Dietary tyrosine benefits cognitive and psychomotor performance during body cooling

Supplemental tyrosine is effective at limiting cold-induced decreases in working memory, presumably by augmenting brain catecholamine levels, since tyrosine is a precursor for catecholamine synthesis. The effectiveness of tyrosine for preventing cold-induced decreases in physical performance has not been examined. This study evaluated the effect of tyrosine supplementation on cognitive, psychomotor, and physical performance following a cold water immersion protocol that lowered body core temperature. Fifteen subjects completed a control trial (CON) in warm (35 °C) water and two cold water trials, each spaced a week apart. Subjects ingested an energy bar during each trial; on one cold trial (TYR) the bar contained tyrosine (300 mg/kg body weight), and on the other cold trial (PLB) and on CON the bar contained no tyrosine. Following each water immersion, subjects completed a battery of performance tasks in a cold air (10 °C) chamber. Core temperature was lower (p = 0.0001) on PLB and TYR (both 35.5 ± 0.6 °C) than CON (37.1 ± 0.3 °C). On PLB, performance on a Match-to-Sample task decreased 18% (p = 0.02) and marksmanship performance decreased 14% (p = 0.002), compared to CON, but there was no difference between TYR and CON. Step test performance decreased by 11% (p = 0.0001) on both cold trials, compared to CON. These data support previous findings that dietary tyrosine supplementation is effective for mitigating cold-induced cognitive performance such as working memory, even with reduced core temperature, and extends those findings to include the psychomotor task of marksmanship.