How Many Grams of Ascorbic Acid Per Day?

December 10, 2025 •

4 min read

The human body cannot produce its own vitamin C, also known as ascorbic acid, and must obtain it from diet. Given this, understanding how many grams of ascorbic acid per day are necessary for optimal health is crucial for most adults.

Quick Summary

The recommended daily intake of vitamin C varies by age and gender, but is typically in milligrams, not grams. Most adults should aim for 75-90 mg daily, with a tolerable upper limit of 2,000 mg to avoid side effects like diarrhea and stomach cramps. Higher doses are usually unnecessary.

Key Points

RDA is in milligrams: The recommended daily allowance of ascorbic acid for adults is 75-90 mg, which is far less than a gram.
Upper intake is 2 grams: The tolerable upper intake level for adults is 2,000 mg (2 grams) to avoid adverse effects.
Excess causes stomach issues: Consuming more than 2,000 mg daily can cause gastrointestinal problems like diarrhea, nausea, and cramps.
High doses can increase kidney stone risk: Individuals prone to kidney stones should be cautious with high vitamin C supplementation, as it can increase oxalate excretion.
Food is the best source: Getting vitamin C from fruits and vegetables is generally preferable as it provides other nutrients and fiber.
Smokers need more: Individuals who smoke require an additional 35 mg of vitamin C per day.
Mega-dosing is not better: Large doses of vitamin C are not proven to offer additional health benefits beyond a certain point and can lead to adverse side effects.

Ascorbic Acid: A Milligram-Based Daily Requirement

For most people, the daily requirement for vitamin C, or ascorbic acid, is measured in milligrams (mg), not grams (g). The term 'gram' refers to a much larger quantity (1,000 milligrams) than what is typically needed for daily nutritional support. Understanding the Recommended Dietary Allowance (RDA) and Tolerable Upper Intake Level (UL) is key to a healthy intake.

Recommended Daily Allowances (RDAs)

The National Institutes of Health (NIH) and other health authorities provide specific RDAs for vitamin C based on age, gender, and life stage. These are the amounts considered sufficient to meet the nutritional needs of nearly all healthy individuals. Smokers require an additional 35 mg per day due to increased oxidative stress.

Adult Men: 90 mg per day
Adult Women: 75 mg per day
Pregnant Women: 85 mg per day
Breastfeeding Women: 120 mg per day

Most people can meet these needs through a balanced diet rich in fruits and vegetables, such as oranges, broccoli, and red peppers. For example, a single medium orange can provide a significant portion of the daily requirement.

Tolerable Upper Intake Levels (ULs)

The UL is the maximum daily intake that is unlikely to cause harmful effects. For adults, the UL for vitamin C is 2,000 mg, or 2 grams, per day. Doses exceeding this can lead to gastrointestinal distress, such as diarrhea, nausea, and stomach cramps. The body is not efficient at absorbing very high doses, with absorption rates dropping significantly at intakes above 1 gram.

The Role of Ascorbic Acid in the Body

Ascorbic acid is a powerful antioxidant that plays numerous roles in the body. It is vital for the growth, development, and repair of all body tissues.

Collagen Formation: It is essential for producing collagen, a key protein for maintaining skin, tendons, ligaments, and blood vessels.
Iron Absorption: Vitamin C enhances the absorption of non-heme iron from plant-based foods, which is particularly beneficial for those with low iron stores.
Immune System Support: It helps stimulate white blood cell activity, supporting the body's immune response.
Wound Healing: Ascorbic acid is necessary for the healing of wounds and the formation of scar tissue.

Can Megadosing with Ascorbic Acid Be Harmful?

Because vitamin C is water-soluble, excess amounts are typically excreted in the urine, making serious toxicity rare. However, this does not mean that megadosing is harmless. Consuming large doses of supplements consistently above the UL can lead to unpleasant and potentially serious health issues.

Gastrointestinal Issues: The most common side effects of high intake are digestive problems like diarrhea, nausea, and stomach cramps, caused by unabsorbed vitamin C drawing water into the gastrointestinal tract.
Kidney Stones: In individuals predisposed to kidney stones, particularly those with a history of them, high doses (above 1,000 mg/day) may increase the risk of developing more stones.
Interference with Tests: Very high doses can interfere with certain lab tests, such as blood sugar readings, which can be particularly problematic for diabetic individuals.
Iron Overload: For those with hereditary hemochromatosis, a condition causing the body to store too much iron, excessive vitamin C can exacerbate iron accumulation and lead to tissue damage.

Natural Sources vs. Supplements

While supplements are widely available, getting vitamin C from whole foods is generally recommended. Food sources offer a broader spectrum of nutrients and fiber, enhancing overall health.


Comparison of Dietary and Supplemental Ascorbic Acid	Feature	Dietary Ascorbic Acid	Supplemental Ascorbic Acid
Source	Fruits, vegetables (e.g., oranges, peppers, broccoli)	Tablets, capsules, powders
Nutrient Synergy	Comes with other vitamins, minerals, and fiber	Usually isolated nutrient; can be combined in multivitamins
Absorption	Highly efficient, especially at typical dietary levels (30-180 mg)	Absorption rates decrease with high doses (above 1 g)
Toxicity Risk	Extremely low risk from food sources alone	Higher risk of gastrointestinal issues and other side effects at high doses
Overall Benefit	Generally considered superior for overall nutrition	Convenient for filling dietary gaps or addressing deficiencies

For most healthy individuals, meeting the recommended milligrams of ascorbic acid through a balanced diet is simple and effective. If supplementation is considered, staying within the 2,000 mg UL is crucial to prevent adverse effects. Always consult a healthcare provider for personalized advice, especially for high-dose regimens or if you have pre-existing health conditions.

Conclusion: Focus on Milligrams, Not Grams

To answer the question, how many grams of ascorbic acid per day is not the correct framing for most people. The appropriate intake is measured in milligrams, with recommended daily amounts for adults ranging from 75 to 90 mg. While the body can tolerate higher intakes up to 2 grams (2,000 mg), going beyond this limit significantly increases the risk of side effects like gastrointestinal discomfort and potential kidney stone formation. For optimal health, focus on incorporating vitamin C-rich foods into your daily diet rather than relying on high-dose supplements. This approach ensures you receive the benefits of this vital nutrient without the risks associated with megadosing. For more detailed medical guidance, resources like those from the National Institutes of Health are invaluable.

Frequently Asked Questions

A gram is a unit of mass equal to 1,000 milligrams. The body's nutritional need for ascorbic acid is in milligrams (e.g., 75-90 mg per day), while the tolerable upper limit is 2,000 mg, which is 2 grams. High-dose supplements often contain amounts measured in grams.

Yes, for most people, a balanced diet rich in fruits and vegetables is sufficient to meet the daily requirements for vitamin C. Good sources include citrus fruits, bell peppers, strawberries, and broccoli.

The most common first signs are gastrointestinal issues such as diarrhea, nausea, and stomach cramps. These occur because the body cannot absorb very high doses and the unabsorbed vitamin C affects the digestive tract.

Scientific evidence is mixed on this. While some studies suggest regular intake might slightly shorten the duration or severity of a cold, there is no strong evidence that large doses prevent colds in the general population.

Smokers and those exposed to secondhand smoke require an additional 35 mg of vitamin C per day beyond the standard RDA for their age and gender.

Taking more than 2,000 mg (2 grams) per day is not recommended for adults as it may cause unpleasant and potentially harmful side effects. This is the established Tolerable Upper Intake Level.

If you have conditions like chronic kidney disease, a history of kidney stones, or hemochromatosis, you should consult a healthcare provider before taking any vitamin C supplements. High doses may be risky for these conditions.