Obad A, Valic Z, Palada I, Brubakk AO, Modun D, Dujic Z. Antioxidant pretreatment and reduced arterial endothelial dysfunction after diving. Aviat Space Environ Med 2007; 78:1114–20. Introduction: We have recently shown that a single air dive leads to acute arterial vasodilation and impairment of endothelium-dependent vasodilatation in humans. Additionally we have found that predive antioxidants at the upper recommended daily allowance partially prevented some of the negative effects of the dive. In this study we prospectively evaluated the effect of long-term antioxidants at a lower RDA dose on arterial endothelial function. Methods: Eight professional male divers performed an open sea air dive to 30 msw. Brachial artery flow-mediated dilation (FMD) was assessed before and after diving. Results: The first dive, without antioxidants, caused significant brachial arterial diameter increase from 3.85 ± 0.55 to 4.04 ± 0.5 mm and a significant reduction of FMD from 7.6 ± 2.7 to 2.8 ± 2.1%. The second dive, with antioxidants, showed unchanged arterial diameter and significant reduction of FMD from 8.11 ± 2.4 to 6.8 ± 1.4%. The FMD reduction was significantly less with antioxidants. Vascular smooth muscle function, assessed by nitroglycerine (endothelium-independent dilation), was unaffected by diving. Discussion: This study shows that long-term antioxidant treatment at a lower RDA dose ending 3–4 h before a dive reduces the endothelial dysfunction in divers. Since the scuba dive was of a similar depth and duration to those practiced by numerous recreational divers, this study raises the possibility of routine predive supplementation with antioxidants.