Ice slurry ingestion reduces human brain temperature measured using non-invasive magnetic resonance spectroscopy

Sumire Onitsuka,Daisuke Nakamura,Hideyuki Takahashi,Takuma Arimitsu,Takahiro Onishi,Hiroshi Hasegawa

doi:10.1038/s41598-018-21086-6

Abstract

We previously reported that ice slurry ingestion reduced forehead skin temperature, thereby potentially reducing brain temperature (Tbrain). Therefore, in the current study, we investigated the effect of ice slurry ingestion on Tbrain using proton magnetic resonance spectroscopy, which is a robust, non-invasive method. Eight male participants ingested 7.5 g/kg of either a thermoneutral drink (37 °C; CON) or ice slurry (−1 °C; ICE) for about 5 min following a 15-min baseline period. Then, participants remained at rest for 30 min. As physiological indices, Tbrain, rectal temperature (Tre), mean skin temperature, nude body mass, and urine specific gravity were measured. Subjective thermal sensation (TS) and thermal comfort (TC) were measured before and after the experiment. Tbrain and Tre significantly reduced after ingestion of ICE compared with after ingestion of CON, and there was a significant correlation between Tbrain and Tre. The other physiological indices were not significantly different between beverage conditions. TS and TC were significantly lower with ICE than with CON (p < 0.05). These results indicate that ice slurry ingestion can cool the brain, as well as the body’s core.

Highlights

Ice slurry ingestion, which comprises an icy mixture that is consumed like a beverage[1], has been recently reported to improve endurance exercise capacity in the heat
Another possible factor for the ergogenic effect of ice slurry ingestion in preventing central fatigue is a reduction in brain temperature (Tbrain)
We previously investigated the effects of ice slurry ingestion on forehead skin temperature in the heat, and found a significant reduction in temperature, suggesting a potential reduction in Tbrain through conductive cooling of the facial skin and brain with ice slurry ingestion[11]

Summary

Introduction

Ice slurry ingestion, which comprises an icy mixture that is consumed like a beverage[1], has been recently reported to improve endurance exercise capacity in the heat. Two mechanisms are proposed as contributing to this effect: (1) increased heat storage capacity through a reduction in core temperature and (2) a sensory effect, such as a reduction in ratings of perceived exertion or an improvement in thermal comfort (i.e., impairment of central fatigue) Another possible factor for the ergogenic effect of ice slurry ingestion in preventing central fatigue is a reduction in brain temperature (Tbrain). Siegel et al.[10] suggested that oral ingestion of ice slurries possibly resulted in conductive cooling of the facial skin and brain To verify this hypothesis, we previously investigated the effects of ice slurry ingestion on forehead skin temperature in the heat, and found a significant (vs 37 °C, p < 0.01; vs 4 °C, p < 0.001) reduction in temperature, suggesting a potential reduction in Tbrain through conductive cooling of the facial skin and brain with ice slurry ingestion[11]. Given the nature of MRS, we conducted the experiment with participants at rest in a temperate condition

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