Effects of Statin Therapy on Glycemic Control and Associated Factors Among Type 2 Diabetes Mellitus Patients in Northeastern Tanzania: A Retrospective Cohort Study

Abstract

Introduction: Statins have been implicated in poor glycemic control among patients with diabetes mellitus (DM), prompting the US Food and Drug Administration (FDA) to update warning labels on all statins to reflect the risk of increased blood glucose levels. However, few studies from sub-Saharan Africa have assessed this concern. This study investigated the effects of statins on glycemic control among patients with Type 2 diabetes mellitus (T2DM) in Kilimanjaro, northeastern Tanzania. Materials and Methods: This was a hospital-based retrospective cohort study evaluating changes in glycated hemoglobin (HbA_1c) at 1-3, 7-12, and 19-24 months, as the primary outcome, comparing statin users and nonusers among T2DM patients attending DM clinic at Kilimanjaro Christian Medical Centre in Tanzania. Binomial regression models were fitted to calculate adjusted risk ratios for independent predictors of a ≥ 0.2% rise in HbA_1c, with statistical significance set at p < 0.05. Results: Out of 122 patients, 51 (41.8%) were on statin therapy. Among these, 46 (90.2%) were prescribed atorvastatin. Statin users had an increase of mean HbA_1c from 10.6% ± 2.7% at baseline compared to 11.6% ± 2.8% at 1-3 months (p = 0.114), followed by a decrease to 10.1% ± 2.2% at 7-12 months (p = 1.0), and 10.0% ± 2.5% at 19-24 months (p = 1.0). However, atorvastatin users (n = 46) had a significant increase of mean HbA_1c from 10.7% ± 2.8% at baseline compared to 11.9% ± 2.7% at 1-3 months (p = 0.04). In contrast, nonstatin users had a consistent and significant decrease in HbA_1c from 11.3% ± 2.8% at baseline compared to 9.7% ± 2.2% at 1-3 months (p = 0.001), to 9.7% ± 2.6% at 7-12 months (p = 0.011), and to 9.3% ± 2.2% at 19-24 months (p = 0.001). Conclusion: Statin therapy among patients with T2DM was associated with short-lived worsening of glycemic control at 1-3 months posttherapy.

Keywords: Tanzania; Type 2 diabetes mellitus; dyslipidemia; glycated hemoglobin (HbA1c); glycemic control; statins.

Figure 1

Flow chart for selection of study participant.

Figure 2

Demonstrating the change of the mean HbA_1c for statin users (red line) and nonusers (blue line) over time, at 1–3 months, statin users had an increase of HbA_1c of + 0.97% compared to nonusers who had a reduction of − 1.58%, there existed significant mean difference (MD) of 2.56% (95% CI: 3.59–1.53; p < 0.001). Nonstatin users had significant and sustained decline in HbA_1c from baseline compared to 1–3, 7–12, and 19–24 months (p < 0.05).

Figure 3

Effect of statins on glycemic control over time: The blue line shows patients on atorvastatin, with a significant mean HbA_1c increase from baseline compared to 1–3 months (p = 0.04). The red line rosuvastatin group shows no significant reduction from baseline to 1–3 months (p = 1.0). The green line (nonstatin users) shows a significant decrease of HbA_1c from baseline compared to 1–3 (p < 0.001), 7–12 (p = 0.001), and 19–24 months (p < 0.001).

Figure 4

Stratified the cohort into two groups: statin users and nonusers, to observe proportion of a 0.2% change in HbA_1c. (a) Statin user had higher risk for ≥ 0.2% rise of the mean HbA_1c (blue bar) at 1–3 months (p < 0.001). (b) Statin users had no significant risk for ≥ 0.2% rise of the mean HbA_1c (blue bar) at 7–12 months (p = 0.52).