Does psychological distress predict disability?

STUDY OBJECTIVE: To evaluate psychological distress as a predictor of disability due to common chronic disorders. STUDY POPULATION AND METHODS: A 10-year follow-up study was carried out among a representative cohort (N = 8655) of 18-64 year old Finnish farmers, who had participated in a health survey in 1979 and were able to work at baseline. A record linkage with the nationwide register of the Social Insurance Institution was made to identify disability pensions granted between 1980 and 1990 in the cohort. The medical certificates of 1004 (11.6%) prematurely retired farmers were reviewed to confirm and classify disabling conditions. A sum score based on self-reports of 11 symptoms at the baseline was used as a measure of psychological distress. RESULTS: After adjustment for age, sex, smoking and body mass index, the cause-specific relative risks (RR) (95% confidence intervals CI]) of disability in the highest quartile of the psychological distress score as compared with the lowest quartile were for myocardial infarction 2.34 (95% CI: 1.17-4.69), for depression 2.50 (95% CI: 1.09-5.72), for neck-shoulder disorders 1.98 (95% CI: 1.26-3.11), for unspecified low-back disorders 1.76 (95% CI: 1.24-2.49), for knee osteoarthritis 1.55 (95% CI: 0.91-2.63) and for trip osteoarthritis 0.89 (95% CI: 0.42-1.85). The corresponding RR for overall disability was 1.76 (95% CI: 1.44-2.14) in the highest quartile of psychological distress score as compared with the lowest quartile. CONCLUSIONS: Psychological distress is an independent risk factor for disability. Its predictive significance varies between disorders leading to functional deterioration. The association mechanisms are likely to vary from one disorder to another.