7 Negative Side Effects of a Vitamin C Overdose

No, vitamin C can't kill you. But taking too much vitamin C may cause temporary side effects.
Image Credit: Jackyenjoyphotography/Moment/GettyImages

Vitamin C is an essential nutrient that supports your immune system, helps your body absorb iron and promotes growth and development. But while conventional wisdom may suggest that it's good to load up on the nutrient, that's not always the case. So, can you overdose on vitamin C?

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First things first, here's how much vitamin C adults should eat per day, according to the Mayo Clinic:

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But overdosing on vitamin C is possible, per the Mayo Clinic. Though the nutrient is water-soluble (meaning your body can pass excess vitamin C through your urine), you may not be able to process megadoses fast enough to avoid side effects. As a result, you can experience temporary symptoms of vitamin C overdose.

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It's best to get vitamin C from plant sources (like citrus fruits, berries and peppers) rather than supplements, according to the Mayo Clinic. This will help you avoid vitamin C overdose symptoms while still ensuring you get enough of the nutrient.

Still, to help you determine if too much vitamin C is the source of your discomfort, here are the vitamin C side effects to be aware of.

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How Many Milligrams of Vitamin C Is Too Much?

According to the Mayo Clinic, adults shouldn’t take more than 2,000 milligrams of vitamin C per day.

But if you check the label of vitamin C supplements, you may notice that some contain more than the recommended daily dose. And indeed, taking megadoses like 3,000 or 6,000 milligrams of vitamin C is too much.

1. Digestive Issues

Gastrointestinal discomfort is common if you overdose on vitamin C, according to the Mayo Clinic. Symptoms may include:

  • Diarrhea
  • Nausea
  • Vomiting
  • Heartburn
  • Stomach cramps

Remember, this is typically only the case if you have more than 2,000 to 3,000 milligrams of the vitamin per day, per the Mayo Clinic. Sticking to the recommended daily dose will help you avoid these symptoms.

Can Vitamin C Cause Muscle Spasms?

There's no evidence to show vitamin C is linked to muscle spasms. However, taking too much of the nutrient can lead to stomach cramping, per the Mayo Clinic.

2. Headaches

Taking too much vitamin C can cause headaches, according to the Mayo Clinic.

Again, vitamin C headaches typically occur when you exceed doses of 2,000 to 3,000 milligrams. So if you notice that supplements like Emergen-C are causing headaches, it's likely because you're overloading on the nutrient.

Does Vitamin C Help With Headaches?

We know vitamin C can cause headaches, but perhaps you’ve also heard that vitamin C is good for headaches. While there’s no research that establishes vitamin C as a fix for head pain, it is possible to experience other symptoms if you don’t get enough of the nutrient.

Per the U.S. National Library of Medicine, a vitamin C deficiency can cause symptoms like:

  • Anemia
  • Bleeding gums
  • Decreased ability to fight infection and heal wounds
  • Dry, splitting hair
  • Joint pain

3. Flushing

If you overdose on vitamin C, another common symptom is flushed skin, according to the Mayo Clinic.

Remember, sticking to the appropriate daily dose of the nutrient can help you avoid this and other side effects.

4. Kidney Stones

Taking too much vitamin C can cause kidney stones for some people, according to the Mayo Clinic.

Here's why: Your body breaks down vitamin C into a substance called oxalate. Some oxalate is secreted in urine, however, high urinary oxalate levels may start to form kidney stones, per a January 2022 StatPearls article.

High vitamin C intake is associated with an increased risk of oxalate kidney stones, which are one of the most common types of kidney stones, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

People with a history of kidney disease or kidney stones are at higher risk for this side effect, according to Harvard Health Publishing, as these conditions may mean you can overdose on vitamin C more easily. As a result, anyone with underlying kidney problems shouldn't take more than 1,000 milligrams of the nutrient a day.

Tip

Talk to your doctor before trying a vitamin C supplement to make sure it’s safe for you (especially if you have an underlying condition or take medication), per the Mayo Clinic. The FDA doesn’t require supplements to be proven safe or effective before they’re sold, so there’s no guarantee that what you take is safe or effective.

5. Iron Overload

Overdosing on vitamin C can be particularly dangerous for people with hemochromatosis, a genetic condition that causes high levels of iron in your blood, according to the Harvard T.H. Chan School of Public Health.

That's because vitamin C helps your body absorb iron, per the Mayo Clinic. While this is a good thing if you don't already have elevated iron levels, it can cause problems if you do.

According to the NIDDK, untreated hemochromatosis can cause damage to your liver, heart, pancreas, endocrine glands and joints.

Vitamin C and Your Liver

Is vitamin C good for your liver? Well, getting adequate doses of vitamin C is typically good for the liver and other organs, as the nutrient is essential for your wellbeing, per the Mayo Clinic. In fact, vitamin C is in part synthesized by the liver, according to April 2016 research in ​Oral Diseases​.

That said, if you have a chronic condition that can affect your liver (like hemochromatosis), it’s best to avoid doses higher than 1,000 milligrams a day, per Harvard Health Publishing.

When in doubt, talk to your doctor about whether too much vitamin C is bad for your condition, like if you have fatty liver disease.

6. Dizziness

If you overdose vitamin C, you may experience dizziness, according to the ​StatPearls​ article.

However, it's worth noting that this side effect was linked to vitamin C doses are administered through an IV.

7. Insomnia

Insomnia is another potential vitamin C overdose symptom, according to Harvard Health Publishing.

Taking a high dose of the nutrient — which is typically only the case if you use supplements — can keep you up at night while your body processes the excess vitamins.

What Happens If You Take 6,000 Milligrams of Vitamin C?

Remember, vitamin C is water-soluble, meaning you excrete it through your urine, per the Mayo Clinic. Still, too much vitamin C can hurt you temporarily by causing symptoms like those outlined above. As a result, taking megadoses like 6,000 milligrams of vitamin C is not considered safe or necessary.

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