Can excessive intake of vitamin C (ascorbic acid) cause adverse effects?

Vitamin C Toxicity: Potential Adverse Effects of Excessive Intake

Yes, excessive intake of vitamin C (ascorbic acid) can cause adverse effects, though it is generally safe at recommended doses and even somewhat higher intakes. 1, 2

Safe Intake Levels and Upper Limits

• The Tolerable Upper Intake Level (UL) for vitamin C has been established at 2,000 mg/day for adults, which represents the highest daily intake unlikely to pose adverse health effects to most individuals 1, 2
• Recommended Dietary Allowances (RDAs) for vitamin C vary globally, ranging from 40-45 mg/day in some countries (UK, India) to 110 mg/day in European countries, with the US recommending 90 mg/day for men and 75 mg/day for women 1
• These variations reflect different health perspectives used to establish recommendations, from simply preventing deficiency to optimizing health benefits 1

Potential Adverse Effects of Excessive Vitamin C Intake

Gastrointestinal Effects

• The most common adverse effects of high vitamin C intake are gastrointestinal disturbances, including diarrhea and other gastrointestinal discomfort 1, 2
• These effects typically occur at doses exceeding the UL (2,000 mg/day) and are related to the osmotic effects of unabsorbed vitamin C in the intestinal tract 2

Kidney-Related Concerns

• High-dose vitamin C supplementation may increase the risk of kidney stone formation in susceptible individuals 3, 4
• Oxalate nephropathy (kidney damage from oxalate crystal deposition) has been reported in rare cases with excessive vitamin C intake 4, 5
• A fatal case of vitamin C-associated acute renal failure has been documented, with oxalate crystal deposition confirmed at autopsy 4

Special Populations at Risk

• Individuals with a history of kidney stones should exercise caution with vitamin C supplementation 3, 2
• People with iron overload conditions may experience adverse effects from high vitamin C intake due to enhanced iron absorption 3, 1
• Patients with glucose-6-phosphate dehydrogenase deficiency may experience hemolysis with high-dose IV vitamin C 5
• Patients with hemochromatosis should avoid vitamin C supplementation, especially during the iron depletion phase of treatment 1

Other Potential Concerns

• High-dose vitamin C can interfere with certain laboratory tests, potentially masking diagnoses 3, 5
• Hypernatremia has been reported with high-dose intravenous vitamin C therapy 5
• Vitamin C can cause glucometer errors in some cases 5

Clinical Applications and Monitoring

• For general health maintenance, obtaining vitamin C through consumption of fruits and vegetables (5 servings daily) is recommended rather than high-dose supplementation 6
• In specific clinical scenarios such as critical illness, burns, or sepsis, higher doses of vitamin C may be considered under medical supervision 1
• When high-dose vitamin C therapy is used, monitoring for adverse effects is warranted, particularly in patients with pre-existing kidney disease or risk factors for complications 5

Conclusion for Clinical Practice

When advising patients about vitamin C intake:

• Encourage obtaining vitamin C through dietary sources when possible 6
• Inform patients that supplementation within the RDA range (75-110 mg/day) is generally safe 1
• Caution against exceeding the UL of 2,000 mg/day without medical supervision 1, 2
• Identify patients at higher risk for adverse effects (kidney stone formers, iron overload conditions, G6PD deficiency) and advise accordingly 3, 1, 5