Multimorbidity and  health-related quality of life among people 55 years and up: results of a longitudinal study in New Zealand

Background: This study aimed to examine the association of Health-Related Quality of Life (HRQOL) and multimorbidity (MM) and its correlates over time in New Zealand. Methods: People aged 55 years and over were invited to participate in a nationally representative population-based longitudinal study in 2006 and followed up biennially until 2016. Generalized Estimating Equations (GEE) with an exchangeable correlation matrix and robust standard errors adjusted for both time-constant and time-varying factors using baseline and five subsequent waves of data were used, to compare a range of factors related to changes in MM and HRQOL. Results: Of 2632 participants at baseline, 957 of the participants were classified as “MM participants”; 570 had two, and the rest had three chronic conditions. The results of the GEE regression models demonstrated that SF12-PCS decreased over time, and there was a significant difference in SF12-PCS between MM and Non-MM participants. Having MM was negatively associated with HRQOL-PCS [-3.00 (95 %CI -3.60, -2.49); p <0.001)]. Although the results showed an increase in SF12-MCS over time, the score of the mental dimension of HRQOL was lower among MM participants compared to Non-MM participants [-2.60, 95 %CI -3.09, -2.11]. Conclusions: According to this longitudinal study, there is an inverse association between MM and one of the most important health outcomes; HRQOL, in older adults.