20 Nov 2002

People diagnosed with Alzheimer's disease at age 65 will likely live more than twice as long as those diagnosed at age 90, according to a study in the current issue of the Archives of Neurology.

Ron Brookmeyer and colleagues at the Johns Hopkins University in Baltimore, Maryland, used data from the ongoing Baltimore Longitudinal Study of Aging (in particular, on the 921 study participants who have been seen at age 55 or older since 1985). The authors noted that the median 8.3-year life expectancy for 65-year-olds with AD was a 67 percent reduction in survival expectancy relative to overall survival among all study participants (in absolute terms, men with AD had 15.7, while women with AD had 18.6 fewer years to live). By contrast, an AD diagnosis at age 90 translated to a median survival of 3.4 years, only a 39 percent reduction in survival relative to the entire study population (1.9 years for men, 2.7 for women).

The authors caution that the participants in this study have a considerably higher life expectancy than does the general U.S. population, due most likely to their higher average standard of living as indicated by a higher average education level. This means that the absolute survival values found in the study will be higher, though the proportionate reductions should still be applicable to the population at large.

The authors suggest that their study, like another recent one (Wolfson et al., 2001), is more accurate than retrospective studies that typically exclude people who die shortly after diagnosis, leading to a "length" or "survivor" bias. Wolfson and colleagues, however, found only an overall survival expectation of 3.3 years following AD diagnosis.—Hakon Heimer