Age-related changes of the work ability construct and its relations to cognitive functioning in the older worker : a 16-year follow-up study

The aim was to find out age-related changes in the Work Ability Index (WAI) and cognitive functions as well as their cross-sectional and longitudinal relations. The data are based on the follow-up study of municipal employees which begun in 1981 when subjects' (N=6257) age-range varied between 44 and 58 years. The first dataset consists of those who replied to the questionnaires in 1981-1997, and remained at work until 1992 (n=717). The second consists of those who attended the laboratory tests and were occupationally active in 1981-1985 (n=68). It was expected that both the WAI and cognitive functions decrease during the 11 years, the changes being greater in the WAI than in cognitive functions, and that the changes in the WAI are more strongly correlated with self-rated than with measured cognitive functions. The methods included the WAI and five tests from the WAIS (Similarities, Block Design, Digit Symbol, Digit Span, and Picture Completion). Also self-ratings concerning reaction capacity, memory and sense of comprehension were used. The WAI decreased with ageing from 1981 to 1992, among men and women, and in all types of work. Also WAIS scores decreased from 1985 to 1997 with the exception of the Digit Span. The WAIS scores were highest in the mental work group. The important replicated finding was that the WAI began to decline in late middleage, but the decrease of WAIS scores started later and was clearly slower among those who were still working and especially doing mental work. The objective cognitive changes supported weakly the decline hypothesis. Self-rated cognitive functions partly improved during the follow-up and correlated higher with WAI than the test scores. The findings showed a mutual interaction between measured cognitive functioning and WAI as predicted. The crosslagged correlations between WAI and SCF were lower than expected. The physical and mixed types of work were detrimental for cognitive functioning and WAI. To keep cognitive functioning and the WAI high, the work should include characteristics typical of mental work.