Short-term cocoa bioflavanol supplementation does not improve cold-induced vasodilation in young healthy adults.

PURPOSE: Cold-induced vasodilation (CIVD) is an oscillatory rise in blood flow to glabrous skin that occurs in cold-exposed extremities. Dietary flavanols increase bioavailable nitric oxide, a proposed mediator of CIVD through active vasodilation and/or withdrawal of sympathetic vascular smooth muscle tone. However, no studies have examined the effects of flavanol intake on extremity skin perfusion during cold exposure. We tested the hypothesis that acute and 8-day flavanol supplementation would augment CIVD during single-digit cold water immersion (CWI). METHODS: Eleven healthy adults (24 ± 6 years; 10 M/1F) ingested cocoa flavanols (900 mg/day) or caffeine- and theobromine-matched placebo for 8 days in a double-blind, randomized, crossover design. On Days 1 and 8, CIVD was assessed 2 h post-treatment. Subjects immersed their 3rd finger in warm water (42 °C) for 15 min before CWI (4 °C) for 30 min, during which nail bed and finger pad skin temperature were measured. RESULTS: Flavanol ingestion had no effect on CIVD frequency (Day 1, Flavanol: 3 ± 2 vs. Placebo: 3 ± 2; Day 8, Flavanol: 3 ± 2 vs. Placebo: 3 ± 1) or amplitude (Day 1, Flavanol: 4.3 ± 1.7 vs. Placebo: 4.9 ± 2.6 °C; Day 8, Flavanol: 3.9 ± 1.9 vs. Placebo: 3.9 ± 2.0 °C) in the finger pad following acute or 8-day supplementation (P > 0.05). Furthermore, average, nadir, and apex finger pad temperatures during CWI were not different between treatments on Days 1 or 8 of supplementation (P > 0.05). Similarly, no differences in CIVD parameters were observed in the nail bed following supplementation (P > 0.05). CONCLUSION: These data suggest that cocoa flavanol ingestion does not alter finger CIVD. Clinical Trial Registration Clinicaltrials.gov Identifier: NCT04359082. April 24, 2020.

Effect of localized microclimate heating on peripheral skin temperatures and manual dexterity during cold exposure.

Reduced dexterity is a major problem in cold weather, with a need for a countermeasure that increases hand (Thand) and finger (Tfing) temperatures and improves dexterity. The purpose of this study was to determine whether electric heat (set point, 42°C) applied to the forearm (ARM, 82 W), face (FACE, 9.2 W), or combination of both (COMB, 91.2 W), either at the beginning of cold exposure (COLD; 0.5°C, 120 min; 2 clo insulation, seated, bare-handed) or after Tfing fell to 10.5°C [delayed trials (D)], improves Thand, Tfing, dexterity, and finger key pinch strength (Sfing). Volunteers ( n = 8; 26 ± 9 yr) completed 7 experimental trials in COLD: ARM, ARM-D, FACE, FACE-D, COMB, COMB-D, and no heating (CON). Temperatures were measured before (BASE) and throughout COLD. Tests of dexterity [Purdue Pegboard assembly (PP) and magazine loading (MAGLOAD)] and Sfing were measured at BASE and after 45 and 90 min of COLD. Data presented are at minute 90. Thand was warmer ( P < 0.001) during ARM (18.0 ± 2.6°C) and COMB (18.9 ± 2.0°C) versus CON (15.3 ± 1.5°C) and FACE (15.8 ± 1.5°C) for heating that was initiated at the beginning of COLD. Tfing was higher ( P < 0.04) during COMB (12.7 ± 5.1°C) versus CON (9.7 ± 2.1°C) and FACE (8.9 ± 2.2°C). The change from BASE for PP (no. of pieces) was less ( P < 0.005) in COMB (-4.5 ± 3.3) and ARM (-5.0 ± 6.0) versus CON (-13.0 ± 7.3) and FACE (-10.0 ± 8.3), and for MAGLOAD, it tended ( P = 0.06) to be less in COMB (-8.9 ± 6.2 cartridges) versus CON (-14.8 ± 3.7 cartridges). There was no change in Sfing from BASE (10.5 kg) to minute 90 in ARM or COMB (0.7 ± 1.4 and -0.2 ± 1.7 kg, respectively) but a decrease ( P < 0.01) in CON and FACE (-2.1 ± 2.0 and -1.6 ± 1.9 kg, respectively). There were no differences in Thand, Tfing, dexterity, and Sfing at minute 90 when comparing heating that was initiated at the beginning of COLD versus delayed heating. In conclusion, heating using either COMB or ARM, compared with CON and FACE, improved Thand and Tfing and reduced the decline in dexterity by 20%-50% and Sfing by 90%. Furthermore, delayed heating had no deleterious effect on Thand, Tfing, dexterity, and Sfing compared with heating that started at the beginning of cold exposure. NEW & NOTEWORTHY The present study demonstrated that, during sedentary cold air exposure, localized heating that was applied from the beginning of cold exposure on the forearm increases hand and finger temperatures and finger strength, leading to subsequent improvements in manual dexterity. In addition, localized heating that was delayed until finger temperatures cooled significantly also caused higher peripheral temperatures, leading to better strength and manual dexterity, compared with no heating.