Effect of salt on insulin sensitivity differs according to gender and degree of salt sensitivity

The aim of the present study was to investigate the effect of salt intake on insulin sensitivity and the relation between salt sensitivity and insulin sensitivity in genetically hypertension-prone individuals. Twenty-eight healthy subjects (13 men and 15 women) with a family history of hypertension were examined at baseline, after 1 week of salt restriction (10 mmol/d), and after 1 week of salt loading (240 mmol/d). Insulin sensitivity was measured with the hyperinsulinemic euglycemic clamp after the low- and high-salt diets. Salt sensitivity was;defined as the difference in mean arterial blood pressure between the high-salt and the low-salt diets. There was no significant relationship between insulin sensitivity and salt sensitivity after either of the 2 diets. In the men, salt sensitivity was inversely related to plasma renin activity (r = -0.61, P = 0.03) and plasma aldosterone (r = -0.74, P = 0.004), whereas salt sensitivity in women was directly correlated with the salt-induced increase in body weight (r = 0.68, P = 0.005). In men, the high-salt diet induced a change in glucose disposal that was strongly correlated with the degree of salt sensitivity (r = 0.83, P = 0.0004), plasma renin activity (r = -0.82, P = 0.0006), and plasma aldosterone concentrations (r = -0.87, P = 0.00009) (eg, the greater the salt sensitivity and the lower the activity of the renin-angiotensin aldosterone system, the greater improvement in insulin sensitivity). No such relationships were observed in women. In conclusion, increased salt sensitivity and decreased activity of the renin-angiotensin-aldosterone system predict improved insulin sensitivity with high-salt intake compared with low-salt intake in men, suggesting an interaction among salt intake, salt sensitivity, the renin-angiotensin-aldosterone system, and insulin action.