['Vascular endothelial dysfunction is involved in macrovascular disease progression in type 2 diabetes mellitus (T2DM). We reported previously that blood glucose fluctuations, as evaluated by continuous glucose monitoring (CGM), correlate with vascular endothelial function, serving as a marker of vascular endothelial function. However, the use of CGM is limited, suggesting the need for another marker of vascular endothelial function. Here, we investigated the relationship between vascular endothelial dysfunction and blood levels of 1,5-anhydro-D-glucitol (1,5-AG), a marker of both postprandial hyperglycemia and fluctuations in blood glucose.', 'In 32 inpatients with T2DM and HbA1c less than 8.0%, the reactive hyperemia index (RHI), an index of vascular endothelial function, was determined by peripheral arterial tonometry. The relationships between RHI and 1,5-AG, blood glucose, lipid metabolism markers, and blood pressure, were examined.', 'There was a strong correlation between 1,5-AG and natural logarithmic-scaled RHI (L_RHI) (r\u2009=\u20090.55; P\u2009=\u20090.001). However, there was no correlation between L_RHI and HbA1c, fasting blood glucose, IRI, LDL-C, HDL-C, TG, systolic blood pressure, or diastolic blood pressure. Multivariate analysis identified blood 1,5-AG levels to be the only significant and independent determinant of L_RHI.'] Are low levels of 1,5-anhydro-D-glucitol associated with vascular endothelial dysfunction in type 2 diabetes?