Disclosed herein is the use of a composition containing a natural antioxidant quercetin, vitamin C, and vitamin B3 in the manufacture of a medicament for increasing glomerular filtration rate in a subject for improving renal function, wherein the composition has a weight ratio of 1 : 0.2-2.5 : 0.02-1 between quercetin, vitamin C, and vitamin B3, and wherein the composition may further contain folic acid.