Effects of dietary nitrate supplementation on the response to extremity cooling and endothelial function in individuals with cold sensitivity. A double blind, placebo controlled, crossover, randomised control trial.

Double-blind, placebo-controlled, randomized crossover trial in cold-sensitive adults in the United Kingdom. Fourteen participants were randomized to start in either order; 13 completed the study (4 women, 9 men; age 34.5 ± 13.2 y).

Acute ingestion of 140 mL concentrated beetroot juice providing 11.9 mmol nitrate, taken 1.5 hours before laboratory testing. The active regimen was compared with nitrate-depleted concentrated beetroot juice placebo in a double-blind crossover design.

Acute beetroot-derived nitrate increased plasma nitrate and nitrite but did not improve cold-rewarming, endothelial function, blood pressure, or thermal perception in cold-sensitive individuals. Plasma nitrate rose from 53.1 ± 29.4 mM at baseline to 756.8 ± 175.2 mM after nitrate supplementation, and plasma nitrite rose from 73.7 ± 48.8 nM to 501.5 ± 245.8 nM, both P < 0.001. There was no effect on skin blood flow in the great toe or thumb, no effect on skin temperature during rewarming, and no difference in acetylcholine-mediated vasodilation at the forearm, finger, or foot. Resting systolic blood pressure was unchanged (121 ± 9 mmHg placebo vs 124 ± 13 mmHg nitrate), and beetroot juice was well tolerated aside from beeturia and discoloured stools.

The study was small, with only 13 completers and some outcomes analyzed in n = 11 to 13. It assessed only a single acute dose, so results do not address whether repeated or chronic nitrate supplementation could have different effects. Generalizability is limited to a subclinical cold-sensitive population under controlled laboratory conditions.