To the Editor: This letter comments on the article ‘Type 2 diabetes mellitus worsens arterial stiffness in hypertensive patients through endothelial dysfunction’ by Bruno et al [1].

The role of endothelial dysfunction in determining aortic stiffness in individuals with hypertension who also had type 2 diabetes, but not in people without diabetes, reported in this paper, provides a mechanism likely to contribute to the increases in incidence, and mortality from, cardiovascular disease—well known problems in those with type 2 diabetes, particularly since they also have a higher incidence of hypertension than do non-diabetic individuals. The identification of factors that might be able to reduce endothelial dysfunction is, therefore, of great potential practical importance, especially for those with both type 2 diabetes and hypertension. The association of endothelial dysfunction with arterial stiffness reported in these hypertensive diabetic patients was not accounted for by obesity, and thus some other factor remains to be identified. Review of the literature suggests that increased type 2 diabetes risk is associated with hypovitaminosis D [2], the latter being itself associated with vascular endothelial dysfunction [3]. Furthermore, several randomised controlled trials of vitamin D supplementation in those with marked vitamin D deficiency have shown improvements in endothelial function, in younger rather than older people, independent of concomitant reductions in blood pressure; in some cases these have involved improvement in both endothelial markers of vascular dysfunction and in glycaemic status and lipid profiles [4, 5]. It would be of great interest, therefore, if the authors have measurements of vitamin D status (serum 25-hydroxyvitamin D [25(OH)D] concentration) available, or samples that could be assayed for 25(OH)D, to see what the inclusion of this variable in their analyses might show. This is an important issue since, if vitamin D status proves to be a predictor of vascular function in the cohort with type 2 diabetes and hypertension [1], then vitamin D supplementation would need to be examined in appropriate trials as a potential adjunctive treatment for such patients.