Applied nutritional investigationThe safety of oral use of l-glutamine in middle-aged and elderly individuals

ObjectiveTo evaluate the safety of nutraceutical oral administration of l-glutamine (l-Gln) in middle-aged and elderly individuals.MethodsIn this randomized, crossover, double-blind clinical study, 30 residents of a long-term-care institution, selected according to a modified SENIEUR protocol (Working Party of the EURAGE Concerted Action Programme on Ageing of the European Community), were studied. Fourteen subjects received orally 0.5 g · kg−1 · d−1 of l-Gln and 16 received calcium caseinate for 14 d, followed by a 5-d washout. Supplements were switched for the second 14-d trial. Laboratory tests for hepatic and renal functions and ammonemia were performed and the estimated glomerular filtration rate (eGFR) was calculated.ResultsOf the 30 subjects, 16 were men, mean age was 69 ± 8.8 y, average weight was 61.8 ± 14.2 kg, and mean serum albumin was 4.0 ± 0.3 g/dL. Neither adverse clinical effects nor clinically significant laboratory changes were noted during l-Gln supplementation. There was no difference in ammonemia between the groups. There were statistically but not clinically significant increases in plasma urea nitrogen and creatinine concentrations. There was no significant decrease in eGFR during calcium caseinate supplementation (−2.9%). The eGFR decreased significantly after l-Gln supplementation (−13.3%) but well below the 25% limit for biologic significance.ConclusionIncreases in serum urea nitrogen and creatinine and decrease in eGFR are probably due to difficulties by older kidneys in metabolizing the supplemented protein sources. Although not clinically significant, those alterations impose a rigorous control on the evaluation parameters of renal function during oral l-Gln supplementation, with doses of 0.5 g · kg−1 · d−1 in middle-aged and elderly individuals.