REN and Hypertension: Parati et al. (2014) found that in healthy volunteers exposed to acute exposure to an altitude of 3,400 m for 3 days, the RAS was partially inhibited. The RAS was completely suppressed at 5,400 m and plasma renin activity, Ang II concentration, and aldosterone levels were significantly reduced. Studies on patients with hypertension have also confirmed that exposure to high-altitude hypoxic conditions suppresses the RAS (Bilo et al., 2015). Moreover, long-term inhibition of the RAS can reduce vascular stiffness and alter the structure and function of blood vessels (Mitchell et al., 2007).