Cognitive Function of Centenarians and Its Influence on Longevity
Gondo, Yasuyuki, Poon, Leonard W., Annual Review of Gerontology & Geriatrics
High cognitive function has been asserted to be an important contributor to longevity in general and especially in extreme longevity. The goals of this chapter are to (a) examine evidence for this assertion in normal and pathological aging, (b) identify confounding and not well understood issues, and (c) suggest future research directions relating to causal factors of cognition on longevity.
REVIEW OF SUPPORTIVE EVIDENCE
Impact Among the General Population
The Terman Cohort Study, which examined the life course of intellectually gifted individuals, addressed the relationship between individual differences in cognitive function and mortality (Friedman & Markey 2003). At the beginning of the study (1921), researchers recruited 1,528 younger people with IQs of 135 and higher. These individuals were followed 7 decades until 1991. Total mortality rates of these gifted individuals were lower than those of the general U.S. population born at the same time.
Similarly, a recent series of studies that utilized intelligence test data collected more than 50 years ago reported positive relationships between childhood intelligence and mortality in middle and very old age (Batty, Deary, & Macintyre, 2006; Deary, Bastin, et al., 2006; Hart et al., 2005; Shenkin, Starr, & Deary, 2004; Whalley & Deary, 2001; Whalley et al, 2000). Data came from the Scottish Mental Survey of 11-year-old children performed in 1932. The researchers linked these test scores with public morbidity and mortality data and found that a higher test score in childhood was associated with longer survival.
A study of nuns also addressed the relationship between individual differences in cognitive function and mortality (Snowdon, Greiner, Kemper, & Nanayakkara, 1999). The researchers analyzed linguistic ability from the participants' autobiographies written in their younger ages (18-32 years old). Two scores of linguistic ability-grammatical complexity and idea densitywere analyzed to examine the association between cognitive performances and mortality The results showed that idea density had a negative association with the risk of mortality Individuals with performance in the lowest quartile had a 7-year shorter life span than the higher performance group.
Bosworth and Siegler (2002) reviewed nine studies that evaluated the relationship between terminal decline of cognitive function and death. Although they did not find a consistent relationship, they did find that the level of cognitive function is predictive of mortality Recent statistically sophisticated analyses with representative-sample longitudinal studies reported the same pattern (Ghisletta, McArdle, & Lindenberger, 2006; Rabbitt, Lunn, & Wong, 2006). What causes the association between cognitive ability and mortality in elders? Medical condition and vitality decline are strong candidates. Hassing and colleagues (2002) followed 446 participants aged 80 to 98 for 6 years and found that participants with a shorter remaining life span showed lower cognitive ability in the baseline survey However, this association was attenuated after medical conditions such as stroke and cardiovascular disease were considered. The lower cognitive ability associated with death may be triggered by a decline of physical function or vitality.
Impact Among Centenarians
Six centenarian studies addressed the impact of cognition on longevity (Gondo et al., 2006; Hagberg, 2006; Kliegel & Sliwinski, 2004; Poon et al., 2000; Samuelsson et al., 1997; Shimizu, Hirose, Arai, Gondo, & Wakida, 2001). The French centenarian study surveyed 800 centenarians and followed them for 8 years until 99% had died. Cognitive impairment measured by the short portable mental status questionnaire, a test similar to the Mini Mental State Examination (MMSE), significantly predicted survivorship as well as did residential condition, health status, activities of daily living (ADL), and independent activities of daily living (IADL). …