Effect of ascorbic acid consumption on urinary stone risk factors

Area of Science:

• Nephrology
• Urology
• Nutritional Science

Background:

• Ascorbic acid (AA) is suspected to increase calcium oxalate (CaOx) stone risk due to oxalate conversion and potential acidifying effects.
• Understanding the impact of AA on urinary risk factors is crucial for managing CaOx stone formation.

Purpose of the Study:

• To investigate the effect of AA consumption on urinary calcium oxalate saturation and urinary pH.
• To compare the response to AA in normal subjects versus CaOx stone formers.

Main Methods:

• A controlled metabolic study involving 12 normal subjects and 12 CaOx stone formers.
• Two 6-day study phases, each with 2 gm of AA or placebo daily.
• Analysis of 24-hour urine collections and serum chemistry on the final 2 days of each phase.

Main Results:

• No significant change in urinary pH was observed with AA consumption in either group.
• Urinary oxalate levels significantly increased in both normal subjects (20%) and stone formers (33%) during the AA phase.
• The relative saturation ratio of CaOx was significantly elevated in the AA phase for both groups.

Conclusions:

• Daily intake of 2 gm of ascorbic acid increases urinary oxalate and CaOx saturation but does not alter urinary pH.
• CaOx stone formers exhibit a similar response to AA as normal subjects.
• Limiting daily AA intake to less than 2 gm is recommended for individuals with a history of CaOx stones.