Serum bicarbonate is an independent predictor of all-cause mortality in healthy subjects and of incident coronary heart disease in subjects with diabetes. In vivo and in vitro studies suggest that acid-base status may influence insulin resistance. We set out to determine whether there is an independent association between serum bicarbonate and insulin resistance in community-dwelling patients with type 2 diabetes.
The Fremantle Diabetes Study Phase II recruited a representative sample of patients with diabetes living in a post-code defined area surrounding Fremantle in Western Australia. We studied those patients with type 2 diabetes treated with diet or oral hypoglycaemic therapy only. Measurement of standard biochemical tests in fasting samples was carried out in an accredited laboratory using a Cobas Integra 800 analyser (Roche Diagnostics Australia). Serum insulin was measured in samples stored at -80°C using a Roche E170 analyser (Roche). Insulin resistance was assessed from glucose and insulin using the HOMA-2 algorithm (http://www.dtu.ox.ac.uk/homacalculator/).
There were 1190 participants with complete data. Their mean±SD age was 66±12 y and 51% were male. Their median [inter-quartile range] duration of diabetes was 6 [2-14] y and HbA1c was 6.6 [6.1 – 7.4]%.
Serum bicarbonate was significantly correlated with HOMA-2 IR (rS=-0.14; P < 0.001). In multivariable analysis adjusted for eGFR <60 mL/min/1.73m2, diuretic use, age at diagnosis, Charlson comorbidity index ≥3, smoking status and diastolic blood pressure, serum bicarbonate remained significantly associated with ln(HOMA-2 IR) (ß=-0.056, P<0.001).
Insulin resistance is independently and inversely associated with serum bicarbonate in this cohort of patients with type 2 diabetes. Our results are consistent with studies suggesting an association between these variables. Measures that improve a patient’s acid-base status may reduce the impact of insulin resistance on cardiovascular risk.