Vitamin C is an over-the-counter supplement that is used by many people due to its benefits relating to immune function and antioxidant properties. The recommended dietary allowance for vitamin C is 75-90 mg daily for adults, with 75 mg recommended for women and 90 mg recommended for men.

Many fruits and vegetables such as oranges, lemons, green peppers and broccoli are a huge source of vitamin C and are more than enough to meet daily requirements. 

Even so, vitamin C supplements are commonly used by people at large doses of 500-2000 mg per day and this trend is becoming more common nowadays after the COVID-19 pandemic.

Vitamin C in the body is broken down into oxalate, which passes through the kidneys to be eliminated in urine. Studies have shown an increase in the urinary oxalate excretion when vitamin C supplements were given to both stone patients and healthy volunteers. 

Oxalate in urine can bind to calcium, forming calcium oxalate crystals, which precipitates out of urine if found in large amounts and can form kidney stones. This can occur when there is excess oxalate in the urine as a result of vitamin C supplementation, in some cases. In fact, the risk of stone development was found to be higher among those taking vitamin C supplements.  

Contrary to supplements, natural sources of vitamin C, such as citrus fruits, contain citrate, which is actually protective against urinary stones and reduces the formation of calcium oxalate crystals. Therefore, in healthy individuals and in patients with kidney stone disease, relying on natural sources for vitamin C, instead of vitamin C-containing supplements, can easily provide the required daily intake minimizing the potential risk of urinary stone formation or recurrence.