Purpose: Previous studies have reported a positive association between poor health-related quality of life (HRQOL) and disability mainly in relation to the physical component of HRQOL. Given the mental component's responsivity to interventions, this study aimed to investigate whether the mental component of HRQOL independently predicted functional disability.
Methods: We targeted all residents aged ≥ 65 years in one municipality and analyzed 3858 men and 4475 women without disability at baseline (November 2016). HRQOL was measured using the physical component summary (PCS) and mental component summary (MCS) of the SF-8 Health Survey. At 3-year follow-up (October 2019), incident functional disability was measured, defined as a new certification according to the Japanese long-term care insurance system. Multivariable Poisson regression models stratified by gender were used to estimate adjusted cumulative incidence ratio (CIR) and 95% confidence interval (CI) for functional disability.
Results: Among both genders, there was a significant dose-response relationship between better MCS and lower risk of functional disability, independent of potential confounders including the PCS (P for trend = 0.026 in men and 0.003 in women). Compared with the worst MCS group, the CIRs (95% CIs) for functional disability in the second worst, the middle, the second best, and the best MCS quintile groups were 1.09 (0.80-1.48), 0.58 (0.40-0.85), 0.90 (0.59-1.37), and 0.70 (0.48-1.02) for men, and 0.76 (0.58-1.00), 0.62 (0.46-0.84), 0.73 (0.53-0.99), and 0.63 (0.48-0.85) for women, respectively.
Conclusion: The MCS is an independent predictor of functional disability among high-functioning older adults. This suggests that strategies focused on mental HRQOL are important for realizing a healthy, long-lived society.
Keywords: Community-dwelling older people; Functional disability; Health-related quality of life; Prospective study; SF-8.