Moderate dietary salt restriction increases vascular and systemic insulin resistance

Our recent studies have indicated that severe salt restriction aggravates v ascular insulin resistance in younger normotensive and hypertensive subject s. However, whether the extent of dietary salt restriction commonly advocat ed adversely affects vascular insulin resistance is unknown. To determine w hether moderate dietary salt restriction might affect vascular and systemic sensitivity to insulin, we studied eight subjects after 1 week of a normal sodium diet (235 mEq/day) and 1 week of a moderate salt restriction (75 me q/day). Systemic insulin resistance as assessed by the fasting plasma gluco se-to-insulin ratio was aggravated by dietary sodium restriction (normal so dium: 1.2 +/- 0.1 mmol/mIU; low sodium 0.6 +/- 0.1, P < .05). Salt restrict ion significantly reduced maximal insulin-mediated vasodilation (normal sod ium: 51% +/- 5% of maximum nitroglycerin-mediated response; low sodium: 28% +/- 6%, P < .01). In contrast, no alterations in nitroglycerin-mediated va sodilation nor phenylephrine-mediated vasoconstriction were noted. These st udies demonstrate that moderate salt restriction aggravates both systemic a nd vascular insulin resistance. This impairment of the vasodilating effect of insulin could be a factor attenuating the blood pressure lowering effect of a low sodium diet. (C) 1999 American Journal of Hypertension, Ltd.