Oral Amino Acids in Elderly Subjects: Effect on Myocardial Function and Walking Capacity

Abstract

Background: With advancing age the risk of developing serious nutritional deficiencies increases, and disturbances to the actions of insulin and insulin-like growth factor, coupled with reduced protein/amino acid (AA) intake, impair protein synthesis in muscles. Objective: To assess the effects of administering oral AAs on walking capacity and perceived walking impairment, isometric muscular strength, and myocardial function at rest and during isometric exercise. Methods: One hundred elderly subjects (aged >65 years) with reduced physical activity were randomized to receive an oral AA mixture (12 g/day) or placebo for 3 months. At baseline and after 3 months of therapy we assessed physical capacity with the 6-min walk test, and perceived physical impairment with the walking impairment questionnaire (WIQ); we assessed maximal isometric muscular strength of the right hand with a handgrip dynamometer, and left ventricular ejection fraction (LVEF) using quantitative two-dimensional echocardiography at rest and during acute overload. Results: Three months of AA treatment resulted in significant increases in 6-min walk distance (268.8 ± 34.9 vs. 212 ± 40 m, p < 0.001), WIQ scores (distance: 68.3 ± 12 vs. 53 ± 14.8%, p < 0.001; speed: 72.2 ± 14.4 vs. 52.8 ± 12%, p < 0.001; stairs: 98.2 ± 24 vs. 72.4 ± 22%, p < 0.001), and in maximal muscular isometric strength (20.2 ± 2 vs. 14 ± 2.8 kg, p < 0.001). Moreover, peak stress LVEF was higher during AA administration when compared to placebo administration (67 ± 7 vs. 56 ± 9%, p < 0.01). Left ventricular response to exercise normalized during AA administration in 24 out of 32 (75%) patients with abnormal LV response at baseline, whereas it remained unchanged in the placebo group. Conclusion: An oral AA supply such as that used in this study improves ambulatory capacity, maximal isometric muscle strength and myocardial ability to match an acute overload in elderly subjects without affecting the main metabolic parameters. These functional gains may translate into increased perceived walking capacity.