From the Guidelines
Excessive vitamin C intake may increase kidney stone risk, particularly in individuals already prone to stone formation, as it can increase urinary oxalate levels, a key component of most kidney stones, as noted in studies such as 1. To minimize this risk, several strategies can be employed:
- Limit daily vitamin C intake to 90 mg for men and 75 mg for women, with an upper limit of 2,000 mg per day from all sources.
- Spread vitamin C intake throughout the day rather than taking large doses at once.
- Stay well-hydrated with 2-3 liters of water daily to help dilute the urine and reduce the concentration of stone-forming substances.
- Consume adequate dietary calcium, which can bind to oxalate in the intestines and reduce its absorption into the bloodstream, as discussed in 1.
- Obtain vitamin C primarily from fruits and vegetables rather than supplements when possible, as these sources also provide other nutrients that may help mitigate stone risk.
- Individuals with a history of calcium oxalate kidney stones should be especially cautious and may need to restrict vitamin C supplementation to lower doses or avoid it altogether, considering the guidance from 1. It's also important for people with kidney disease, recurrent stone formation, or those taking medications that affect kidney function to consult healthcare providers before taking vitamin C supplements, given the potential for increased risk as outlined in various studies including 1.
From the Research
Excess Vitamin C and Kidney Stone Formation
- The relationship between excess vitamin C intake and kidney stone formation is complex, with some studies suggesting a potential link while others find no significant association 2, 3, 4.
- A study published in 1997 found that high doses of vitamin C do not increase the risk of calcium oxalate kidney stones due to physiological regulatory factors, but recommended that recurrent stone formers and patients with renal failure restrict daily vitamin C intakes to approximately 100 mg 2.
- In contrast, a 2016 prospective cohort analysis found that total and supplemental vitamin C intake was significantly associated with a higher risk of incident kidney stones in men, but not in women 3.
- Another study published in 2003 found that vitamin C supplementation increased urinary oxalate excretion and the risk of calcium oxalate crystallization in calcium stone-forming patients 4.
- The role of diet in kidney stone formation is not fully understood, and more research is needed to determine the effects of dietary interventions on the risk of stone formation 5, 6.
- A 2007 review of the literature found that evidence-based practice guidelines for dietary changes to prevent kidney stone formation are limited, and that current patient education is largely based on intuition 6.
Key Findings
- High doses of vitamin C may not increase the risk of calcium oxalate kidney stones in healthy individuals 2.
- Vitamin C supplementation may increase urinary oxalate excretion and the risk of calcium oxalate crystallization in calcium stone-forming patients 4.
- Total and supplemental vitamin C intake is associated with a higher risk of incident kidney stones in men, but not in women 3.
- Dietary intervention is a key component in the management of uric acid nephrolithiasis, and urinary calcium and oxalate excretion should be monitored in patients with pure UA calculi to reduce the risk of mixed stone formation with calcium oxalate 5.