Work ability as a determinant of old age disability severity: evidence from the 28-year Finnish Longitudinal Study on Municipal Employees.

BACKGROUND AND AIMS Lower occupational class correlates with a higher disability risk later in life. However, it is not clear whether the demands made by mental and physical work relative to individual resources in midlife predict well-being in old age. This study investigated prospectively whether work ability in midlife predicts disability severity in activities of everyday living in old age. METHODS Data come from the population-based 28-year follow-up called Finnish Longitudinal Study of Municipal Employees. A total of 2879 occupationally active persons aged 44-58 years answered a questionnaire on work ability at baseline in 1981 and activities of daily living in 2009. At baseline, perceived work ability relative to lifetime best was categorized into excellent, moderate, and poor work ability. At follow-up, disability scales were constructed based on the severity and frequency of difficulties reported in self-care activities of daily living (ADL) and instrumental activities of daily living (IADL). RESULTS There was a graded prevalence of ADL and IADL disability severity, according to excellent, moderate and poor midlife work ability (p<0.001). Employees with moderate midlife work ability had an 11 to 20% higher mean ADL or IADL disability severity score, compared with those with excellent midlife work ability (reference), incidence rate ratios (IRR) ranging from 1.11 (95% CI 1.01-1.22) to 1.20 (95% CI 1.10-1.30). Those with poor midlife work ability had a mean ADL or IADL disability severity score 27 to 38% higher than the referent, IRRs ranging from 1.27 (95% CI 1.09-1.47) to 1.38 (95% CI 1.25-1.53). Adjusting for socio-economics, lifestyle factors and chronic diseases only slightly attenuated the associations. CONCLUSIONS Work ability, an indicator of the de- mands made by mental and physical work relative to individuals' mental and physical resources, predicted disability severity 28 years later among middle-aged municipal employees.