Vitamin C is not good for kidney stones. In fact, high-dose vitamin C supplements are one of the recognized risk factors for the most common type of kidney stone, calcium oxalate stones. Your body breaks down vitamin C into oxalate, which is filtered through your kidneys and can crystallize into stones when levels get too high. The risk is dose-dependent and, interestingly, affects men and women differently.
How Vitamin C Turns Into Oxalate
When your body uses vitamin C (ascorbic acid), part of the leftover molecule breaks down through a non-enzymatic process into oxalate. Specifically, the oxidized form of vitamin C becomes an unstable compound that rapidly splits into oxalate and a harmless sugar. This isn’t a rare side effect or a malfunction. It’s a normal part of how your body processes vitamin C.
Oxalate itself isn’t dangerous in small amounts. Your kidneys filter it out in urine every day. But when oxalate levels in the urine rise too high, it binds with calcium and forms crystals. Those crystals can grow into calcium oxalate kidney stones, which account for roughly 80% of all kidney stones. The more vitamin C you take in, the more oxalate your kidneys have to deal with.
The Risk Is Real for Men
A large prospective study published in JAMA Internal Medicine found that men who took vitamin C supplements had roughly double the risk of developing kidney stones compared to men who didn’t supplement. That’s a striking increase for something many people take casually.
A separate analysis looking at total daily vitamin C intake (from food and supplements combined) found that the risk for men started climbing meaningfully at around 700 to 800 milligrams per day. Men consuming 1,000 mg or more daily had a 43% higher risk of stones compared to men consuming less than 90 mg per day. Even at the 500 to 999 mg range, the risk was 29% higher. The trend was consistent: more vitamin C, more stones.
For context, a single vitamin C supplement tablet typically contains 500 or 1,000 mg. So even one daily tablet can push you into the range where risk increases.
Women Appear Less Affected
The same pattern does not show up in women. A study in the Journal of the American Society of Nephrology followed women consuming up to 1,500 mg of vitamin C per day and found no significant increase in kidney stone risk. The research concluded that routine restriction of vitamin C to prevent stones in women “appears unwarranted.”
Larger analyses have confirmed this finding. Neither total vitamin C intake nor supplemental vitamin C intake was significantly associated with kidney stone risk in women across any dosage category tested. The reason for this sex difference isn’t fully understood, but the data is consistent across multiple studies: the link between vitamin C and stones is predominantly a male problem.
Food Sources vs. Supplements
Getting vitamin C from fruits and vegetables is far less concerning than taking supplements. The main reason is dosage. An orange contains about 70 mg of vitamin C. A cup of strawberries has around 90 mg. It’s difficult to eat enough produce to reach 700 mg per day from food alone. Supplements, on the other hand, deliver 500 to 2,000 mg in a single pill, flooding your system with far more than food ever would.
In the studies that tracked risk by intake level, the danger zone started well above what a healthy diet provides. If you eat a varied diet with plenty of fruits and vegetables, you’re getting enough vitamin C for your immune system and tissue repair without approaching risky oxalate levels. The problem is concentrated supplementation, not dietary intake.
What Urologists Recommend
The American Urological Association lists vitamin C among “stone-provoking” supplements. Their medical management guidelines note that vitamin C, at dosages much higher than those obtained from food alone, contributes to increased urine oxalate. The recommendation is straightforward: vitamin C supplements should be avoided by people at risk for kidney stones.
The National Kidney Foundation echoes this, specifically advising people with calcium oxalate stones to avoid vitamin C supplements and foods heavily fortified with vitamin C.
If you’ve had a kidney stone before (especially a calcium oxalate stone), this guidance applies directly to you. If you’ve never had a stone but take high-dose vitamin C regularly, it’s worth knowing that a 24-hour urine test can measure your oxalate levels and tell you whether your current intake is pushing you toward risk. Elevated urinary oxalate is the clearest early signal that your body is producing more oxalate than your kidneys can comfortably handle.
Who Should Be Most Careful
People with existing kidney problems face the greatest danger from high-dose vitamin C. In patients with significantly reduced kidney function, the excess oxalate can’t be cleared efficiently and builds up in the blood, a condition called oxalosis. One documented case involved a patient on dialysis who developed severely elevated blood oxalate levels, more than 100 times the normal range, linked to high-dose vitamin C ingestion. While this is an extreme scenario, it illustrates how the risk scales with kidney impairment.
Men with a history of calcium oxalate stones are the next highest-risk group, given the consistent evidence of doubled stone risk with supplementation. If you fall into either category, there’s no dose of supplemental vitamin C that current evidence supports as safe for stone prevention purposes. Stick with food sources, which provide plenty of vitamin C without the oxalate spike that comes with concentrated pills.