Dietary NaCl Restriction Deteriorates Oral Glucose Tolerance in Hypertensive Patients With Impairment of Glucose Tolerance

Abstract

This study investigated whether the change of glycemic response to oral glucose loading with an increase of dietary NaCl intake is different between salt-sensitive and salt-resistant groups, or whether it is related to glucose tolerance on a low NaCl diet independent of salt sensitivity. The plasma glucose and insulin response to 75 g oral glucose intake was assessed on low (34 mmol/day) and high (342 mmol/day) NaCl diets in 31 patients with essential hypertension, and the area under the curve for both variables (AUCglu and AUCins) was calculated. The data on the high NaCl diet were corrected for change in hematocrit. The percentage change in systolic, diastolic, and mean blood pressure between the two diets was defined as the salt sensitivity index (SSI) for systolic blood pressure (SSISBP), diastolic blood pressure (SSIDBP), and mean blood pressure (SSIMBP), respectively. The mean values of both AUCglu and AUCins decreased significantly with increase of NaCl intake; however, there was no significant correlation between SSI (SSISBP, SSIDBP, or SSIMBP) and the percentage changes in AUCglu and AUCins. Meanwhile, the percentage changes in AUCglu and AUCins significantly correlated with the respective values of AUCglu and AUCins on the low NaCl diet. These results suggest that extreme NaCl restriction may deteriorate glucose metabolism in hypertensive patients, especially in those with diabetes mellitus or impaired glucose tolerance.

Increased insulin resistance in salt sensitive essential hypertension

“…Several studies [5][6][7][8][9][10][11][12][13][14][15] have addressed the issue of the possible relationship between salt sensitivity and both insulin resistance and other glucose metabolic parameters, with some controversial results. In normotensive subjects, Sharma et al 6,7 found a direct relationship between salt sensitivity and insulin response to an oral glucose tolerance test, 6 a finding confirmed 2 years after measuring insulin sensitivity by the insulin suppression test.…”

“…Journal of Human Hypertension (2001) 15, 481-485 jects. 5,[9][10][11][12][13][14][15] Some authors have found higher degrees of insulin resistance in salt sensitive hypertensive patients, 9,10 whereas others have found no relationship in hypertensives, 11 obese 12 or normotensives. 13 Finally, two reports in hypertensive patients have found an increase in insulin sensitivity in salt sensitive hypertensive subjects.…”

Correlation of sodium-related factors with insulin sensitivity in young, lean, male offspring of hypertensive and normotensive subjects

“…Some investigators have indicated that moderate dietary sodium restriction aggravates insulin sensitivity; 11,12 others have suggested that salt loading exacerbates insulin resistance. 25 Dietary salt restriction increases resistance to the vasodilating effects of insulin in young normotensive and hypertensive subjects.…”

“…10 On the contrary, salt restriction aggravates insulin resistance in normotensive subjects. 11,12 There have been few studies dealing with the relationship between sodium-related factors under the condition of unrestricted diets and insulin resistance in young lean normotensive subjects in relation to the genetical predispositions for the development of essential hypertension.…”

The Antinatriuretic Effect of Insulin: An Unappreciated Mechanism for Hypertension Associated with Insulin Resistance?

“…However, in contrast to the above findings, other studies did not report significant differences in the levels of insulin resistance between salt-sensitive and salt-resistant individuals [60,61,62], while others found a reverse relation between insulin resistance and salt sensitivity [63, 64], or significantly lower levels of insulin resistance in salt-sensitive compared to salt-resistant hypertensives [63, 65]. …”