Cats make their own vitamin C, but it’s time to rethink the idea that they don’t need any extra.

You’ve probably heard that cats don’t need extra vitamin C. But could a little extra still help?

In a 2026 study, monkeys given extra vitamin C showed fewer signs of aging in several organs. Let’s look at the research in cats and what we know about the risk of urinary stones.

Your cat’s food or supplements may already contain vitamin C. Read on for three things to check when giving supplements.

A Monkey Study Found a New Way Vitamin C Works

A team led by researchers at the Chinese Academy of Sciences published the study in Cell Metabolism in March 2026. As the body ages, iron can contribute to damage in the membranes around cells, a little like rusting.

The researchers focused on an enzyme involved in this damage. They found that vitamin C attaches directly to this enzyme and reduces its activity.

The older monkeys were already getting vitamin C in their regular food. The researchers gave them extra vitamin C for about 40 months. They then found fewer signs of cell damage and aging in several organs, including the kidneys.

Unlike cats, these monkeys cannot make their own vitamin C, so we still need to learn whether cats would benefit in the same way.

The kidney findings are one reason this study caught our attention at Greycoat Research. We’re hopeful about vitamin C’s potential to help slow kidney aging in cats.

A Study in Cats With CKD Used Several Antioxidants Together

Researchers have also studied cats with chronic kidney disease (CKD). Compared with healthy cats, they showed more signs of oxidative stress, which can damage cells.

The cats ate food with added vitamin C, vitamin E, and beta-carotene for four weeks. Afterward, signs of DNA damage decreased.

Several ingredients were given together. The study therefore cannot tell us what vitamin C did on its own, or whether the cats’ kidney disease improved.

How Oxalate Can Contribute to Stones

Some vitamin C can be broken down into oxalate. Oxalate can combine with calcium to form calcium oxalate stones.

In a long-term study in people, men who took high-dose vitamin C supplements were more likely to develop kidney stones. This link wasn’t clear in women or with vitamin C from food. Results in people may not be the same in cats.

A Four-Week Cat Study Found No Clear Increase in Oxalate

In one trial, 48 adult cats ate food containing different amounts of vitamin C for four weeks. There was no significant increase in oxalate in their urine.

The group with the highest intake averaged about 7.7 mg a day. It was the amount studied, not a recommended dose.

At Greycoat Research, our view is clear: we don’t consider increased urinary oxalate a major concern at the small amounts tested in this study. Vitamin C is already used in commercial cat foods.

This trial followed healthy cats for four weeks. If your cat has CKD or urinary stones, start with point 2 below.

Three Things to Check When Giving Supplements

Based on our experience advising cat owners, we believe nutritional care should start while cats are still healthy. Choosing ingredients that fit each cat’s health and diet is key.

We see vitamin C as one ingredient that may help the kidneys age more slowly. That’s why we recommend small amounts of vitamin C for healthy cats. Keep the following three points in mind when giving it.

1. Check What Your Cat Is Already Getting

Multivitamins and some joint supplements may already contain vitamin C. It may be listed as ascorbic acid or under a name that includes ascorbyl. Choose a low-dose vitamin C supplement and follow the feeding directions on the label.

2. If Your Cat Has Stones or CKD, Check With Your Vet

Take extra care if your cat has had calcium oxalate stones. At your cat’s veterinary visit, bring the product names and the amounts you give each day. Your vet can review the ingredients and amounts based on your cat’s kidney health and the type of stone involved.

3. Watch Your Cat’s Litter Box Habits

Straining to pee or making repeated trips to the litter box can be signs of urinary stones. So can blood in the urine. Have your vet check the cause, and let them know what food and supplements your cat is getting.

If your cat is passing little or no urine, seek emergency veterinary care right away.

It’s Time to Take Another Look at Vitamin C

Vitamin C is a familiar ingredient in cat food and supplements. Because cats make their own, extra vitamin C has often been seen as unnecessary.

Vitamin C may have more to offer our cats as they grow older. At Greycoat Research, we’re hopeful that this familiar nutrient could help their kidneys age more slowly.

Greycoat Research is here to help you care for your cat’s kidneys, starting while they’re healthy.

Explore Greycoat Research Kidney Care →

About the Author and Research Team

Alex Shin, Pharmacist | Greycoat Research

More than 20 years advising on medication use in animals

Consultations with owners of cats with kidney disease · Nutritional formulation advice

Greycoat Research works with veterinarians, pharmacists, and researchers in South Korea and Japan to study feline kidney health and nutrition.

Sources

1. Vitamin C’s mechanism and the long-term monkey study: Liu L, et al. Vitamin C inhibits ACSL4 to alleviate ferro-aging in primates. Cell Metabolism. 2026;38(4):673–693.e17.
2. Combined antioxidants in cats with renal insufficiency: Yu S, Paetau-Robinson I. Dietary supplements of vitamins E and C and β-carotene reduce oxidative stress in cats with renal insufficiency. Veterinary Research Communications. 2006;30(4):403–413.
3. Vitamin C intake and urinary oxalate in cats: Yu S, Gross KL. Moderate dietary vitamin C supplement does not affect urinary oxalate concentration in cats. Journal of Animal Physiology and Animal Nutrition. 2005;89:428–429.
4. Vitamin C intake and kidney stone risk in people: Ferraro PM, et al. Total, dietary, and supplemental vitamin C intake and risk of incident kidney stones. American Journal of Kidney Diseases. 2016;67(3):400–407.
5. Supplement ingredients and urinary stones: Minnesota Urolith Center, University of Minnesota. Are joint supplements “ok” for dogs and cats with uroliths?. 2025.
6. Vitamin C in a commercial cat food: Royal Canin. Feline Gastrointestinal: Ingredients and Guaranteed Analysis. Official product information. Accessed October 18, 2026.

Educational Disclaimer

This article is for educational purposes only and is not a substitute for professional veterinary advice, diagnosis, or treatment. It is not intended to diagnose, treat, cure, or prevent any disease.

Please consult your veterinarian before making changes to your cat’s diet, supplements, or care routine.