High l-carnitine concentrations do not prevent late diabetic complications in type 1 and 2 diabetic patients

Increased intake of l-carnitine, a cofactor in cellular energy metabolism, is recommended for diabetic patients with late complications. However, its clinical benefits remain controversial. We hypothesized that patients with low l-carnitine levels would have an increased rate of diabetic complications. To test this hypothesis, we evaluated the relationship of l-carnitine concentrations in blood with the prevalence and severity of late diabetic complications in type 1 and 2 diabetic patients. Human blood samples were collected from 93 and 87 patients diagnosed as having type 1 or type 2 diabetes, respectively, and 122 nondiabetic individuals. The determination of free l-carnitine concentrations in whole blood lysates was performed using ultra-performance liquid chromatography with tandem mass spectrometry. In diabetic patients, diabetic complications such as neuropathy, retinopathy, nephropathy, or hypertension were recorded. The average l-carnitine concentration in the blood of control subjects was 33 ± 8 nmol/mL, which was not significantly different from subgroups of patients with type 1 (32 ± 10 nmol/mL) or type 2 diabetes (36 ± 11 nmol/mL). Patients with low (<20 nmol/mL) l-carnitine levels did not have increased occurrences of late diabetic complications. In addition, patient subgroups with higher l-carnitine concentrations did not have decreased prevalence of late diabetic complications. Our results provide evidence that higher l-carnitine concentrations do not prevent late diabetic complications in type 1 and 2 diabetic patients.