Population studies of aging and cognition reveal that age appears to be associated with cognitive decline. In other words, as a population ages, the average cognitive ability of the population will decline. However, on an individual level, there is tremendous variation in cognitive change. An analysis of the large-scale Religious Orders Study supports the hypothesis that cognitive decline is not, in fact, a result of typical aging, but a result of specific causes affecting a subset of the population.
The Religious Orders Study is a longitudinal study of aging and Alzheimer’s among Catholic priests, nuns, and brothers living in different parts of the US, funded by the National Institute on Aging since 1993. Participants undergo a baseline evaluation that includes cognitive testing and assessment for dementia and other disorders. In addition to participating in cognitive and other testing at various intervals, participants agree to donate their brains for postmortem study.
For this analysis, the researchers analyzed a sample of more than 1,000 study participants who were age 75 or better at baseline. Based on recent findings within the field of cognitive aging, researchers hypothesized that, by examining individual changes in cognition over time, they would find subgroups that showed individuals with similar patterns of cognitive change. The researchers were also able to study the brains of some of the participants to look for signs of neuropathology that are associated with Alzheimer’s and other dementias.
Findings included three distinct subgroups among the population with different average rates of cognitive change. About two-thirds of the sample had very minimal cognitive decline; about a quarter showed moderate rates of decline; and less than 10 percent were part of a “fast decline” group. Individuals in the fast group were more likely to have signs of neuropathology than those in the minimal decline group, though 21 percent of studied brains in the minimal decline group showed these signs as well.
The population studied in this sample is not representative of the general population—these individuals were more educated than the general US population and had specific life course experiences in the Catholic Orders. Thus, it cannot be inferred from this study that, for example, two-thirds of all older adults will experience minimal cognitive changes at 75 years of age. However, this study adds further evidence that rapid cognitive decline should not be considered an expected consequence of aging.