Does Vitamin C Really Cause Kidney Stones? Why that fear is mostly wrong
Based on research data, doctors will help you clarify the key, often overlooked details regarding the relationship between Vitamin C and kidney stones.
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If you’ve ever tried to take better care of your health, chances are you’ve come across this scary headline somewhere:
“Vitamin C increases your risk of kidney stones!”
For many people, that one line is enough to make them stop all supplements immediately. Some even start to worry about the vitamin C in fruits and vegetables.
But when we go back to the actual science, the story is much more nuanced – and a lot less frightening.
This article will walk you through the issue from a patient’s perspective:
- Where did the “vitamin C causes kidney stones” idea come from?
- What do large human studies really show?
- Who actually needs to be careful – and who doesn’t?
- How can you supplement vitamin C more safely if you’re still worried?
By the end, you should be able to look at vitamin C with clarity rather than fear.
It all started with oxalate in the urine – but that’s not the whole story
The suspicion that vitamin C might cause kidney stones came from one simple observation:
- Some small studies found that after taking vitamin C,
- oxalate levels in urine went up.
Because many kidney stones are made of calcium oxalate, it seemed logical to say:
“More oxalate in the urine → more calcium oxalate stones → vitamin C causes kidney stones.”
However, later work showed a critical problem:
In some of those early studies, the lab method used to measure oxalate was flawed.
In other words:
- Oxalate was sometimes created in the test tube after the urine was collected,
- not necessarily in the body before the urine came out.
So, part of the “oxalate increase” was actually a measurement artifact, not true physiology.
That’s one reason why some studies reported:
- “Oxalate goes up after vitamin C”
while others found:
- “No significant change in urinary oxalate.”
Already, this weakens the claim that “vitamin C inevitably drives oxalate sky-high.”
To make things even more interesting, there’s also a theoretical argument that vitamin C could help prevent some stones, because:
- Vitamin C can bind with calcium in the urine,
- possibly reducing the chance that oxalate binds to calcium to form crystals.
In short:
Just seeing oxalate rise in a few tests is far from proof that vitamin C directly causes kidney stones in real life.
To move beyond lab measurements, researchers did the right thing:
They started large, long-term observational studies to see whether people who take vitamin C actually get more kidney stones.
Here’s what they found.
Studies that did not find higher risk
Two major prospective cohort studies followed tens of thousands of people over many years:
- One tracked more than 45,000 men for about 6 years.
- Another followed over 85,000 women for 14 years.
They compared people who took high amounts of vitamin C (for example, ≥ 1,500 mg per day) with those who took much less (for example, < 250 mg per day).
Result:
- The high-vitamin C group did not have a higher rate of kidney stones compared to the low-intake group.
Studies that found a possible increase in risk
On the other hand, two other large studies in men reported a different pattern:
- In one study of about 45,000 men over 14 years, those who took ≥ 1,000 mg of vitamin C daily had roughly a 41% higher relative risk of developing stones compared with those who took < 90 mg.
- Another study of about 48,000 men over 11 years found that those who used vitamin C supplements (at least 7 doses per week) had about double the risk of kidney stones compared with non-users.
That sounds dramatic – “double the risk!” – and it makes great headlines.
But we have to ask: double of what?
When you look at the actual numbers, the absolute increase in risk over many years was still quite small. In other words:
The number of “extra” kidney stones that appeared among vitamin C users
was small compared with the size of the group and the long time period.
So overall, the research picture is:
- Some large studies: no increased risk
- Some large studies: modestly increased risk in men with high-dose, long-term supplement use
- All with various limitations in how diet, water intake, other diseases and stone types were measured
This is very different from “vitamin C definitely causes kidney stones in everyone.”
Big human studies: the evidence is split, not one-sided
Correlation is not causation – and kidney stones have many other triggers
Most of the big studies we’ve mentioned are observational, meaning they can only tell us:
- People who do X are more or less likely to experience Y.
They cannot prove that X directly causes Y.
A simple analogy:
- Imagine you notice that people who carry umbrellas are seen more often in wet clothes.
- That doesn’t mean umbrellas cause you to get wet.
- In reality, rain is the third factor causing both.
It’s similar with vitamin C and kidney stones:
- People who choose supplements may also have other habits or conditions that influence stones:
- how much water they drink
- how much salt, animal protein, spinach, tea, or coffee they consume
- whether they are overweight or have diabetes
- whether they already have kidney disease
Kidney stones are influenced by many factors, including:
- low fluid intake
- high salt and high animal protein diets
- obesity and metabolic syndrome
- certain medications
- high-oxalate foods
- genetic and metabolic factors
So when an observational study says:
“Men who take vitamin C supplements had more kidney stones”
what it really means is:
- “In this specific group, with all their unique habits and health conditions,
vitamin C use was associated with more stones.”
It doesn’t prove that vitamin C alone is the villain, independent of everything else.
Why media headlines make the risk look much scarier than it is
Most people will never read the original scientific articles.
Instead, they see headlines like:
“Vitamin C supplements may double your risk of kidney stones!”
A few issues with this kind of coverage:
- It usually highlights one single study, often the most negative one.
- It talks about relative risk (“double!”) and ignores absolute risk (“how many extra cases, really?”).
- It rarely mentions other large studies showing no increased risk.
- It does not explain limitations like:
- relying on people trying to remember what they ate over many years
- failure to measure actual stone composition
- not fully adjusting for diet, water, other health conditions
Why? Because:
- “Vitamin C does not increase kidney stone risk” is not a catchy headline.
- “Vitamin C may double your risk!” grabs more attention and clicks.
The result is predictable:
- The public remembers the frightening part.
- The more balanced, nuanced data is forgotten.
That’s why it’s important to look at the overall body of evidence, not just one dramatic statistic.
So… if I take vitamin C, should I be worried?
Putting all the evidence together, a more realistic picture looks like this:
- For most healthy people with normal kidney function,
usual supplemental doses of vitamin C (for example, 100–1,000 mg per day) appear to be low risk. - In some large studies of men taking high-dose supplements long term,
there may be a modest increase in kidney stone risk – but the absolute increase is small. - Women, in the largest available cohort, did not show an increased risk with higher vitamin C intake.
- People with pre-existing kidney disease or a strong personal history of stones are in a special category and should be more cautious.
A fair, science-based conclusion is:
“Vitamin C supplementation may slightly increase stone risk in some men at high doses over many years,
but for the average person with normal kidneys, the risk is low, especially at moderate doses.”
This is very different from saying:
“Vitamin C causes kidney stones.”
How to use vitamin C more safely (and more smartly)
If you still feel a bit uneasy but don’t want to miss out on the benefits of vitamin C, here are sensible strategies to reduce your risk further:
1. Don’t let vitamin C “fight alone” for years
Some of the studies showing a higher stone risk involved people who, for many years:
only took vitamin C supplements,
without considering other nutrients that affect stone formation.
We now know that other nutrients play important protective roles:
Magnesium – can help dissolve calcium oxalate crystals and reduce urinary oxalate excretion.
Vitamin B6 – involved in oxalate metabolism.
Citrate (from e.g. potassium citrate or lemon/lime) – binds with calcium and helps prevent calcium oxalate crystallization.
So instead of asking, “Is vitamin C good or bad?”
It’s better to ask:
“What does my overall nutrient pattern look like, and how can I balance it?”
2. Support your kidneys with basic lifestyle habits
Regardless of supplements, some simple habits are crucial for stone prevention:
Drink enough water so your urine stays pale and clear most of the time.
Avoid chronically high salt and excessive animal protein intake.
Be cautious with very high intakes of high-oxalate foods if you have a history of calcium oxalate stones.
Maintain a healthy weight and manage metabolic conditions such as diabetes or metabolic syndrome.
These factors probably have more impact on stone risk than vitamin C alone.
3. Know if you belong to a higher-risk group
Talk to your doctor before taking high-dose vitamin C if you:
have known chronic kidney disease
have a history of recurrent kidney stones
have only one kidney or structural kidney abnormalities
are already on multiple medications affecting kidneys or electrolytes
In these situations, vitamin C may still be usable, but dosing and monitoring should be individualized.
What about high-dose IV vitamin C – is that more dangerous for the kidneys?
High-dose intravenous vitamin C (often used in integrative cancer care) raises blood levels much higher than oral supplements. Understandably, patients and doctors worry about kidney safety.
The literature shows:
- There are rare case reports of oxalate nephropathy or acute kidney injury after massive IV vitamin C, usually in people who already had kidney problems.
- In patients with normal kidney function, pharmacokinetic studies suggest that only a small fraction (around 0.5% or less) of vitamin C is converted to oxalate, and most tolerate infusions well.
So again, context matters:
- For people with normal renal function, under proper medical supervision, high-dose IV vitamin C appears generally safe, though monitoring is still important.
- For people with pre-existing kidney disease, risks are higher and IV vitamin C should only be considered with great caution, if at all.
The right question is not “good or bad” – it’s “right for whom, and how?”
Medicine is rarely about simple yes/no answers.
Asking “Does vitamin C cause kidney stones?” is a bit like asking “Is fat bad?” or “Is exercise harmful?”
A more accurate way to think about it is:
- For whom?
- In what dose?
- For how long?
- In what overall health and lifestyle context?
For the average person with normal kidneys, reasonable vitamin C supplementation is:
- unlikely to cause kidney stones,
- and the potential benefits (immune support, antioxidant effects, collagen formation, etc.) often outweigh the small and uncertain risk.
For people with kidney disease or recurrent stones, vitamin C should simply be treated as:
- a powerful tool that requires professional guidance and appropriate doses,
- not as forbidden poison, and not as a harmless candy.
Conclusion: “Vitamin C causes kidney stones” is an oversimplified – and often misleading – statement
The myth that “vitamin C causes kidney stones” began with partial data and grew with dramatic headlines. When we review the full body of research:
- Some studies show no increased risk.
- Some show a modest increase in certain high-dose, long-term situations in men.
- The absolute risk increase is small, and many confounding factors are at play.
- For most people with normal kidneys, the overall risk from moderate vitamin C use is low.
So instead of being scared away from vitamin C completely, it is far more helpful to:
- understand your own kidney health,
- use balanced supplementation (not just mega-dosing one nutrient alone),
- maintain healthy hydration and diet,
- and work with a knowledgeable clinician if you have higher-risk conditions.
The real goal is not to find something perfect and risk-free—that doesn’t exist—but to minimize risk and maximize benefit, based on who you are.
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References
- Lawton, J. M., Conway, L. T., Crosson, J. T., Smith, C. L., & Abraham, P. A. (1985). Acute oxalate nephropathy after massive ascorbic acid administration. Archives of Internal Medicine, 145(5), 950–951.
https://doi.org/10.1001/archinte.145.5.950 - Wong, K., Thomson, C., Bailey, R. R., McDiarmid, S., & Gardner, J. (1994). Acute oxalate nephropathy after a massive intravenous dose of vitamin C. Australian and New Zealand Journal of Medicine, 24(4), 410–411.
https://doi.org/10.1111/j.1445-5994.1994.tb01477.x - Cossey, L. N., Rahim, F., & Larsen, C. P. (2013). Oxalate nephropathy and intravenous vitamin C. American Journal of Kidney Diseases, 61(6), 1032–1035.
https://doi.org/10.1053/j.ajkd.2013.01.025 - Curhan, G. C., Willett, W. C., Speizer, F. E., & Stampfer, M. J. (1999). Intake of vitamins B6 and C and the risk of kidney stones in women. Journal of the American Society of Nephrology, 10(4), 840–845.
https://jasn.asnjournals.org/content/10/4/840 - Gerster, H. (1997). No contribution of ascorbic acid to renal calcium oxalate stones. Annals of Nutrition and Metabolism, 41(5), 269–282.
https://doi.org/10.1159/000177954 - Curhan, G. C., Willett, W. C., Rimm, E. B., & Stampfer, M. J. (1996). A prospective study of the intake of vitamins C and B6, and the risk of kidney stones in men. Journal of Urology, 155(6), 1847–1851.
https://doi.org/10.1016/S0022-5347(01)66162-9 - Thomas, L. D. K., Elinder, C.-G., Tiselius, H.-G., Wolk, A., & Åkesson, A. (2013). Ascorbic acid supplements and kidney stone incidence among men: A prospective study. JAMA Internal Medicine, 173(5), 386–388.
https://doi.org/10.1001/jamainternmed.2013.2296 - Ferraro, P. M., Curhan, G. C., Gambaro, G., & Taylor, E. N. (2016). Total, dietary, and supplemental vitamin C intake and risk of incident kidney stones. American Journal of Kidney Diseases, 67(3), 400–407.
https://doi.org/10.1053/j.ajkd.2015.09.005 - Hoffer, L. J., Levine, M., Assouline, S., et al. (2008). Phase I clinical trial of i.v. ascorbic acid in advanced malignancy. Annals of Oncology, 19(11), 1969–1974.
https://doi.org/10.1093/annonc/mdn377 - Nauman, G., Gray, J. C., Parkinson, R., Levine, M., Paller, C. J., & Pendyala, L. (2018). Systematic review of intravenous ascorbate in cancer clinical trials. Antioxidants, 7(7), 89.
https://doi.org/10.3390/antiox7070089