Sauna therapy has been shown to have benefits to cardiovascular health. Changes in hematocrit, hemoglobin, and plasma volume in response to sauna heating are not well defined in the middle-aged population. This population is of significant interest because of an increased rate of decline in cardiovascular health starting at middle age. PURPOSE: The purpose of this study was to examine the effect of acute sauna exposure on blood composition, specifically the change in plasma volume in young and middle-aged adults. METHODS: 10 young (24.9 ± 4.2 years, 6 male and 4 female) and 8 middle-aged adults (55.6 ± 3.9 years 4 males and 4 females) underwent 40 mins of sauna exposure (20 mins x2, 10 min recovery at 23 °C in between) at 80°C followed by a 90 min rest period. Blood samples were taken before sauna exposure (PRE) and after the 90-minute recovery period (POST). Hemoglobin and hematocrit levels were measured, and total plasma volume was calculated using the Dill and Costill equation. Semi-nude body mass was recorded at baseline and after the 90 min recovery period. RESULTS: Hemoglobin concentration increased and body mass decreased following sauna exposure (P= 0.046, P<0.001, respectively) with no significant effect of age (P=0.157, P=0.449, respectively). There was no significant change in plasma volume PRE vs POST sauna (P=0.459) or hematocrit (P=0.097). Additionally, there was no effect of age on plasma volume in both the young and old populations (young recovery plasma volume = 99.11 ± 1.5% of baseline, old recovery plasma volume = 100 ± 2.8% of baseline) (P=0.368). CONCLUSION: An acute sauna exposure (40 min, 80°C) results in increased hemoglobin concentration and an acute reduction in body mass in individuals ages 18-60. The reduction in body mass during acute sauna exposure, however, does not result in a change in plasma volume in both young and middle-aged individuals.



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