Universal drug coverage and income-related disparities in glycaemic control

Aims — To examine whether income-related disparities in glycaemic control decline after the age of 65 years, when publicly funded universal drug insurance is acquired.

Methods — We conducted a population-based cross-sectional study using linked administrative healthcare databases. Adults with diabetes, aged 40-89 years, with available HbA_1c data were included (N=716 297). Income was based on median neighbourhood household income. Multiple linear regression was used to test for effect modification of age ≥65 years on the relationship between income and HbA_1c.

Results — There was a significant inverse association between income and HbA_1c level. After adjusting for baseline factors, the effect of income on HbA_1c level was significantly greater for individuals aged < 65 years (mean difference HbA_1c for lowest vs highest income group +2.5 mmol/mol, 95% CI +2.3 to +2.7 [+0.23%, 95% CI 0.21 to 0.24]) than for those aged > 65 years (+1.2 mmol/mol, 95% CI +1.0 to +1.3 [+0.11%, 95% CI 0.10 to 0.12]; P<0.0001 for interaction).

Conclusions — Despite universal access to healthcare, people with diabetes on lower incomes had significantly worse glycaemic control compared with their counterparts on higher incomes. However, income gradients in glycaemic control were markedly reduced after the age of 65 years, possibly as a result of access to prescription drug coverage.