In a double-blind randomized study, 23 competitive triathletes competi
ng in an event consisting of a 500-meter swim, a 20-km bicycle race, a
nd a 5-km run were studied after 4-week supplementation with placebo o
r 17 mmol/d Mg orotate. The tests were carried out without a break. Bl
ood was collected before and after the test, and between the different
events for assaying energy stress and membrane metabolism. Swimming,
cycling, and running times decreased in the Mg-orotate group compared
with the controls. Serum glucose concentration increased 87% during th
e test in the control group and 118% in the Mg-orotate group, while se
rum insulin increased 39% in the controls and decreased 65% in the Mg-
orotate group. Venous O-2 partial pressure increased 126% during the t
est in the controls and increased 208% in the Mg-orotate group. Venous
CO2 partial pressure after the bicycle race decreased 66% (significan
tly) in the Mg-orotate group compared with 74% in the controls. Blood
proton concentration decreased to 90% in the Mg-orotate group (signifi
cantly) compared with 98% in the controls. Blood leukocyte count incre
ased from 5.92/nL to 11.0/nL in the controls and from 5.81/nL to 9.10/
nL in the Mg-orotate group, a significant difference. Serum cortisol w
as lower in the Mg-orotate group before and after the test compared wi
th the controls. CK catalytic concentration after the test was elevate
d 140% in the controls compared with 122% Mg-orotate group. The stress
-induced modifications of energy and hormone metabolism described in t
his study indicate altered glucose utilization after Mg-orotate supple
mentation and a reduced stress response without affecting competitive
potential.