Cognitive abilities in later life and the onset of physical frailty: the Lothian Birth Cohort 1936

OBJECTIVES: To investigate whether poorer cognitive ability is a risk factor for the development of physical frailty, and whether this risk varies by cognitive domain. DESIGN: Prospective longitudinal study with six-year follow-up.SETTING: Edinburgh, Scotland.PARTICIPANTS: 594 members of the Lothian Birth Cohort 1936.MEASUREMENTS: Frailty was assessed at ages 70 and 76 using the Fried criteria. Cognitive functions were assessed at ages 70, 73, and 76. Factor score estimates were derived for baseline level of and change in four cognitive domains: visuospatial ability, memory, processing speed, and crystallized cognitive ability. RESULTS: Higher baseline levels of processing speed, memory, visuospatial ability and crystallized ability derived from ages 70, 73 and 76, and less decline in speed, memory and crystallized ability were associated with a reduced risk of becoming physically frail by age 76. When all cognitive domains were modelled together, processing speed was only domain associated with frailty risk: for a standard deviation increment in initial level of processing speed, the relative risk for frailty (RR) (95% confidence interval (CI)) was 0.53 (0.33, 0.85), after adjustment for age, sex, baseline frailty status, social class, depressive symptoms, number of chronic physical diseases, levels of inflammatory biomarkers, and other cognitive factor score estimates; for a SD increment in processing speed change (i.e. less decline) the RR (95% CI) was 0.26 (0.16, 0.42). When we conducted additional analyses using a single test of processing speed that did not require fast motor responses—Inspection Time—results were similar.CONCLUSIONS: The speed with which older people process information and the rate at which this declines over time may be an important indicator of the risk of physical frailty.