Hypohydration has been suggested as a predisposing factor for several pathologies including cardiovascular diseases (CVD). While CVD are the leading cause of death worldwide, no study has investigated whether acute hypohydration affects endothelial function and cardiovascular function.

Ten young, healthy males participated in this crossover study (age: 24.3 ± 2.3 year; weight: 80.8 ± 5.3 kg; BMI: 24.3 ± 0.4 kg m⁻²). Each subject completed two measurements of endothelial function by flow-mediated dilation (FMD) in euhydrated and hypohydrated state separated by 24 h. Following baseline assessment of hydration status and FMD, the subjects completed 100 min of low-intensity intermittent walking exercise to achieve hypohydration of −2 % of individual body mass. For the rest of the day, a standardized, low water content diet was provided. The following morning, hydration markers and endothelial function were recorded.

Hypohydration by −1.9 ± 0.1 % of body mass resulted in decreased plasma volume by −3.5 ± 1.8 % and increased plasma osmolality by 9 ± 2 mmol kg⁻¹ (P < 0.001). FMD as a response to hypohydration decreased by −26.8 ± 3.9 % (P < 0.05).

The data suggested that a small degree of hypohydration induced by moderate exercise and fluid restriction significantly impaired endothelial function.