High Salt Intake Augments Blood Pressure Responses During Submaximal Aerobic Exercise

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); VO(2)peak =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% VO2peak. 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=Delta 30.0 +/- 16.3 versus Na+=Delta 38.3 +/- 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.