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Oral L-Tyrosine Supplementation Improves Core Temperature Maintenance in Older Adults.

  • 2019-10-11
  • Medicine and science in sports and exercise 52(4)
    • James A Lang
    • Alex C Krajek
    • Kelsey S Schwartz
    • Joel E Rand

Study Design

Type
Randomized Controlled Trial (RCT)
Population
nine young (25 ± 3 yr) and nine older (72 ± 8 yr) participants
Methods
randomized, double-blind design, participants ingested either 150 mg·kg of L-tyrosine or placebo before 90 min of whole-body cooling
Blinding
Double-blind
Duration
90 min

Introduction

During cold exposure, an increase in sympathetic nerve activity evokes vasoconstriction (VC) of cutaneous vessels to minimize heat loss. In older adults, this reflex VC response is impaired thereby increasing their susceptibility to excess heat loss and hypothermia. Because L-tyrosine, the amino acid substrate necessary for catecholamine production, has been shown to augment reflex VC in age skin, we hypothesize that oral ingestion of L-tyrosine will attenuate the decline in core temperature (Tc) during whole-body cooling in older adults.

Methods

In a randomized, double-blind design, nine young (25 ± 3 yr) and nine older (72 ± 8 yr) participants ingested either 150 mg·kg of L-tyrosine or placebo before commencing 90 min of whole-body cooling to decrease skin temperature to approximately 29.5°C. Esophageal temperature and forearm laser Doppler flux (LDF) were measured continuously throughout the protocol to provide an index of Tc and skin blood flow, respectively. The change in esophageal temperature (ΔTES) was the difference in temperature at the end of cooling subtracted from baseline. Cutaneous vascular conductance (CVC) was calculated as CVC = LDF/mean arterial pressure and expressed as a percent change from baseline (%ΔCVCBASELINE).

Results

Oral tyrosine ingestion augmented the cutaneous VC response to cooling in older adults (placebo, 14.4 ± 2.0; tyrosine, 32.7% ± 1.7% ΔCVCBASELINE; P < 0.05). Additionally, tyrosine improved Tc maintenance throughout cooling in older adults (placebo, -0.29 ± 0.07; tyrosine, -0.07 ± 0.07 ΔTES; P < 0.05). Both the cutaneous VC and Tc during cooling were similar between young and older adults supplemented with tyrosine (P > 0.05).

Conclusions

These results indicate that L-tyrosine supplementation improves Tc maintenance in response to acute cold exposure in an older population.

Research Insights

  • L-Tyrosine→Improved Core Temperature Regulation

    Additionally, tyrosine improved Tc maintenance throughout cooling in older adults (placebo, -0.29 ± 0.07; tyrosine, -0.07 ± 0.07 ΔTES; P < 0.05).

    Effect
    Beneficial
    Effect size
    Small
    Dose
    150 mg/kg
  • L-Tyrosine→Improved Cutaneous Vasoconstriction

    Oral tyrosine ingestion augmented the cutaneous VC response to cooling in older adults (placebo, 14.4 ± 2.0; tyrosine, 32.7% ± 1.7% ΔCVCBASELINE; P < 0.05).

    Effect
    Beneficial
    Effect size
    Moderate
    Dose
    150 mg/kg
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