Vitamin C side effects
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Common Side Effects of Vitamin C Supplementation
Vitamin C is generally considered safe for most people, especially at typical dietary or supplemental doses. When administered intravenously at high doses, most reported side effects are minor. These include lethargy or fatigue, changes in mental status, and irritation or inflammation of the veins (phlebitis) at the injection site. Such minor side effects were observed in a small proportion of patients receiving high-dose intravenous vitamin C, with lethargy/fatigue being the most common complaint .
Serious and Rare Adverse Effects of High-Dose Vitamin C
While most people tolerate vitamin C well, high doses—especially when given intravenously—can cause more serious side effects in certain individuals. These include:
- Oxalate nephropathy and kidney stones: High doses can increase the risk of kidney damage or kidney stones, particularly in people with pre-existing kidney problems 15.
- Hemolysis in G6PD deficiency: People with glucose-6-phosphate dehydrogenase (G6PD) deficiency are at risk of red blood cell breakdown (hemolysis) when given high-dose vitamin C 12.
- Hypernatremia: Elevated sodium levels in the blood have been reported in some cases .
- Glucometer errors: High vitamin C levels can interfere with some blood glucose meters, leading to inaccurate readings .
Safety in Critically Ill and General Populations
In studies involving critically ill patients, intravenous vitamin C did not show an increased risk of adverse effects compared to placebo. No significant difference in the rate of adverse events was found between those receiving vitamin C and those receiving placebo in randomized controlled trials 14. Most studies report that vitamin C is well tolerated, with no adverse effects noted in several clinical trials .
Special Populations and Precautions
Certain groups should exercise caution with high-dose vitamin C:
- Patients with kidney impairment: They are at higher risk for oxalate nephropathy and kidney stones 125.
- Individuals with G6PD deficiency: They are at risk for hemolysis and should avoid high-dose vitamin C 12.
- Patients with chronic or untreatable conditions: Physicians should ask about vitamin C use and monitor for unexpected side effects or drug interactions .
Vitamin C Deficiency and Neuropsychiatric Effects
On the other hand, vitamin C deficiency can also have side effects, particularly affecting mood and cognitive function. Deficiency has been linked to depression and cognitive impairment, even before the physical symptoms of scurvy appear . These neuropsychiatric effects highlight the importance of maintaining adequate vitamin C levels.
Conclusion
Vitamin C is generally safe for most people, even at high doses, but certain individuals—especially those with kidney problems or G6PD deficiency—are at risk for serious side effects such as kidney stones and hemolysis. Most side effects are minor and infrequent. Physicians should be aware of these risks and monitor susceptible patients accordingly. Maintaining adequate vitamin C levels is important for both physical and mental health, but excessive supplementation should be approached with caution in at-risk groups 12345.
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