Overall, genetically predicted higher l-carnitine was associated with higher triglycerides (effect size 0.04, 95% CI 0.02 to 0.05 per SD increase in genetically predicted l-carnitine) (Fig. 3), and nominally associated with lower HDL-cholesterol (− 0.02, 95% CI − 0.04 to − 0.01) (Fig. 3), Genetically predicted l-carnitine was nominally related to higher risk of diabetes (p = 0.04), but was not related to other glycemic traits (glucose, HbA1c or insulin). This evidence concerns the gene INS and diabetes mellitus.