Cognitive impairment and health-related quality of life amongst older Australians: evidence from a longitudinal investigation

Introduction: Australia's population is steadily growing older, with older persons expected to make up over 20% of the population by 2066. Ageing is strongly associated with a significant drop in cognitive ability, ranging from mild cognitive impairment to severe cognitive impairment (dementia). This study examined the association between cognitive impairment and health-related quality of life (HRQoL) in older Australians.

Methods: Two waves of longitudinal data from the nationally representative Household, Income and Labour Dynamics in Australia (HILDA) survey were utilised, with the age cut-off for older Australians defined as above 50. The final analysis included 10,737 person-year observations from 6892 unique individuals between 2012 and 2016. This study utilised the Backwards Digit Span (BDS) test and Symbol Digit Modalities test (SDMT) to assess cognitive function. HRQoL was measured using the physical and mental component summary scores of the SF-36 Health Survey (PCS and MCS). Additionally, HRQoL was measured using health state utility values (SF-6D score). A longitudinal random-effects GLS regression model was used to analyse the association between cognitive impairment and HRQoL.

Results: This study found that approximately 89% of Australian adults aged 50 or older had no cognitive impairment, 10.16% had moderate cognitive impairment, and 0.72% had severe cognitive impairment. This study also found that moderate and severe cognitive impairment were both negatively associated with HRQoL. Older Australians with moderate cognitive impairment scored worse on the PCS (β = - 1.765, SE = 0.317), MCS (β = - 1.612, SE = 0.326), and SF-6D (β = - 0.024, SE = 0.004) than peers without cognitive impairment given other covariates reference categories remain constant. Older adults experiencing severe cognitive had lower PCS (β = - 3.560, SE = 1.103), and SF-6D (β = - 0.034, SE = 0.012) scores compared to their counterparts with no cognitive impairment given other covariates reference categories remain constant.

Conclusion: We found evidence that HRQoL is negatively associated with cognitive impairment. Our findings will be beneficial for the future cost-effectiveness intervention targeted at reducing cognitive impairment since it provides information on the disutility associated with moderate and severe cognitive impairment.