Folic acid supplementation does not attenuate thermoregulatory or cardiovascular strain of older adults exposed to extreme heat and humidity

Folic acid supplementation reverses age-related reductions in cutaneous vasodilation during passive heating. However, it is unknown if folic acid supplementation alleviates thermoregulatory and cardiovascular strain experienced by older adults during heat exposure. We evaluated the effect of folic acid supplementation on thermoregulatory and cardiovascular responses of 9 healthy older adults (61–72 yrs, 3 males/6 females) exposed to extreme heat and humidity. Participants rested at 42°C while relative humidity was increased from 30% to 70% in 2% increments every 5 minutes. The protocol was performed before (CON) and after (FOLIC) 6 weeks of folic acid supplementation (5 mg/day). Local cutaneous vascular conductance (CVC, laser-Doppler flowmetry), forearm vascular conductance (FVC, Doppler ultrasound), mean skin and esophageal temperatures, heart rate, blood pressure and cardiac output were measured. Folic acid supplementation increased fasting serum folate concentrations (P<0.01). Absolute CVC was greater throughout the protocol following supplementation (CON: 1.29 ± 0.16 units/mmHg vs. FOLIC: 1.65 ± 0.24 units/mmHg, P<0.01). However, normalized CVC (CON: 54 ± 8% vs. FOLIC: 59 ± 7%, P=0.22), FVC (CON: 3.47 ± 0.76 ml/mmHg vs. FOLIC: 3.40 ± 0.56 ml/mmHg, P=0.93), mean skin (P=0.81) and esophageal (CON: 36.87 ± 0.28°C vs. FOLIC: 36.90 ± 0.25°C, P=0.98) temperatures, heart rate (CON: 83 ± 10 beats/min vs. FOLIC: 84 ± 8 beats/min, P=0.64), blood pressure (P=0.71), and cardiac output (P=0.20) were unaffected by folic acid supplementation. These results demonstrate that 6 weeks of folic acid supplementation does not alleviate thermoregulatory or cardiovascular strain of healthy older adults exposed to extreme heat and humidity.