Explaining variation in sweat sodium concentration: effect of individual characteristics and exercise, environmental, and dietary factors

• Published in: Journal of applied physiology (1985) 2022-12, Vol.133 (6), p.1250-1259
• Main Authors: Baker, Lindsay B, De Chavez, Peter John D, Nuccio, Ryan P, Brown, Shyretha D, King, Michelle A, Sopeña, Bridget C, Barnes, Kelly A
• Format: Article
• Language: English
• Subjects: Acclimatization; Age factors; Air temperature; Body mass; Cycles; Diet; Dietary intake; Energy expenditure; Heat acclimatization; Hot Temperature; Humans; Independent variables; Male; Males; Minority & ethnic groups; Physical training; Relative humidity; Retrospective Studies; Seasons; Sex; Sodium; Sodium, Dietary; Specific gravity; Sweat; Sweating
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00391.2022

This study determined the relative importance of several individual characteristics and dietary, environmental, and exercise factors in determining sweat [Na ] during exercise. Data from 1944 sweat tests were compiled for a retrospective analysis. Stepwise multiple regression ( < 0.05 threshold for inclusion) and values were used to express the relative importance of each factor in a model. Three separate models were developed based on available independent variables: (1,944 sweat tests from 1,304 subjects); (subset with energy expenditure: 1,003 sweat tests from 607 subjects); (subset with energy expenditure, dietary sodium, and V̇o : = 48). Whole body sweat [Na ] was predicted from forearm sweat patches in and directly measured using whole body washdown in . There were no significant effects of age group, race/ethnicity, relative humidity, exercise duration, pre-exercise urine specific gravity, exercise fluid balance, or dietary or exercise sodium intake on any model. Significant predictors in (adjusted = 0.17, < 0.001) were season of the year (warm, = -6.8), exercise mode (cycling, = 6.8), sex (male, = 4.9), whole body sweating rate ( = 4.5), and body mass ( = -3.0). Significant predictors in (adjusted = 0.19, < 0.001) were season of the year (warm, = -5.2), energy expenditure ( = 4.7), exercise mode (cycling, = 3.6), air temperature ( = 3.0), and sex (male, = 2.7). The only significant predictor in ( = 0.23, < 0.001) was energy expenditure ( = 3.8). In summary, the models accounted for 17%-23% of the variation in whole body sweat [Na ] and energy expenditure and season of the year (proxy for heat acclimatization) were the most important factors. This comprehensive analysis of a large, diverse data set contributes to our overall understanding of the factors that influence whole body sweat [Na ]. The main finding was that energy expenditure was directly associated with whole body sweat [Na ], potentially via the relation between energy expenditure and whole body sweating rate (WBSR). Warmer months (proxy for heat acclimatization) were associated with lower whole body sweat [Na ]. Exercise mode, air temperature, and sex may also have small effects, but other variables (age group, race/ethnicity, fluid balance, sodium intake, relative V̇o ) had no association with whole body sweat [Na ]. Taken together, the models explained 17%-23% of the variation in whole body sweat [Na ].