Why You Should Never, Ever Take More Than The Recommended Amount Of Vitamin C

If you take vitamin C supplements, you may want to take a closer look at your dosage.
Taking excess amounts of vitamin C won't provide any benefits — and it can be dangerous.
Peter Dazeley via Getty Images
Taking excess amounts of vitamin C won't provide any benefits — and it can be dangerous.

If you take vitamin C supplements, you may want to take a closer look at your dosage. Some people are overdoing it thanks to sketchy advice they’re seeing online, and developing uncomfortable side effects like nausea, headaches or heartburn — and, in extreme cases, painful kidney stones.

Last week, a TikTok influencer battling colon cancer shared that she developed kidney stones after she’d been taking very high doses of vitamin C in an effort to boost her immunity and combat the cancer. She said she had been ingesting 50 g of vitamin C every day, she said, which equals a whopping 50,000 mg. The recommended daily intake for women is 75 mg.

After seeing the video on TikTok, Dr. Ashley Winter, a board-certified urologist and chief medical officer at Odela Health, posted to X, formerly known as Twitter, to break down why taking too much vitamin C isn’t only unhelpful — it can also be dangerous.

“Excess vitamin C in your diet doesn’t DO anything for your immune system because you just pee it out. And in your pee, the vitamin C becomes Oxalate, which is one of the major causes of KIDNEY STONES! YOU ARE LITERALLY FOLLOWING A DAMN KIDNEY STONE RECIPE,” Winter wrote.

Supplement needs can vary, so it’s best to talk with a doctor to figure out what is best for you instead of going off the assumption that you need more of a vitamin for your health. And in the case of vitamin C, there can be such a thing as overdoing it.

Vitamin C is a water-soluble vitamin that’s found in citrus fruits (think: oranges and grapefruit), cruciferous vegetables (such as cauliflower and kale) and potatoes. It plays an important role in the growth of our skin, bones and connective tissue. It’s also a powerful antioxidant, meaning it protects our cells from free radical damage. At a normal dose, which is 75 mg a day for women and 90 mg a day for men, vitamin C supports healthy immune function.

You don’t want to have low levels of vitamin C, but the vast majority of people don’t. Too little vitamin C can cause issues like easy bruising and dry, splitting hair. Serious vitamin C deficiencies cause scurvy, a disease that can lead to fatigue, anaemia and joint pain along with bleeding gums and loosened teeth. However, it’s not common — in the United States, about 7.1% of the population may develop any kind of vitamin C deficiency according to the Cleveland Clinic, and the incidence of extreme deficiency that leads to scurvy is rare.

On the flip side, boosting vitamin C levels too high also brings issues. Because it’s water-soluble, vitamin C is not stored in your body. Your kidney processes it and you pee it out, Winter said. This means two things. One: High amounts of vitamin C won’t do anything for your health because it’ll just get excreted in your urine. Two: It can be risky. As your kidneys process an overflow of vitamin C, oxalate, one of the main causes of kidney stones, forms and accumulates. Over time, that oxalate can crystallise and turn into kidney stones, said Winter. Your kidneys will essentially have to work overtime and there are going to be health consequences, she added.

Some of the milder signs you may be ingesting too much vitamin C include gastrointestinal problems like nausea, diarrhoea, heartburn and vomiting. Plus, the higher your dose, the greater your risk of kidney stones. Kidney stones can block urine flow out of your kidneys and be incredibly painful. While some people can pass kidney stones naturally, others will need surgery to recover. In severe cases, too much vitamin C can even lead to kidney failure.

“High doses of vitamin C don’t really ‘help’ that much,” said Dana Ellis Hunnes, a clinical dietitian, assistant professor at UCLA Fielding School of Public Health, and author of “Recipe for Survival.”

Vitamin C supplements probably don’t boost your immune system, anyway.

Hunnes said people are often looking to be healthy or healthier in general, and supplements are typically marketed as a relatively cheap way to achieve that. While vitamins and minerals are essential for several body functions, it’s important not to get carried away.

“Just because a little bit of something is good doesn’t mean a lot of something is better,” she said.

Winter said she started to see an uptick in patients taking extreme quantities of supplements like vitamin C during the pandemic, when many people were looking for natural ways to boost their immune system. (Data shows vitamin C sales soared during 2020.) It doesn’t help that you can find vitamin C products everywhere, with many claiming to enhance your health or boost your immune system.

Despite the widespread popularity and accessibility of such products, there’s really no convincing evidence to support the belief that high doses of vitamin C do anything for your immune system, said Winter. “There’s this conflation between taking normal vitamin C, correcting scurvy, and using excess quantities of vitamin C for this quote-unquote immune boost,” she said.

So, how much vitamin C should you take?

As mentioned above, the recommended daily intake of vitamin C in adults is 75 mg for women and 90 mg for men. Most people get more than enough vitamin C by consuming fruits and vegetables or by taking a multivitamin and don’t need to take any vitamin C supplements, Winter said. Eating fruits and vegetables like oranges, strawberries, Brussels sprouts and broccoli, is the best way to get your daily dose of vitamin C. Not only are these foods a good source of the vitamin, but the calcium in them helps to inhibit the production of kidney stones, according to Harvard Health.

That said, vitamin C supplements are recommended for certain health conditions that cause intestinal malabsorption problems or to counteract the side effects from some medications, like methenamine. Even in these situations, which should be closely monitored by a health care provider, a person probably wouldn’t need more than a 500 mg supplement, Winters said.

If you do have a concern about the right amount of vitamin C for your needs, reach out to your physician. The upper limit for adults is 2,000 mg a day, but that doesn’t mean it’s worth getting close to the limit. Anything more than the recommended daily allowance or perhaps even up to two or three times that amount doesn’t really do you any good anyway, said Hunnes. “You’re best to get the daily requirement, maybe slightly more, and call it a day,” she said.