Low-Sodium DASH reduces oxidative stress and improves vascular function in salt-sensitive humans

Abstract

Salt induces oxidative stress in salt-sensitive (SS) animals and man. It is not known whether in SS subjects the low-sodium dietary approaches to stop hypertension (LS-DASH) reduces oxidative stress more than DASH, which is high in antioxidants. To assess the effects of DASH and LS-DASH on oxidative stress, 19 volunteers were studied after 3 weeks of a standardized usual low fruits and vegetables diet (ULFV), followed by 3 weeks on DASH (both diets approximately 120 mmol Na(+) per day), then 3 weeks on LS-DASH (60 mmol Na(+) per day). SS was defined as systolic blood pressure >or=5 mm Hg lower on LS-DASH than DASH. In SS subjects (N=9), systolic blood pressure was lower on LS-DASH (111.0+/-2.0 mm Hg) than DASH (118.0+/-2.2, P<0.01) and ULFV (122.3+/-2.7, P=0.002). In salt-resistant (SR) volunteers (N=10), systolic blood pressure was lower on DASH (113.0+/-1.6) than ULFV (119.0+/-1.8, P<0.05) but not LS-DASH (115.7+/-1.8). Urine F2-isoprostanes, a marker of oxidative stress, were lower in SS subjects on LS-DASH (1.69+/-0.24) than ULFV (3.09+/-0.50, P<0.05) and marginally lower than DASH (2.46+/-0.44, P<0.20). F2-isoprostanes were not different among the three diets in SR volunteers (2.18+/-0.29, 2.06+/-0.29, 2.27+/-0.53, respectively). Aortic augmentation index, a measure of vascular stiffness, was lower in SS subjects on LS-DASH than either DASH or ULFV, and lower on DASH than ULFV in SR volunteers. In SS but not SR subjects, LS-DASH is associated with lower values for F2-isoprostanes and the aortic augmentation index. The results suggest that LS-DASH decreases oxidative stress, improves vascular function and lowers blood pressure in SS but not SR volunteers.

Figure 1

Peripheral (brachial, cuff [left side]) and estimated central (right side) systolic (SBP [top]) and diastolic blood pressures (DBP [bottom]) are provided for salt sensitive [●SS] and salt resistant [▲SR] subjects on the three dietary periods. Values reflect the means and standard errors of multiple baseline, supine readings after three weeks on each diet. ULFV = usual diet low in fruits and vegetables; DASH = high fruits and vegetables Dietary Approaches to Stop Hypertension. LS-DASH = low-sodium, high fruits and vegetables DASH. * p<0.05 DASH vs ULFV in SR; ++ p<0.01 LS-DASH vs ULFV in SS; # p<0.05 LS-DASH vs DASH in SS.

Figure 2

Urine F2-isoprostane values are shown for the salt sensitive [●SS] and salt resistant [▲SR] subjects on the three dietary periods. Urine isoprostanes were lower on LS-DASH than ULFV in SS subjects. + p<0.05 LS-DASH vs ULFV in SS.

Figure 3

The aortic (central) augmentation index (AIx [upper panel]) was lower on LS-DASH than ULFV and DASH in SS subjects [●SS]. Among SR subjects [▲SR], AIx was lower on DASH than ULFV. Small artery elasticity (lower panel) was higher on LS-DASH than ULFV in SS subjects. * p<0.05 DASH vs ULFV in SR; ++ p<0.01 LS DASH vs ULFV, ##, p<0.01 LS-DASH vs DASH; α p<0.05 SS vs SR on ULFV; β p<0.05 SS vs SR on DASH.