Oral l-Tyrosine Supplementation Improves Core Temperature Maintenance in Older Adults

Abstract

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 (T c) 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−1 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 T c and skin blood flow, respectively. The change in esophageal temperature (ΔT ES) 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 T c maintenance throughout cooling in older adults (placebo, −0.29 ± 0.07; tyrosine, −0.07 ± 0.07 ΔT ES; P < 0.05). Both the cutaneous VC and T c during cooling were similar between young and older adults supplemented with tyrosine (P > 0.05). Conclusions These results indicate that l-tyrosine supplementation improves T c maintenance in response to acute cold exposure in an older population.

Effect of aging on cardiovascular responses to cold stress in humans

“…Consequently, the ability of cutaneous microvascular constriction is diminished in the elderly by increased oxidative stress [48][49] . Therefore, direct injection of BH4 [50] or tyrosine [51] or oral ingestion of a pharmacological source of BH4, sapropterin [52] or L-tyrosine [53][54] improved core temperature maintenance and augments the cutaneous reflex vasoconstriction response to cooling in older adults. Collectively, these studies demonstrate that reduced noradrenergic neurotransmitter biosynthesis may blunt reflex cutaneous vascular response to cold stress in older adults.…”

“…This autoregulation driven by the sympathetic system causes vasodilation of coronary arteries to ensure constant coronary blood flow [41,[52][53][54][55] . The physically and functionally normal coronary arteries dilate in response to cold exposure [55] .…”

Synthesis of l-Tyrosine by Pichia pastoris Displaying Tyrosine Phenol Lyase

“…In the food industry, it is extensively used as a dietary supplement. For instance, it can be used as a nutritional supplement for patients with phenylketonuria, , a dietary supplement for patients with nemaline myopathy to improve strength and exercise tolerance, and an oral supplement to improve the vasoconstriction response of the elderly during whole-body cooling and to improve core temperature maintenance for the elderly who are facing acute cold exposure. , In addition, l -tyrosine decreases diastolic blood pressure and improves cognitive function under stress and attenuates mood disorders under low temperatures and hypoxic stress . In the medical field, l -tyrosine is used as a precursor for the synthesis of L-DOPA, which can be used as an essential anti-Parkinson’s medicine .…”

The effect of taurine supplementation on physiological and thermoregulatory responses in humans during rest and exercise in hot environmental conditions

“…However, tyrosine is an essential substrate for tyrosine hydroxylase, which is involved in axonal catecholamine synthesis (particularly norepinephrine; Fernstrom & Fernstrom, 2007). Thus, sufficient tyrosine availability is required to maintain catecholamine levels and facilitate sympathetic vasoconstrictive effects on the subcutaneous vasculature (Lang et al, 2020). This has been reported to attenuate the rate of cold-induced decline in Tcore among those likely to have tyrosine deficiency (Lang et al, 2020), but there were no similar effects reported across studies conducted in the heat.…”

“…Furthermore, among those with potential acute or chronic tyrosine deficiency, dietary supplementation may offer greater availability to maintain catecholamine levels, which are important for sympathetic vasoconstrictive effects on the subcutaneous vasculature (Lang et al, 2020) and may impact upon both dry and evaporative thermoregulatory defences. Given that both tyrosine and BCAAs may compete for the same blood-brain-barrier transporters, coupled with their wider roles in neurotransmitter biosynthesis pathways (Fernstrom, 1981;Pardridge, 1998;Suryawan et al, 1998), sufficient balance of both supplements may be important during heat exposure.…”