What will happen if I take 1000mg of vitamin C daily?

October 24, 2025 •

5 min read

According to the NIH, the tolerable upper intake level (UL) for vitamin C in adults is 2,000 mg per day. This guide explores what will happen if I take 1000mg of vitamin C daily, including potential benefits, common side effects, and how it compares to the daily recommendations.

Quick Summary

Taking a 1000mg vitamin C supplement is a higher dose than recommended, though it remains below the daily safety limit for most adults. Excess amounts are typically excreted in urine, but can cause digestive issues. The additional benefits over a balanced diet are often minimal for healthy individuals. Individuals with pre-existing health conditions should exercise caution.

Key Points

Excretion of Excess: Your body is water-soluble, so excess vitamin C from a 1000mg dose is mostly excreted through urine, not stored.
Potential Digestive Issues: High doses can trigger gastrointestinal discomfort, including diarrhea, nausea, and stomach cramps.
Kidney Stone Risk: Individuals with a history of kidney stones may face an increased risk from large amounts of vitamin C.
Minimal Added Benefit for Healthy People: For most healthy adults, a 1000mg supplement offers little proven benefit beyond the immune support and antioxidant effects derived from a balanced, vitamin C-rich diet.
Important for At-Risk Individuals: Those with chronic kidney disease, hemochromatosis, or G6PD deficiency should use caution with high-dose vitamin C.
Consult a Healthcare Provider: It is advisable to consult a healthcare provider before starting long-term, high-dose supplementation, especially if you have pre-existing health conditions.

Understanding the Recommended Intake vs. 1000mg

For most healthy adults, the Recommended Dietary Allowance (RDA) for vitamin C is 90 mg for men and 75 mg for women. This is a far cry from the 1000mg commonly found in supplements. The reason for this significant difference is that the RDA is the amount needed to prevent deficiency diseases like scurvy, while 1000mg is a 'megadose' intended to provide additional, often unproven, benefits. The body is highly efficient at absorbing vitamin C from food, but absorption from supplements decreases as the dose increases. The tolerable upper intake level (UL), the maximum daily intake unlikely to cause adverse effects, is 2,000 mg for adults. Therefore, taking 1000mg falls within the safe range for most people, but it's important to understand the implications.

Why Do People Take High-Dose Vitamin C?

Many people turn to high-dose vitamin C supplements for a variety of reasons, fueled by popular belief and historical claims, though some remain unsubstantiated.

Immune Support: Vitamin C is crucial for immune function, but research shows that a megadose does not prevent the common cold in the general population. It might, however, slightly reduce the duration of cold symptoms, particularly in athletes or those under extreme physical stress.
Antioxidant Power: As a potent antioxidant, vitamin C helps protect cells from damage caused by free radicals. A 1000mg dose significantly increases antioxidant levels, but whether this offers a tangible health advantage over a normal diet is debated.
Collagen Synthesis: Vitamin C is essential for producing collagen, a protein that maintains healthy skin, cartilage, tendons, and blood vessels. Higher doses might theoretically support this process, aiding in wound healing and skin health.
Iron Absorption: Vitamin C enhances the absorption of non-heme iron (from plant sources), which is particularly beneficial for those with iron deficiencies or following a meat-free diet.

Potential Side Effects and Health Risks

While 1000mg is below the 2000mg UL, it can still cause side effects, especially with long-term use. Since vitamin C is water-soluble, your body will excrete the excess, but not without potentially causing some issues.

Digestive Distress

The most common side effects are gastrointestinal. Taking large amounts of vitamin C can lead to:

Diarrhea
Stomach cramps and bloating
Nausea and heartburn

Kidney Stones

For individuals with a history of kidney stones, or those prone to them, taking more than 1000mg daily can increase the risk of forming kidney stones. This is because the body converts excess vitamin C into oxalate, which can contribute to stone formation.

Interference with Other Health Conditions

Certain medical conditions warrant caution with high vitamin C intake:

Chronic Kidney Disease: Too much vitamin C can increase oxalate excretion, posing a risk of kidney failure in those with impaired kidney function.
Hemochromatosis: Individuals with this iron absorption disorder should be cautious, as vitamin C enhances iron absorption and could exacerbate their condition.
G6PD Deficiency: This metabolic deficiency can lead to red blood cell breakdown (hemolytic anemia) with very high vitamin C doses, though this is rare with oral intake.

Potential for Rebound Scurvy

Some anecdotal evidence suggests that stopping high-dose supplementation abruptly could potentially lead to 'rebound scurvy', where the body, adapted to high intake, experiences temporary deficiency symptoms. This is not a scientifically established phenomenon in the same way as withdrawal from a stored nutrient, but it's a concern for some long-term users.

Comparison Table: RDA vs. 1000mg Vitamin C Supplement


Feature	Recommended Dietary Allowance (RDA)	1000mg Supplement (Megadose)
Typical Daily Dose	75-90 mg for adults	1000 mg
Primary Source	A balanced diet rich in fruits and vegetables.	Dietary supplement in tablet, capsule, or powder form.
Absorption	Highly efficient absorption from food sources.	Absorption efficiency decreases as dosage increases.
Primary Purpose	Prevents vitamin C deficiency (scurvy) and supports basic health functions.	Aims to provide additional benefits beyond basic needs, like enhanced antioxidant or immune support.
Side Effect Risk	Extremely low risk of side effects.	Potential for digestive upset, higher risk of kidney stones, especially for at-risk individuals.
Long-Term Safety	Very safe for long-term daily consumption.	Generally considered safe for most healthy adults, but long-term effects on nutrient balance and side effect risks require monitoring.
Cost	Negligible, as part of a regular diet.	Can be a significant ongoing cost.

The Role of Food in Your Vitamin C Intake

Reliance on supplements, especially high doses, can obscure the importance of whole-food nutrition. Fruits and vegetables provide a rich array of vitamins, minerals, fiber, and other phytonutrients that work synergistically to promote health. Some excellent dietary sources of vitamin C include:

Citrus Fruits: Oranges, lemons, and grapefruits.
Berries: Strawberries and kiwi fruit.
Vegetables: Bell peppers, broccoli, spinach, and kale.

Including these foods in your daily diet is the most natural and effective way to maintain healthy vitamin C levels. Taking a supplement is just that—a supplement to, not a replacement for, a healthy diet.

What if you're sick? The truth about vitamin C and colds

Despite its reputation, megadoses of vitamin C are not a magic bullet for preventing or curing the common cold. The vast majority of studies show that regular, high-dose vitamin C has minimal effect on preventing colds in the general population. However, some research indicates it might slightly reduce the duration and severity of a cold if taken consistently. This suggests that an emergency 1000mg dose at the first sign of a cold may not be as effective as believed. The immune-boosting effect is more complex and involves a multitude of nutrients and lifestyle factors, not just high-dose vitamin C.

Conclusion: Making an Informed Decision

For most healthy individuals, taking 1000mg of vitamin C daily is unlikely to be harmful, as excess is excreted. However, it's a megadose that may offer minimal benefits beyond what a nutritious, vitamin C-rich diet provides. The potential risks, such as digestive issues and increased kidney stone formation (especially in vulnerable individuals), are key considerations. For optimal health, focus on getting your vitamins from whole foods first. If you are considering long-term high-dose supplementation, it is always best to consult with a healthcare provider to ensure it is appropriate for your specific health profile and needs.

For more in-depth information, you can consult the NIH Office of Dietary Supplements' fact sheet on Vitamin C.

Frequently Asked Questions

For most healthy adults, 1000mg is below the Tolerable Upper Intake Level (UL) of 2,000mg and is generally considered safe. However, it is a megadose far exceeding the 75-90mg Recommended Dietary Allowance (RDA), and for many, the extra amount provides no additional benefit and may cause side effects.

Long-term daily use of 1000mg is safe for most healthy people. However, individuals with a history of kidney stones or other specific health conditions should consult a doctor, as there may be increased risks over time.

The most common side effects from high doses of vitamin C are related to digestive issues and can include diarrhea, stomach cramps, nausea, and heartburn. These are generally mild and result from unabsorbed vitamin C in the gut.

While vitamin C is vital for immune function, megadoses do not significantly boost the immune system or prevent colds in the general population. Some studies suggest it can slightly shorten the duration of a cold, but this requires consistent daily intake, not just taking it when you feel sick.

It is always best to obtain nutrients from food first. Your body absorbs vitamin C more efficiently from a balanced diet, and food sources provide other beneficial compounds. Supplements should be used to complement a healthy diet, not replace it.

For most people, a 1000mg dose does not cause kidney stones. However, individuals with a history of kidney stones have an increased risk, as excess vitamin C is converted to oxalate, which can form stones.

There is a rare, unproven concern about 'rebound scurvy' if high-dose vitamin C intake is stopped abruptly, but this is unlikely to happen from a 1000mg dose. For most people, there are no significant side effects from stopping supplementation.

No. People with chronic kidney disease should avoid taking high doses of vitamin C. The increased oxalate excretion resulting from high intake could lead to complications and potentially kidney failure.

Vitamin C is essential for collagen production, which supports healthy skin. While higher doses might theoretically help, the effect of 1000mg supplements on skin health beyond what a standard diet provides has not been definitively proven.

Adults should aim for the Recommended Dietary Allowance (RDA) of 75-90mg per day through a diet rich in fruits and vegetables. This is sufficient to meet the body's essential needs.