Blood pressure responses to exercise during high dietary salt intake
Date
2019
Authors
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Publisher
University of Delaware
Abstract
Excess dietary sodium intake is a widespread cardiovascular disease risk factor. High dietary sodium intake expands plasma volume and increases sympathetic responses to stimuli in rodents. It remains unknown how high dietary sodium affects sympathetic and blood pressure (BP) responses to exercise in humans. PURPOSE: To examine the effects of increased dietary sodium intake on sympathetic and BP responses to exercise and post-exercise hypotension (PEH) following aerobic exercise. HYPOTHESIS: High dietary sodium intake will augment sympathetic and BP responses to isometric handgrip exercise. High dietary sodium intake will augment BP responses to submaximal aerobic exercise and attenuate PEH following aerobic exercise. METHODS: These hypotheses were tested using two experimental protocols. In the first protocol, participants increased their sodium intake via a controlled feeding study with diets containing recommended (2300 mg/day) and high (7000 mg/day) sodium. Diets were consumed in random order for 10 days each. On the tenth day, sympathetic and BP responses to isometric handgrip were recorded. In the second protocol, participants consumed a recommended (2300 mg Na+/day) sodium diet and took pills containing either salt (3900 mg Na+/day) or a placebo (dextrose). Participants consumed either salt or placebo for 10 days each in random order. On the tenth day, beat-to-beat BP was measured during one hour of submaximal aerobic exercise on an electronically-braked cycle ergometer. Following exercise, participants underwent one hour of in-lab beat-to-beat BP measurements. A subset of participants also underwent ambulatory BP monitoring for 24 hours after exercise. RESULTS: Controlled feeding increased urinary sodium excretion (n=25, recommended=95±9, high=243±15 mmol/24H, p<0.001). Sympathetic (n=14; burst frequency: recommended=10.6±2.7, high=11.1±2.6 bursts/min, p=0.83) and blood pressure (SBP: recommended=21.0±2.1, high=20.4±1.7 mmHg, p=0.79) responses were not different between diets. Salt pills increased urinary sodium excretion (n=20 placebo=136±16, salt=273±13 mmol/24H, p<0.001). BP responses during submaximal aerobic exercise were augmented (p<0.05) and PEH was attenuated (p<0.05). CONCLUSIONS: High dietary sodium increases BP responses to aerobic, but not isometric, exercise. Further, high dietary sodium attenuates PEH following acute submaximal aerobic exercise. These data indicate that high dietary sodium adversely affects BP responses to exercise and may reduce the beneficial effects of aerobic exercise for cardiovascular health.