzheimer's disease was diagnosed using several neuropsychological tests and deaths were recorded through September 1999.

The statistical analysis found that the median survival times ranged from 8.3 years for people diagnosed at age 65 to 3.4 years for people diagnosed at age 90. Persons diagnosed with Alzheimer's disease at age 65 could anticipate a 67 percent reduction in life span compared to those without Alzheimer's disease, while persons diagnosed at age 90 could anticipate a 39 percent reduction in life span. The researchers say Alzheimer's disease is associated with a greater proportionate reduction of life span among patients affected at younger ages compared with older ages, presumably because patients at older ages are at higher risk of dying from other causes.

The researchers also reported that the average length of time between the onset of symptoms and the diagnosis of Alzheimer's disease was 2.8 years. However, they did not find any significant differences between men and women in survival after diagnosis of the disease.

"It is projected that in the next 50 years, the prevalence of Alzheimer's disease will quadruple with approximately 1 in 45 Americans living with the disease. Information on survival following diagnosis is important not only for predicting future prevalence of the disease, but also for planning the resources necessary to care for patients during a life span of increasing difficulty," said Dr. Brookmeyer.