What happens if I take 1000mg of vitamin C daily?

October 23, 2025 •

4 min read

The human body does not produce vitamin C, so it must be obtained from diet or supplements. For adults, the Recommended Dietary Allowance (RDA) is significantly lower than a 1000mg dose. Therefore, taking a 1000mg supplement daily is a much higher intake than what is generally considered necessary for most people's basic needs.

Quick Summary

Taking a 1000mg vitamin C supplement daily offers potential benefits like enhanced antioxidant and immune support, but also increases the risk of side effects such as digestive issues and potential oxalate elevation. The body's absorption efficiency decreases at higher doses, meaning much of the supplement is excreted. For most, a balanced diet can meet requirements, making high-dose supplementation often unnecessary.

Key Points

Decreased Absorption: The body's absorption of vitamin C decreases significantly at higher doses, with a large portion of a 1000mg dose being excreted.
Potential Digestive Issues: Common side effects of a 1000mg daily intake include stomach pain, diarrhea, and nausea due to unabsorbed vitamin C in the gastrointestinal tract.
Risk of Kidney Stones: Regular high intake of vitamin C can increase urinary oxalate excretion, potentially leading to kidney stone formation, especially in susceptible individuals.
Exacerbates Iron Overload: Individuals with hemochromatosis, an iron absorption disorder, risk tissue damage from high vitamin C intake due to enhanced iron absorption.
Dietary Alternatives Are Sufficient: The recommended daily intake for most adults is well below 1000mg and can be easily met by consuming a variety of fruits and vegetables.
Immunity and Antioxidant Benefits: A 1000mg dose does provide enhanced antioxidant activity and may offer modest immune benefits, such as reduced cold duration.
Specific Conditions Require Caution: Those with chronic kidney or liver disease should consult a doctor, as they are advised to limit vitamin C intake to a specific level or less.

High-Dose Vitamin C: Benefits and Absorption Realities

Before considering a daily 1000mg vitamin C supplement, it is important to understand that information presented here is for general knowledge and should not be taken as medical advice. Always consult with a healthcare provider before starting any new supplement regimen.

While vitamin C is a crucial nutrient and a potent antioxidant, the effects of a 1000mg daily dose can be different from the outcomes many expect. Because vitamin C is water-soluble, the body excretes excess amounts in the urine rather than storing it. For healthy individuals, this means much of a high dose is not utilized, and absorption rates decrease dramatically as intake increases. This is a key reason why consuming a 1000mg dose is fundamentally different from receiving a smaller, more absorbable amount through food.

Potential Benefits of a Daily 1000mg Intake

Enhanced antioxidant activity

Vitamin C is a powerful antioxidant that helps protect the body's cells from oxidative stress and damage caused by free radicals. Taking a higher dose can boost the body's antioxidant defenses, potentially offering greater protection against chronic diseases linked to oxidative stress. This enhanced antioxidant status can be particularly beneficial for individuals exposed to high levels of pollution or oxidative stress.

Strengthened immune function

Many people take high doses of vitamin C to support their immune system. Some studies suggest that while it may not prevent the common cold, consistent high-dose intake might shorten its duration and reduce the severity of symptoms. This immune-boosting effect is attributed to vitamin C's role in encouraging the production and enhancing the function of white blood cells.

Improved skin health and wound healing

As a crucial cofactor for collagen synthesis, vitamin C is essential for maintaining healthy skin, blood vessels, and connective tissues. A higher daily intake may support collagen production, which helps with wound healing and maintaining skin elasticity. This can be particularly relevant for those with impaired wound healing or looking to improve skin appearance.

Increased non-heme iron absorption

Vitamin C significantly enhances the absorption of non-heme iron, the type found in plant-based foods. This can be beneficial for individuals with low iron levels or those following vegetarian or vegan diets. Taking a supplement alongside meals can aid in converting this iron into a more easily absorbed form.

Potential Risks and Side Effects of a Daily 1000mg Intake

Digestive upset

The most common side effect of high vitamin C intake is digestive distress. Since the body’s absorption rate declines with larger doses, unabsorbed vitamin C can draw water into the intestines, leading to symptoms such as:

Diarrhea
Nausea and stomach cramps
Heartburn

Increased risk of kidney stones

High vitamin C intake can elevate the amount of oxalate excreted in the urine. Oxalate can bind with minerals to form crystals, potentially leading to kidney stones. This risk is especially pertinent for individuals with a history of kidney issues, and high doses are particularly cautioned against for this group.

Concerns for individuals with certain health conditions

For those with specific health concerns, a 1000mg dose can pose particular risks. Individuals with hereditary hemochromatosis, a disorder of iron absorption, should be especially cautious, as enhanced iron absorption from high vitamin C intake can cause iron overload and tissue damage. Additionally, high doses can interact with certain medical tests, such as blood sugar screenings.

Comparative Analysis: 1000mg vs. Recommended Dietary Allowance (RDA)


Feature	1000mg Daily Dose	RDA (e.g., 90mg for adult males)
Absorption Efficiency	Poor; less than 50% absorbed, with the rest excreted.	High; 70-90% absorbed at typical dietary levels.
Bodily Utilization	High amounts are quickly flushed from the system and not fully utilized.	More fully utilized by the body to support essential functions.
Risk of Side Effects	Higher risk of digestive issues like diarrhea, and potential for kidney stone formation.	Minimal to no risk of side effects from food-based vitamin C.
Main Goal	Often taken for perceived "super-dosing" effects, immune system boosts, or specific conditions.	Prevents deficiency diseases like scurvy and maintains basic health.
Source	Typically sourced from concentrated supplements.	Primarily obtained through a balanced diet of fruits and vegetables.

Conclusion

While a 1000mg daily dose of vitamin C might seem beneficial for its enhanced antioxidant and immune-supporting potential, it is not a universally necessary or efficient strategy. For most healthy adults, a balanced diet provides sufficient vitamin C to prevent deficiency and support foundational health. The body's absorption efficiency significantly declines at a 1000mg dose, meaning a large portion is simply wasted and excreted. Moreover, for individuals with pre-existing conditions like a history of kidney stones or hereditary hemochromatosis, this high dose can present specific risks. It is always advisable to consult a healthcare professional to determine if high-dose supplementation is appropriate for your individual needs. For comprehensive health and wellness, focusing on nutrient-dense foods remains the most reliable and safest approach.

Dietary Reference Intakes for Vitamin C

Frequently Asked Questions

No, while generally safe for most healthy adults, a daily 1000mg dose can cause side effects like digestive upset. It poses specific risks for individuals with a history of kidney stones or certain conditions like hereditary hemochromatosis.

Since vitamin C is water-soluble, any amount not absorbed by the body is simply excreted in the urine. At doses of 1000mg, the absorption rate decreases significantly, so a large portion of the vitamin is wasted.

In some susceptible individuals, a high intake of vitamin C can increase urinary oxalate levels, which is a key component of certain kidney stones. The risk is elevated for those with a history of kidney stones.

Benefits of higher doses, like 1000mg, include enhanced antioxidant protection, increased non-heme iron absorption, and potentially reduced duration of cold symptoms. However, for most healthy individuals, the amount gained from a high dose is often minimal.

For most people, obtaining vitamin C from whole foods like fruits and vegetables is the best approach. It ensures better absorption and provides other beneficial nutrients. Supplements are typically recommended only if dietary intake is insufficient or for specific medical reasons.

The most common side effects are gastrointestinal and can include nausea, diarrhea, stomach cramps, and heartburn.

The Recommended Dietary Allowance (RDA) for adult men is 90mg, and for adult women, it's 75mg. The tolerable upper intake level (UL) is 2000mg, though some experts advise caution below this level.