Selenium is an essential trace element important to human health. Nonetheless, supra‐nutritional selenium intake is reported to be associated with insulin resistance and may therefore increase the risk of diabetes and disrupt endothelial function (ED), the initial step in atherosclerosis development. However, the underpinning molecular mechanisms are not clear. High selenium concentrations cause apoptosis in cancer cells through the induction of endoplasmic reticulum (ER) stress, a mechanism also involved in the pathogenesis of ED. Therefore, we hypothesised here that high selenium intake could cause ED through the activation of ER stress response.