Effects of acute dietary nitrate supplementation on cold-induced vasodilation in healthy males

Abstract

Purpose: Cold-induced vasodilation (CIVD) is a paradoxical rise in blood flow to the digits that occur during prolonged cold exposure. CIVD is thought to occur through active vasodilation and/or sympathetic withdrawal, where nitric oxide (NO) may play a key role in mediating these mechanisms. Beetroot juice (BRJ) is high in dietary nitrate (NO₃^-) which undergoes sequential reduction to nitrite (NO₂^-) and subsequently NO. Using a double-blind, randomized, crossover design, we examined the effect of acute BRJ supplementation on the CIVD response in 10 healthy males.

Methods: Participants had a resting blood pressure measurement taken prior to ingesting 140 mL of nitrate-rich BRJ (13 mmol NO₃^-) or a NO₃^--free placebo (PLA). After 2 h, participants immersed their hand in neutral water (~ 35 °C) for 10 min of baseline before cold water immersion (~ 8 °C) for 30 min. Laser-Doppler fluxmetry and skin temperature were measured continuously on the digits.

Results: Compared to PLA (100 ± 3 mmHg), acute BRJ supplementation significantly reduced mean arterial pressure at -30 min (96 ± 2 mmHg; p = 0.007) and 0 min (94 ± 2 mmHg; p = 0.008). Acute BRJ supplementation had no effect on Laser-Doppler fluxmetry during CIVD (expressed as cutaneous vascular conductance) measured as area under the curve (BRJ: 843 ± 148 PU mmHg^-1 s; PLA: 1086 ± 333 PU mmHg^-1 s), amplitude (BRJ: 0.60 ± 0.12 PU mmHg^-1; PLA: 0.69 ± 0.14 PU mmHg^-1), and duration (BRJ: 895 ± 60 s; PLA: 894 ± 46 s).

Conclusion: Acute BRJ supplementation does not augment the CIVD response in healthy males.

Keywords: Beetroot juice; CIVD; Cold; Cutaneous circulation; Finger; Skin blood flow.