What are the disadvantages of taking vitamin C tablets?

January 9, 2026 •

3 min read

While vitamin C is an essential nutrient vital for immune function and overall health, high-dose supplementation can lead to adverse effects. The body's inability to absorb excessive amounts of this water-soluble vitamin can lead to a range of issues, from minor digestive upset to more serious health complications.

Quick Summary

Excessive intake of vitamin C tablets can cause side effects like nausea, diarrhea, and abdominal cramps. It may also increase the risk of kidney stones, affect specific medical conditions, and interact with certain medications. Most dietary needs are met through food.

Key Points

Gastrointestinal Distress: High doses of vitamin C can cause digestive issues such as nausea, diarrhea, and stomach cramps as the body cannot absorb large quantities.
Increased Kidney Stone Risk: Excessive vitamin C intake can increase urinary oxalate levels, raising the risk of calcium oxalate kidney stone formation, particularly in susceptible individuals.
Interference with Medications: High-dose vitamin C supplements can interact with prescription drugs like blood thinners (warfarin) and cholesterol medications, potentially reducing their effectiveness.
Iron Overload Concerns: For people with hemochromatosis, a condition causing excess iron, vitamin C supplements can exacerbate the problem by increasing iron absorption, leading to tissue damage.
Unnecessary for Most Individuals: Most healthy individuals can meet their vitamin C needs through a balanced diet, making high-dose supplementation unnecessary and potentially risky.

Gastrointestinal Distress and Common Side Effects

One of the most immediate and common disadvantages of taking high doses of vitamin C tablets is gastrointestinal distress. The body can only absorb a limited amount of vitamin C at a time, so excess amounts are simply excreted. For oral supplements, this often leads to unwanted digestive symptoms. Doses exceeding 2,000 mg per day are frequently associated with these side effects.

Nausea and vomiting: High concentrations of ascorbic acid can irritate the stomach lining, leading to feelings of sickness.
Diarrhea: Unabsorbed vitamin C remaining in the digestive tract can cause an osmotic effect, pulling water into the colon and resulting in diarrhea.
Abdominal cramps and bloating: Along with diarrhea, excessive vitamin C can cause general discomfort, cramping, and flatulence.
Heartburn: For some individuals, a high intake of ascorbic acid can increase stomach acid and lead to heartburn.

Increased Risk of Kidney Stones

One of the most serious disadvantages associated with long-term, high-dose vitamin C supplementation is an increased risk of kidney stones. This is particularly concerning for individuals with pre-existing kidney conditions or a history of kidney stones. Vitamin C is metabolized into oxalate, which is then excreted through the urine. Excess oxalate can bind with calcium to form calcium oxalate crystals, the most common type of kidney stone. Studies have shown that men who take 1,000 mg or more of supplemental vitamin C per day have a significantly higher risk of developing kidney stones.

Nutrient Imbalances and Medication Interactions

High doses of vitamin C can interfere with the body's balance of other essential nutrients and interact with certain medications, potentially leading to complications. These interactions are often overlooked by individuals self-medicating with supplements.

Iron overload (hemochromatosis): Vitamin C enhances the absorption of nonheme iron, the type found in plant-based foods. While beneficial for those with iron deficiency, this can be dangerous for people with hemochromatosis, a condition causing excessive iron accumulation. In severe cases, this can lead to life-threatening tissue damage.
Medication interference: Vitamin C can interact with several types of medication, potentially reducing their effectiveness. This includes blood-thinning medication like warfarin, cholesterol-lowering drugs like statins, and chemotherapy.
Interference with lab tests: Very high levels of vitamin C can interfere with certain medical tests, such as blood glucose screenings or stool tests for hidden blood, leading to inaccurate results.

Rebound Scurvy in Infants

Though uncommon, excessive intake of vitamin C by pregnant mothers can lead to a condition known as "rebound scurvy" in newborns. The infant's body, accustomed to a high level of vitamin C while in the womb, can experience a sudden deficiency after birth, as their intake from external sources drops.

Supplementation vs. Dietary Intake: A Comparison


Feature	Vitamin C Tablets (High Dose)	Dietary Vitamin C (Whole Foods)
Absorption	Limited absorption at high doses; excess is excreted.	Regulated and more efficient absorption by the body.
Risk of Side Effects	Higher risk of gastrointestinal issues (nausea, diarrhea) and kidney stones, especially over 2,000 mg/day.	Minimal to no risk of toxicity or side effects from food sources.
Nutrient Balance	Can interfere with the balance and absorption of other nutrients like iron.	Part of a balanced nutritional profile, includes other vitamins and minerals.
Drug Interactions	Potential interactions with a range of medications, including chemotherapy and anticoagulants.	Very low risk of interactions with medication.
Overall Health Value	Often unnecessary for healthy individuals; no proven benefits for many conditions.	Contributes to a generally healthier lifestyle and provides a broader spectrum of nutrients.

Conclusion: Prioritizing Food Over Supplements

The disadvantages of taking high-dose vitamin C tablets are considerable and range from simple gastrointestinal discomfort to more serious risks, including kidney stone formation, nutrient imbalances, and medication interference. For the vast majority of healthy adults, a balanced diet rich in fruits and vegetables provides more than enough vitamin C, without the associated risks of excessive supplementation. The body naturally regulates its absorption of vitamin C from food more efficiently, making dietary intake a safer and more effective option. It is crucial to consult a healthcare professional before starting any high-dose vitamin C regimen, especially for those with pre-existing health conditions or who are taking other medications. For those seeking general wellness, focusing on dietary sources remains the wisest choice.

Note: For official dietary guidelines, consider consulting sources like the National Institutes of Health (NIH).

Frequently Asked Questions

The Tolerable Upper Intake Level (UL) for adults is 2,000 mg per day. Consuming more than this amount increases the risk of side effects like gastrointestinal problems and kidney stones.

Yes, high doses of vitamin C can increase the risk of kidney stones, particularly in individuals with a history of them, by increasing the excretion of oxalate in the urine.

Yes, high doses of vitamin C can interact with certain medications, including blood thinners (warfarin), statins, niacin, and some chemotherapy drugs, which can reduce their efficacy.

For most people, getting vitamin C from a balanced diet of fruits and vegetables is safer and more effective. The body absorbs dietary vitamin C more efficiently, and there is no risk of toxicity from food sources.

Common side effects from excessive vitamin C include diarrhea, nausea, heartburn, stomach cramps, and headaches.

No, they are not necessary for most people. The majority of individuals can get sufficient vitamin C from their diet. Supplements are only needed when a deficiency is diagnosed or for specific medical reasons under a doctor's supervision.

Excessive vitamin C intake by a pregnant mother can, in rare cases, cause rebound scurvy in the newborn, as the baby's body becomes accustomed to high levels and then experiences a sharp drop after birth.