Elevation of fasting morning glucose relative to hemoglobin A1c in normoglycemic patients treated with niacin and with statins

BackgroundNiacin increases fasting glucose levels, and statins modestly increase the rate of new-onset diabetes. The clinical importance and mechanisms of these effects are not fully explored.ObjectiveOn the basis of anecdotal observations, we hypothesized that elevated morning fasting glucose may be accompanied by relatively normal hemoglobin A1c (HbA1c) in patients treated with niacin and other lipid-modifying drugs. We conducted a retrospective cohort analysis to test this hypothesis.MethodsThe Duke Lipid Clinic database (1994–2007) was screened for simultaneous determinations of fasting morning glucose and HbA1c, yielding 1483 data pairs among 554 subjects. Subjects with diabetes, by clinical diagnosis, medication, or any HbA1c ≥6.5%, or nondiabetes were analyzed separately. Repeated-measures linear regression featured glucose as dependent variable and included terms for HbA1c, drug(s), and their interaction.ResultsRegression lines for glucose on HbA1c had altered slopes in the presence of niacin and/or statin use in normoglycemic subjects. The corresponding interaction terms (drug and HbA1c) were significant (niacin P = .026, statin P = .013). Fibrate use had no effect (interaction P = .49). When modeled together, niacin and statin effects were independent. Regression curves in diabetic patients were not affected by lipid medications.ConclusionElevated fasting glucose may be accompanied by relatively normal HbA1c in niacin- and statin-treated patients. HbA1c reflects average daily glucose levels and is likely a better measure of the glycemic effect of lipid medications. Because our data were retrospective, confirmation from randomized trials is needed.