Vitamin C Side Effects

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Vitamin C is a water-soluble substance and therefore does not accumulate in the body. This accounts for the absence of any data on vitamin C toxicity per se. Vitamin C in itself is of low toxicity and has only minor adverse effects, such as diarrhea, nausea and other digestive disturbances.

These upsets are due to the osmotic withdrawal of water from the intestinal contents by the unabsorbed vitamin C in the gastrointestinal tract. Other physiologic disruptions due to high vitamin C levels include metabolic acidosis and altered levels of some coagulation factors such as prothrombin.

Image Credit: Pixelbliss / Shutterstock
Image Credit: Pixelbliss / Shutterstock

Urinary oxaluria

Vitamin C metabolism produces oxalate as a product. Some research suggests that vitamin C supplements may increase urinary oxalate concentrations, and double the risk of calcium oxalate kidney stones.

Drug interactions

Several drugs reduce vitamin C levels, such as contraceptive pills that contain estrogen, barbiturates and tetracyclines. Vitamin C also raises estrogen levels.

Regular aspirin intake above a certain frequency, such as 1000 mg every 6 hours, increases the urinary excretion of vitamin C and reduces its blood levels. Vitamin C causes higher serum levels of aspirin and other NSAIDs.

Vitamin C can inhibit the action of warfarin, and thus the dosage of warfarin requires to be monitored by the prothrombin time. It may also reduce the cardioprotective action of cholesterol-lowering drugs such as simvastatin and niacin, though the evidence is far from clear. Some large trials indicate that it does not affect the positive effects of these drugs.

It has been suggested that vitamin C use during cancer cell chemotherapy could diminish the efficacy of treatment by protecting tumor cells from destruction. Other studies, though, indicate that vitamin C exerts a possible protective effect on normal cells against the damage induced by radiotherapy or chemotherapy.

It has also been suggested that high doses of vitamin C could lead to oxidative damage by contributing to free radical production, but this has not been experimentally shown.

Laboratory tests

Tests such as serum bilirubin, serum creatinine and the guaiac test for the presence of occult blood depend upon the presence of reducing substances, and thus high levels of vitamin C can interfere with their interpretation.

Vitamin C and cardiovascular disease

A single study showed that vitamin C supplementation appeared to increase cardiovascular disease mortality in postmenopausal diabetic women, but this has never been confirmed.

Vitamin C and mineral absorption

Vitamin C may theoretically cause excessive iron absorption, but this is likely to be of significance only in those who have hereditary hemochromatosis and consume high doses of vitamin C.

When taken along with aluminum-containing antacids, vitamin C boosts aluminum absorption and therefore the risks of side effects.

Conditioned scurvy

Megadoses of vitamin C in pregnancy may cause rebound scurvy in the infant, due to the sudden drop in levels causing a relative deficiency of the vitamin in the baby’s blood after birth. Thus, doses above 1000 mg of vitamin C should be avoided in pregnancy unless on medical advice.

Dubious adverse effects

Other dubious effects, which have been raised over the years, but never been proven to exist, include:

  • reduction in vitamin b12 and copper levels in serum
  • erosion of dental enamel
  • allergy to vitamin c

Preventing the adverse effects of vitamin C

FNB-established upper levels are age-specific and are intended to prevent side effects. Precautions to prevent adverse reactions include:

  • adequate fluid intake to counter the diuretic effect of vitamin C supplements
  • avoiding vitamin C supplementation if you have hemochromatosis, sickle cell anemia, G6PD, or thalassemia
  • seeking medical advice before starting vitamin C supplementation, in case of renal disease or during chemotherapy
  • stopping the use of nicotine if planning to take vitamin C supplementation
  • stopping vitamin C supplements right before or after angioplasty


Further Reading

Last Updated: Apr 6, 2021

Dr. Liji Thomas

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.


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  1. Kushal Qanungo Kushal Qanungo India says:

    I had vitamin C poisoning due taking excess amla (20-25 dried  ones)(India gooseberry, which has the highest content of Vitamin C naturally).
    My symptoms were:
    1. Nausea and Vomiting 1st day
    2. Confusion 1st Day
    3. Stomach Bloating 5 Days
    4. Diarrhea 2nd Day Morning
    5. Fever for 5 days 100.4 deg F
    The above information may be used by doctors and general public at large.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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