Background: Type 2 diabetes (T2D) causes significant health and economic burden. In addition to comorbidities there are also coexisting diseases linked to obesity, lifestyle and T2D. The aim of this study was to examine the effect of T2D and T2D-coexisting diseases on health-related quality of life (HRQoL) in the Finnish population and whether it is T2D or the coexisting diseases that have the largest impact on HRQoL.

Methods: The study was based on a national cross-sectional population survey (n=5305). Respondents' HRQoL was measured using the EQ-5D-5L instrument. Our study included diabetic respondents treated with non-insulin medications (NI-T2D) with or without insulin and non-diabetic respondents, whereas diabetic respondents not taking any anti-diabetic medications or treated with insulin alone were excluded. A crosswalk algorithm was used to convert EQ-5D-5L index scores into EQ-5D-3L index scores as a sensitivity analysis. A two-part model was used to examine the association between T2D and coexisting diseases and HRQoL.

Results: The unadjusted mean (SD) EQ-5D-5L index scores for non-diabetics (n=4856) was 0.90 (0.13) and 0.85 (0.16) for respondents with NI-T2D (n=449). With adjustment for demographic factors, the difference in EQ-5D-5L index scores was 0.036 (95% CI 0.023-0.050). After adjusting for the number of coexisting diseases, the EQ-5D-5L index scores among respondents with NI-T2D and three or more coexisting diseases were lower when compared to all non-diabetics but not when compared to non-diabetics with similar number of coexisting diseases. The number of T2D-coexisting diseases had a larger effect on EQ-5D-5L index scores in younger age groups (20 and 40years old).

Conclusions: Lower EQ-5D-5L index score is associated with NI-T2D when compared to non-diabetic respondents. When compared to non-diabetics, the disutility associated with NI-T2D increases as more coexisting diseases appear. The disutility effect of coexisting diseases was equally large in non-diabetics and respondents with NI-T2D. Thus, public health interventions targeting the prevention of both T2D and its coexisting diseases have potential to have significant benefits also in terms of HRQoL.