High Salt Intake Augments Blood Pressure Responses During Submaximal Aerobic Exercise

Abstract

Background High sodium (Na⁺) intake is a widespread cardiovascular disease risk factor. High Na⁺ intake impairs endothelial function and exaggerates sympathetic reflexes, which may augment exercising blood pressure (BP) responses. Therefore, this study examined the influence of high dietary Na⁺ on BP responses during submaximal aerobic exercise. Methods and Results Twenty adults (8F/12M, age=24±4 years; body mass index 23.0±0.6 kg·m^-2; VO₂peak=39.7±9.8 mL·min^-1·kg^-1; systolic BP=111±10 mm Hg; diastolic BP=64±8 mm Hg) participated in this randomized, double-blind, placebo-controlled crossover study. Total Na⁺ intake was manipulated via ingestion of capsules containing either a placebo (dextrose) or table salt (3900 mg Na⁺/day) for 10 days each, separated by ≥2 weeks. On day 10 of each intervention, endothelial function was assessed via flow-mediated dilation followed by BP measurement at rest and during 50 minutes of cycling at 60% VO_2peak. Throughout exercise, BP was assessed continuously via finger photoplethysmography and every 5 minutes via auscultation. Venous blood samples were collected at rest and during the final 10 minutes of exercise for assessment of norepinephrine. High Na⁺ intake increased urinary Na⁺ excretion (placebo=140±68 versus Na⁺=282±70 mmol·24H^-1; P<0.001) and reduced flow-mediated dilation (placebo=7.2±2.4 versus Na⁺=4.2±1.7%; P<0.001). Average exercising systolic BP was augmented following high Na⁺ (placebo=Δ30.0±16.3 versus Na⁺=Δ38.3±16.2 mm Hg; P=0.03) and correlated to the reduction in flow-mediated dilation (R=-0.71, P=0.002). Resting norepinephrine concentration was not different between conditions (P=0.82). Norepinephrine increased during exercise (P=0.002), but there was no Na⁺ effect (P=0.26). Conclusions High dietary Na⁺ augments BP responses during submaximal aerobic exercise, which may be mediated, in part, by impaired endothelial function.

Keywords: acute exercise; blood pressure; dietary sodium; exercise pressor reflex; flow‐mediated dilation.

Figure 1. Following 10 days of high sodium intake (filled bar), flow‐mediated dilation is significantly reduced compared with 10 day of habitual of sodium intake (open bar).

Data are presented as mean and individual data points.

Figure 2. Changes in (A and B) systolic (C and D) mean, and (E and F) diastolic blood pressure from baseline during submaximal aerobic exercise.

Following 10 days of habitual sodium intake (open circles) BP increase during aerobic exercise. However, following 10 days of high sodium intake (closed squares), systolic and mean blood pressure responses are augmented. Data are presented as mean±SD (A, C, and E) or mean and individual data points (B, D, and F).

Figure 3. The reductions in flow‐mediated dilation were negatively and significantly correlated to the increases in systolic blood pressure during submaximal aerobic exercise, such that individuals with the greatest reductions in flow‐mediated dilation had the largest increases in exercising systolic blood pressure.