Ascorbic acid does not affect the age-associated reduction in maximal cardiac output and oxygen consumption in healthy adults

Abstract

Maximal aerobic capacity (V̇o2max) decreases progressively with age, primarily because of a reduction in maximal cardiac output (Q̇max). This age-associated decline in V̇o2max may be partially mediated by the development of oxidative stress that can suppress β-adrenergic-receptor responsiveness and, consequently, reduce Q̇max. To test this hypothesis, V̇o2max (indirect calorimetry) and Q̇max (open-circuit acetylene breathing) were determined in 12 young (23 ± 1 yr, mean ± SE) and 10 older (61 ± 1 yr) adults following systemic infusion of either saline (control) and/or the powerful antioxidant ascorbic acid (acute: bolus 0.06; drip 0.02 g/kg fat-free mass) and following chronic 30-day oral administration of ascorbic acid (500 mg/day). Plasma ascorbic acid concentration was not different between young and older adults and was increased similarly, independent of age [change (Δ) acute = 1,055 ± 117%; Δ chronic = 62 ± 19%]. Oxidized low-density lipoprotein concentration was greater ( P < 0.001) in older (57 ± 5 U/l) compared with young (34 ± 3 U/l) adults and was reduced in both groups ( P < 0.02) following acute (Δ = −6 ± 2%) but not chronic ( P = 0.18) ascorbic acid administration. Control (baseline) V̇o2max and Q̇max were positively related ( r = 0.76, P < 0.001) and were lower ( P < 0.05) in older (34 ± 2 ml·kg−1·min−1; 16.1 ± 1.1 l/min) compared with young (43 ± 3 ml·kg−1·min−1; 20.2 ± 0.9 l/min) adults. Following ascorbic acid administration, neither V̇o2max (young acute = 41 ± 2; young chronic = 42 ± 2; older acute = 34 ± 2; older chronic = 34 ± 2 ml·kg−1·min−1) nor Q̇max (young acute = 20.1 ± 0.9; young chronic = 19.1 ± 0.8; older acute = 16.2 ± 1.1; older chronic = 16.6 ± 1.4 l/min) was changed. These data suggest that ascorbic acid administration does not affect the age-associated reduction in Q̇max and V̇o2max.