Research has been limited and mixed with regards to the effect of normal, short-term dietary sodium (Na) intake on sweat Na concentration ([Na]) and total sweat Na losses during exercise.
Purpose:
To determine the relation between dietary Na intake during exercise and up to 48-h before exercise on whole-body (WB) sweat [Na] and total sweat Na loss during 90 min of moderate-intensity cycling in the heat.
Methods:
Forty-nine recreational athletes (34 men, 15 women; 34 ± 4 years; 75 ± 12 kg) cycled for 90 min at 78 ± 5% HR_max in the heat (32⁰C, 25-50% RH). The WB washdown technique was used to collect sweat electrolytes during exercise and ion chromatography analysis was used to determine sweat [Na]. Total sweat Na loss was the product of WB sweat [Na] and WB sweat loss. Subjects were instructed to consume their normal diet before their trials. Upon arriving to the lab, each subject turned in a diet log, which included specific portion sizes and brand/type for all foods, fluids, and dietary supplements consumed in the previous 48 h. The investigators reviewed the diet logs for completeness with the subjects. Na intake was determined by Registered Dietitians using a computer based dietary analysis tool. Na intake during the trial was determined from the volume of 6% carbohydrate electrolyte (38 mmol/L Na) solution consumed ad libitum. Pearson correlation analysis was used to determine the relation between Na intake versus WB sweat [Na] and total sweat Na loss. Data are shown as mean ± SD.
Results:
WB sweat [Na] was 41.1 ± 15.6 mmol/L and total sweat Na losses were 60.9 ± 35.3 mmol. Na intake during exercise, 24-h and 48-h before exercise were 32.4 ± 18.0 mmol, 188 ± 102 mmol, and 350 ± 159 mmol. There were no significant correlations between dietary Na intake and WB sweat [Na] (r = -0.002 to 0.02, p=0.90-0.99) or total sweat Na losses (r = 0.07 to 0.19, p=0.20-0.61) for any of the comparisons.
Conclusion:
There were no correlations between normal dietary Na intake during and up to 48 h before exercise versus WB sweat [Na] or total sweat Na losses. These results suggest that short-term Na intake does not play a significant role in explaining the inter-individual differences in WB sweat Na during exercise.