Vitamin C is usually safe to take even at high dosages. However, people may experience mild side effects, such as digestive discomfort.

Vitamin C is an essential vitamin for the human body. It is an antioxidant, and it helps with a range of important processes, including lowering blood pressure, fighting inflammation, and creating collagen.

In this article, we look at the recommended upper limits of vitamin C intake, possible side effects of taking too much, and other warnings.

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It is usually safe to frequently eat foods high in vitamin C.

Frequently eating foods high in vitamin C should not lead to any health issues. Taking too much vitamin C through supplements can, however, cause side effects.

In adults, the recommended dietary allowance (RDA) of vitamin C is 90 milligrams (mg) for males and 75 mg for females.

Adults who take more than 2,000 mg of vitamin C per day may experience side effects.

When a person takes more than the recommended limit of vitamin C, they may experience mild digestive disturbances. These can occur if the vitamin C that the body does not absorb irritates the gastrointestinal tract.

Common mild side effects of too much vitamin C include:

  • diarrhea
  • nausea
  • stomach cramping
  • bloating
  • general abdominal discomfort

The body does not absorb all of the vitamin C that it gets from supplements.

For example, if a person takes 30–180 mg of vitamin C each day, their body absorbs about 70–90% of this vitamin. If a person takes more than 1 gram (g) of vitamin C per day, the body absorbs less than 50% of the vitamin, which reduces the risk of negative side effects. The excess leaves the body in the urine.

As vitamin C can cause unpleasant symptoms if a person takes too much, the Food and Nutrition Board have established “tolerable upper intake levels.”

According to the Office of Dietary Supplements (ODS), the upper limit for vitamin C intake in people aged 19 years and over is 2,000 mg in males and females. The limit remains the same for pregnant or breastfeeding women.

The upper daily vitamin C levels for children and infants are as follows:

  • 400 mg for infants aged 1–3 years
  • 650 mg for children aged 4–8 years
  • 1,200 mg for children aged 9–13 years
  • 1,800 mg for teenagers aged 14–18 years
  • 1,800 mg in pregnant or breastfeeding teenagers aged 14–18 years

There are exceptions to these limits, which only apply if a person’s doctor has not specified a different intake. Some people may have to take larger amounts of vitamin C for medical treatments.

Less commonly, people may experience severe side effects from taking too much vitamin C. Long term intake above the recommended levels increases the risk of these negative effects.

Possible health risks of taking too much vitamin C include:

Kidney stones

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Kidney stones are a possible consequence of too much vitamin C supplementation.

Doctors believe that too much vitamin C supplementation could result in a person excreting the compounds oxalate and uric acid in their urine. These compounds could lead to kidney stone formation.

The authors of a case study in the journal Kidney Internationalreported that a woman developed kidney stones after taking 4 g or more of vitamin C each day for 4 months.

However, researchers have not conducted any larger scale studies on vitamin C intake and kidney stone formation. They do know that people who have a history of kidney stones are more likely to form them if they take large amounts of vitamin C, according to the ODS.

Nutrient imbalances

Another concern regarding excessive vitamin C intake is that it can impair the body’s ability to process other nutrients.

For example, vitamin C may reduce the levels of vitamin B-12 and copper in the body.

The presence of vitamin C can also enhance iron absorption in the body, which could lead to excessively high levels.

Impair the effectiveness of niacin-simvastatin

Evidence suggests that taking vitamin C supplements may impair the body’s ability to increase high density lipoprotein (HDL) cholesterol in people taking the combination drug niacin-simvastatin. This drug combines the vitamin niacin with the statin simvastatin (Zocor), and people take it to treat high cholesterol.

Doctors consider HDL cholesterol the “good” cholesterol because it reduces the amount of harmful cholesterol in the blood.

If a person takes vitamin C supplements and niacin-simvastatin, they should talk to their doctor about ways to make each more effective. Doctors do not know whether vitamin C also affects the ability of other medicines similar to Zocor.

A person’s body cannot make vitamin C, so people need to eat enough foods that contain vitamin C to meet their daily needs. If someone is at risk of a vitamin C deficiency, they can take vitamin C supplements.

The ODS advise aiming for the following RDA of vitamin C each day:

1–3 years15 mg15 mg
4–8 years25 mg25 mg
9–13 years45 mg45 mg
14–18 years75 mg65 mg
19+ years90 mg75 mg

People who smoke should take 35 mg more vitamin C per day than those who do not smoke.

During pregnancy or when breastfeeding, women should get the following levels of vitamin C per day:

  • 14–18 years: 80 mg during pregnancy and 115 mg when breastfeeding
  • 19 years and older: 85 mg during pregnancy and 120 mg when breastfeeding

There is not enough research to suggest an RDA for vitamin C in those younger than 1 year of age. As a result, the ODS provide an “adequate intake,” which is the amount that is likely to be sufficient:

  • 40 mg for babies aged 0–6 months
  • 50 mg for infants aged 7–12 months
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A pregnant woman may wish to take a vitamin C supplement if they have trouble getting enough from their diet.

Some doctors advocate women taking vitamin C supplements when pregnant.

A literature review in the Cochrane Database of Systematic Reviews looked into the effects of vitamin C supplementation during pregnancy.

The authors examined 29 studies that included 24,300 pregnant women. There was insufficient evidence for them to conclude that vitamin C helped prevent problems during pregnancy, such as stillbirth, preterm birth, or preeclampsia.

However, pregnant women should try to get enough vitamin C through their daily diets when pregnant. Foods high in vitamin C include:

  • broccoli
  • kiwifruit
  • oranges
  • strawberries
  • tomatoes

If a woman has trouble meeting her daily requirements, she should talk to her doctor about supplementation.

Vitamin C has potentially harmful side effects if a person takes too many supplements. Usually, a person will not experience side effects if they eat a lot of foods containing vitamin C.

If a person suspects that their vitamin C intake may be causing side effects, they should talk to their doctor.