Effect of Dietary Nitrate Supplementation with Beet Root Juice on Thermoregulatory and Cardiovascular Responses to Extreme Heat in Aged Humans

Abstract

PURPOSE: To test the hypothesis that dietary nitrate supplementation with beet root juice attenuates cardiovascular and thermal strain in aged individuals during prolonged non-encapsulated environmental heat stress. METHODS: Study participants were eight healthy, normotensive, non-obese, aged individuals (66 ± 5 years; BMI: 24.6 kg/m2; five females). Before (PRE) and after (POST) 1 week of daily nitrate supplementation with concentrated beet root juice (140 ml twice daily), participants were exposed to 42.5°C and 35% relative humidity conditions for 2 h. Core and skin temperatures, arterial blood pressures, heart rate, cutaneous blood flow and vascular conductance, and forearm blood flow and vascular conductance were measured throughout the exposure. RESULTS: Following nitrate supplementation, mean arterial pressure decreased from 88 ± 5 to 80 ± 7 mmHg (P = 0.02) in thermoneutral conditions. During a subsequent heat stress, mean arterial pressure was significantly lower POST vs. PRE (treatment x time interaction: P < 0.01); however, this effect was limited to the first 30 min of the heat exposure. No effect of dietary nitrate supplementation was observed on core temperature, mean skin temperature, heart rate, cutaneous blood flow, cutaneous vascular conductance, forearm blood flow, and forearm vascular conductance throughout heat stress (P > 0.05). CONCLUSION: Our results indicate that in aged individuals, dietary nitrate supplementation does not attenuate thermal strain, and only transiently reduces cardiovascular strain, during extreme heat stress.