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Eur J Appl Physiol. 2019 Sep;119(9):2105-2118. doi: 10.1007/s00421-019-04199-2. Epub 2019 Aug 3.

Impact of 3-day high and low dietary sodium intake on sodium status in response to exertional-heat stress: a double-blind randomized control trial.

Author information

1
Department of Nutrition, Dietetics and Food, Monash University, Level 1, 264 Ferntree Gully Road, Notting Hill, VIC, 3168, Australia. alan.mccubbin@monash.edu.
2
Department of Physiology, Monash University, Clayton, VIC, Australia.
3
Faculty of Health Sciences and Medicine, Bond University, Gold Coast, QLD, Australia.
4
Department of Nutrition, Dietetics and Food, Monash University, Level 1, 264 Ferntree Gully Road, Notting Hill, VIC, 3168, Australia.

Abstract

PURPOSE:

To determine the impact of altering dietary sodium intake for 3 days preceding exercise on sweat sodium concentration [Na+], and cardiovascular and thermoregulatory variables.

METHODS:

Fifteen male endurance athletes (runners n = 8, cyclists n = 7) consumed a low (LNa, 15 mg kg-1 day-1) or high (HNa, 100 mg kg-1 day-1) sodium diet, or their usual free-living diet [UDiet, 46 (37-56) mg kg-1 day-1] for 3 days in a double-blind, randomized cross-over design, collecting excreted urine (UNa) and refraining from exercise. On day 4, they completed 2 h running at 55% [Formula: see text]O2max or cycling at 55% maximum aerobic power in Tamb 35 °C. Pre- and post-exercise blood samples were collected, and sweat from five sites using absorbent patches along the exercise protocol.

RESULTS:

UNa on days 2-3 pre-exercise [mean (95% CI) LNa 16 (12-19) mg kg-1 day-1, UDiet 46 (37-56) mg kg-1 day-1, HNa 79 (72-85) mg kg-1 day-1; p < 0.001] and pre-exercise aldosterone [LNa 240 (193-286) mg kg-1 day-1, UDiet 170 (116-224) mg kg-1 day-1, HNa 141 (111-171) mg kg-1 day-1; p = 0.001] reflected sodium intake as expected. Pre-exercise total body water was greater following HNa compared to LNa (p < 0.05), but not UDiet. Estimated whole-body sweat [Na+] following UDiet was 10-11% higher than LNa and 10-12% lower than HNa (p < 0.001), and correlated with pre-exercise aldosterone (1st h r =  - 0.568, 2nd h r =  - 0.675; p < 0.01). Rectal temperature rose more quickly in LNa vs HNa (40-70 min; p < 0.05), but was similar at the conclusion of exercise, and no significant differences in heart rate or perceived exertion were observed.

CONCLUSIONS:

Three day altered sodium intake influenced urinary sodium excretion and sweat [Na+], and the rise in rectal temperature, but had no effect on perceived exertion during moderate-intensity exercise in hot ambient conditions.

KEYWORDS:

Cycling; Endurance; Plasma osmolality; Plasma volume; Running; Salt; Sweat

PMID:
31377851
DOI:
10.1007/s00421-019-04199-2

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