Vitamin B12 and folate concentrations in recent-onset type 2 diabetes and the effect of metformin treatment.

CONTEXT: Vitamin B12 and folate deficiency are not only linked to hematological, neurological and cardiovascular diseases, but also associate with insulin resistance. Metformin can decrease vitamin B12 and folate concentrations. OBJECTIVE: To examine (i) effects of short-term metformin treatment on serum holotranscobalamin (holoTC) and folate and (ii) their association with insulin sensitivity in recent-onset type 2 diabetes. DESIGN: This cross-sectional analysis comprised patients (known disease duration <12 months) on metformin monotherapy (MET, n=123, 81 males, 53+/-12 years) or non-pharmacological treatment (NPT, n=126, 77 males, 54+/-11 years) of the German Diabetes Study. MAIN OUTCOME MEASURES: HoloTC (ELISA), cobalamin and folate (electrochemiluminescence); beta-cell function and whole-body insulin sensitivity, measured during fasting (HOMA-B, HOMA-IR) and intravenous glucose tolerance tests (IVGTT) combined with hyperinsulinemic-euglycemic clamp tests. RESULTS: HoloTC (105.4 [82.4, 128.3] vs. 97 [79.7, 121.9] pmol/L) and folate concentrations (13.4 [9.3, 19.3] vs. 12.7 [9.3, 22.0] nmol/L) were similar in both groups. Overall, holoTC neither associated with fasting nor glucose-stimulated beta-cell function and insulin-stimulated glucose disposal. Cobalamin measurements yielded similar results in representative subgroups. In NPT but not MET, folate levels were inversely correlated with HOMA-IR (r=-0.239, P=0.007). Folate levels neither related to insulin sensitivity nor insulin secretion in the whole cohort and in each group separately after adjustment for age, BMI and sex. CONCLUSIONS: Metformin does not affect circulating holoTC and folate concentrations in recent-onset type 2 diabetes, rendering monitoring of vitamin B12 and folate dispensable at least during the first 6 months after diagnosis or initiation of metformin.