The impact of depression diagnosis on diabetes and lifetime hyperglycaemia

Aims The aim of this study was to evaluate longitudinal associations between the mean and variability of HbA1c levels in individuals with type 2 diabetes (T2D) and major depressive disorder (MDD). Methods Individuals with T2D from the UK Biobank with linked primary care records were analysed. An HbA1c measurement within +/- 6-months of T2D diagnosis was taken as baseline, with subsequent HbA1c measurements used as the outcome in generalised least squares regression to evaluate longitudinal associations with a three-level MDD diagnosis variable (MDD controls, pre-T2D MDD cases and post-T2D MDD cases). Results Using 7,968 T2D individuals, we show that MDD has utility in explaining mean HbA1c levels (p=6.53E-08). This is attributable to MDD diagnosis interacting with baseline T2D medication (p=3.36E-04) and baseline HbA1c (p=2.66E-05), but not with time- when all else is equal, the temporal trend in expected HbA1c did not differ by MDD diagnosis. However, joint consideration with baseline T2D medication showed that each additional medication prescribed was associated with a +4 mmol/mol (2.5%) increase in expected HbA1c across follow up for post-T2D MDD cases, relative to pre-T2D MDD cases and MDD controls. Furthermore, variability in HbA1c increased across time for post-T2D MDD cases but decreased for MDD controls and pre-T2D MDD cases. Conclusions These findings suggest closer monitoring of individuals with both T2D and MDD is essential to improve their diabetic control, particularly for those who develop MDD after T2D diagnosis.