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Exercise-induced hypohydration may impair endothelial function
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Mild hypohydration brought on by exercise and fluid restriction can cause endothelial dysfunction, researchers reported in the European Journal of Nutrition.
“You could be mildly dehydrated without knowing it while you have endothelial impairment similar to smoking a cigarette,” Stavros Kavouras, PhD, FACSM, FECSS, associate professor and coordinator of the exercise science program at the University of Arkansas, said in a press release. “The degree of dehydration when these changes occur is at less than 2% dehydration, which is around the threshold when people start feeling thirsty.”
Stavros Kavouras
For a recent study, 10 active, healthy young men (average age, 24 years) were required to follow a standardized diet (55% carbohydrates, 30% fat and 15% protein) the day before and during experimental testing and to avoid alcohol, caffeine and intense physical activity at least 24 hours before testing began. After an overnight 10-hour fast, baseline measurements were taken, including urine specific gravity measurement, euhydrated body weight, a blood sample and flow-mediated dilation. Then, the men engaged in brisk treadmill walking for 100 minutes, never exceeding 70% of their maximum heart rate. The participants were not provided any hydration during the exercise.
After exercise, the men were weighed again to ensure that they achieved 2% weight loss, and then for the rest of the day, they were restricted to one 500-mL bottle of mineral water. The following morning, after another 10-hour fast, the men returned to have their hydration level and endothelial function assessed again.
According to the results, the men experienced a loss of body mass of 1.9 0.1%, a decrease in plasma volume by –3.5 1.8% and an increase in serum osmolality of 9 2 mmol kg-1.
Impairment of the endothelial function was evident by the reduction in flow-mediated dilation (–26.8 3.9%; P = .018). Hypohydration also reduced the absolute change in diameter of the brachial artery after reactive hyperemia (euhydrated: 0.34 mm 0.15 mm; hypohydrated: 0.24 mm 0.1 mm; P = .009). BP and heart rate, however, did not appear to be affected.
“Even though in these young and healthy subjects heart rate, [BP] and resting diameter of the brachial artery remained unaffected, the endothelial cell layer was affected, especially after the shear stress induced by the 5-min occlusion,” the researchers wrote.
Kavouras and colleagues will next focus on the impact exercised-induced hypohydration has on men and women with diabetes and CVD. – by Tracey Romero
Disclosure: Kavouras reports active grants with Danone Research.
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