title: Ascorbic acid does not affect the age-associated reduction in maximal cardiac output and oxygen consumption in healthy adults.
abstract: Maximal aerobic capacity (Vo(2max)) decreases progressively with age, primarily because of a reduction in maximal cardiac output (Q(max)). This age-associated decline in Vo(2max) may be partially mediated by the development of oxidative stress that can suppress beta-adrenergic-receptor responsiveness and, consequently, reduce Q(max). To test this hypothesis, Vo(2max) (indirect calorimetry) and Q(max) (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 (Delta) acute = 1,055 +/- 117%; Delta 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 (Delta = -6 +/- 2%) but not chronic (P = 0.18) ascorbic acid administration. Control (baseline) Vo(2max) and Q(max) 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 Vo(2max) (young acute = 41 +/- 2; young chronic = 42 +/- 2; older acute = 34 +/- 2; older chronic = 34 +/- 2 ml.kg(-1).min(-1)) nor Q(max) (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 Q(max) and Vo(2max).
authors.affiliation: Department of Integrative Physiology, 354UCB, Univ. of Colorado, Boulder, CO 80309-0354, USA. christopher.bell@colorado.edu
authors.forename: Christopher
authors.initials: C
authors.lastname: Bell
authors.forename: John M
authors.initials: JM
authors.lastname: Carson
authors.forename: Nathaniel W
authors.initials: NW
authors.lastname: Motte
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Seals
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000502:physiology; D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging / Q000187:drug effects / Q000502:physiology*; D000975:Antioxidants / Q000008:administration & dosage; D001205:Ascorbic Acid / Q000008:administration & dosage*; D002302:Cardiac Output / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology*; D010807:Physical Endurance / Q000187:drug effects / Q000502:physiology*
chemical_list: D000975:Antioxidants; D001205:Ascorbic Acid