Elevated blood pressure follows physiological body-water conservation

Abstract

Background: Pre-clinical evidence suggests that blood pressure (BP) increase is part of an adaptive physiological body response designed to prevent under-hydration. This idea challenges established thinking that hypertension is caused by initial salt-driven over-hydration. We tested the hypothesis that this alternative view also holds true in humans. Methods: In a mechanistic study, we investigated the interrelation between daily Na+ and water intake, renal solute and water excretion, renal water conservation, and body Na+ balance with BP in 6 healthy men living in a controlled environment for 205 days. In an additional daily-life observational study we investigated the interrelation between BP and adaptive-physiological water and Na+ conservation in 108 Singaporeans. Results: In participants living under controlled conditions, BP increased when urine osmolality was high, and fluid intake or urine volume was low. This BP-increasing water conservation response was not caused by body Na+ retention. Similarly, participants living under daily-life conditions showed a BP-elevating adaptive body water conservation response with increased plasma solute concentration, increased plasma vasopressin levels, and reduced urine volume production due to reduced renal free-water excretion. Participants with higher BP relied on more urea and glucose solutes, but on less Na+ solutes, to maintain their hydration status. Participants with essential hypertension showed more pronounced adaptive-physiological water conservation. None of these hypertension-specific water conservation responses were accompanied by differences in 24-h Na+ excretion. Conclusions: BP increase in humans is part of a systemic body water conservation response that occurs largely independent of body Na+ balance. The Mars500 Salt and Water Homeostasis Project was realized by grant support from the German Federal Ministry for Economics and Technology/DLR Forschung unter Weltraumbedingungen (50WB1624-50WB2024) and the Interdisciplinary Centre for Clinical Research (IZKF Junior Research Group 2), Friedrich-Alexander-University of Erlangen-Nuremberg to JT. The food products were donated by APETITO, Coppenrath und Wiese, ENERVIT, HIPP, Katadyn, Kellogg, Molda, and Unilever. The Sodium Storage in Singaporeans Project was realized with grant support from Duke NUS Medical School (Duke-NUS-KBrFA/2019/0026) to JT. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.