Cognitive impairment and survival at older ages
In: Finch, C. E., Christen, Y., Robine, J.-M. (Eds.): Brain and longevity, 131–144
Research and perspectives in longevity -
Berlin [et al.], Springer (2003)
Several studies suggest that cognitive impairment is a risk factor for mortality among older adults. However, the mechanisms that generate the association between cognitive function and survival are not well understood. Proposals attempting to explain why the association is observed focus on the role of health and diseases and on terminal decline. Poor health may affect both cognitive function and survival, and the association between cognitive impairment and mortality could be spurious. The terminal decline hypothesis suggests that factors related to the death of the individual cause a decline in intellectual performance, and that the onset of this decline may be detected in some instances several years prior to the death of the persons.
We investigated these issues in a sample of 2,401 Danish twins aged 75 years and older. At baseline in 1995 the Mini-Mental State Exam was administered to assess participants’ cognitive functioning, and subjective and objective health measures were also collected. We related cognitive function to 6-year survival. As expected, cognitive impairment was associated with an increased risk of death. Interestingly, this effect was attenuated but not eliminated after statistical controls for a number of health measures, suggesting that the association between cognitive function and survival is robust and can only in part be attributed to health factors.
A second set of analyses addressed the terminal decline hypothesis. Surviving participants were re-contacted and re-interviewed in 1997 and 1999. A total of 984 individuals participated in all three waves. Consistent with the terminal decline hypothesis, there was evidence that decline in cognitive function was more pronounced among the deceased when compared to the survivors. However, a history of cognitive decline did not predict mortality above and beyond the current level of cognitive functioning.