The antioxidant vitamins C and E

vitamin C raised urinary oxalate nearly 50% (P < 0.05), urinary oxalate values
remained within the normal range (228–684 µmol/d). In six healthy subjects, vitamin
C supplementation, 10 g/d, did not alter urinary oxalate in five of the subjects, and the
elevated level noted in the remaining subject was within the normal range (30).
These data indicate that high doses of vitamin C alter urinary excretion of uric
and oxalate acid; however, diets high in purines, organ meats and fish, or chronic lowdose
aspirin, can cause hyperuricosuria, and foods rich in oxalates (e.g., tea, coffee,
nuts, beans, chocolates) can increase oxalate concentrations in urine to levels above
the normal range (31). Hence vitamin C is one of many diet constituents associated
with alterations in urinary constituents of renal stones. Furthermore, diets high in animal
protein or low in fluids, bacterial products, and heavy physical exertion have also
been implicated in renal stone disease. Because uric acid can precipitate in the absence
of hyperuricosuria, and urinary saturation with calcium oxalate is common in the general
population, factors other than urinary levels of uric acid and oxalic acid are crucial
for stone formation, including renal epithelial cell responses, acid urine, and proteins
of renal tubular origin (31).
In the Harvard Prospective Health Professional Follow-Up Study (45,251 men;
751 incident cases of kidney stones after 6 y), the relative risk of developing kidney
stones in users of vitamin C supplements (≥1500 mg vitamin C daily vs.