Benefits, Side Effects, Dosage, Interactions

Vitamin C is touted for many potential health benefits, including boosting immunity, improving heart health, and bolstering iron absorption. It’s essential for tissue growth, development, and repair. As an antioxidant, it may help protect cells from free radicals—unstable molecules that damage cells. However, its benefits for specific diseases and conditions remain unproven.

What Is Vitamin C?

Vitamin C, or L-ascorbic acid, is an essential nutrient. The body can’t manufacture it, relying instead on vitamin C–rich foods such as berries, broccoli, cabbage, citrus fruits, kiwi, oranges, peppers, and tomatoes. In addition, vitamin C supplements are available as capsules, chewable tablets, and powder.

Research shows vitamin C has many general health benefits. However, the science is inconclusive on using vitamin C to treat or prevent specific health conditions.

Vitamin C Benefits and Uses

Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian, pharmacist, or healthcare provider. No supplement is intended to treat, cure, or prevent any disease.

Vitamin C has been marketed for use to treat and/or prevent many conditions, from the common cold and COVID-19 to arthritis and Alzheimer’s disease. Even so, there’s scant evidence to support most claims about vitamin C.

What researchers have learned is that vitamin C appears to play a lot of important roles in your body. The most beneficial aspect may be its antioxidant activity.

May Lower Risk of Chronic Illnesses

Vitamin C is an antioxidant, meaning it’s one of many natural substances that may help treat, slow, or prevent some health problems. It does this by neutralizing free radicals, which are unstable molecules that can damage cells and cause disease.

When you have a lot of free radicals in your system, it can cause a condition called oxidative stress. Research has linked many chronic diseases to oxidative stress, including heart disease, rheumatoid arthritis, chronic obstructive pulmonary disease (COPD), and kidney disease.

Preventing or reducing oxidative stress may help stave off health problems by:

However, research into using antioxidants to treat or prevent specific conditions has been a mixed bag.

Free radicals come in many types; some are harder for antioxidants to scavenge. Their location in your body can also make a difference, as certain environments (e.g., inside a cell versus in fluids outside the cell) can make the antioxidant activity more or less successful.

Moreover, researchers say it’s important to be “realistic about where, when and to what extent oxidative stress is part of a disease.” So, as they learn more about the disease processes and the role of oxidative stress, researchers may find roles for antioxidants like vitamin C.

In the meantime, while they’re generally considered good for your health, don’t expect vitamin C or any other antioxidants to take the place of other treatments.

May Lower Heart Disease Risk

Oxidative stress is believed to play a role in the development of some cardiovascular diseases (“cardio” means heart, “vascular” refers to blood vessels).

A major reason for this is that oxidative stress can trigger atherosclerosis, which is the thickening or hardening of arteries due to plaque buildup from cholesterol, fat, and other substances. This can lead to coronary artery disease.

Studies have also suggested that oxidative stress may play some role in:

Even so, research into vitamin C for treating and preventing heart disease has mostly found no effect.

One promising bit of information came out in a 2020 study. It showed that vitamin C supplements helped lower blood pressure in people with hypertension. Hypertension, especially when combined with atherosclerosis, is a risk factor for heart disease.

May Help Reduce Risk of Certain Cancers

A lot of research has investigated the role of antioxidants, including vitamin C, in cancer care and prevention. However, the results have yielded inconsistent results.

Most studies have found that vitamin C supplementation, either on its own or in combination with other supplements, cannot prevent or treat cancer.

Some studies have shown that when used in supportive care, high-dose intravenous (IV) vitamin C can improve quality of life and reduce the side effects of standard cancer treatments. However, studies have also shown that antioxidants can have a downside. They may:

• Help cancerous or pre-cancerous cells survive
• Possibly make some cancer treatments less effective

Some healthcare providers recommend eating more antioxidant-containing fruits and vegetables, as people with diets rich in vitamin C may have a lower risk of getting certain types of cancer. However, it’s important to remember that no one food will prevent cancer.

Moreover, vitamin C supplements themselves do not appear to prevent cancer. Eating a well-balanced diet in general, including antioxidants, is beneficial for your overall health.

Future studies are needed to establish the role of antioxidants like vitamin C in cancer. Talk to your oncologist before starting any supplements during cancer treatment.

Can Prevent Gout Attacks

Gout is a common and extremely painful type of arthritis that mainly affects the big toes. It’s caused by excess uric acid (a waste product) in the blood, which causes crystals to form in the joints. The crystals then cause inflammation, which leads to painful attacks.

Several studies have shown that vitamin C can prevent gout by lowering levels of uric acid in the blood. This may, at least in part, be due to its antioxidant activity. Uric acid levels appear to be higher in people with significant oxidative stress.

However, a 2021 review of studies concluded that, while results have been promising, more high-quality studies on humans need to be done to say for sure that it’s a safe and effective treatment or preventive measure.

Prevents Iron-Deficiency Anemia

With anemia, your blood doesn’t contain enough red blood cells, which carry oxygen from your lungs to your body’s tissues. The most common type of anemia involves a deficiency of iron, which your body needs to make red blood cells.

Vitamin C is known to help your body absorb some nutrients. Among healthcare providers, that led to a long-standing practice of recommending vitamin C supplements with iron supplements for treating anemia.

A 2019 article found that vitamin C increased iron absorption by 67%. A 2020 study casts doubt on that, though. It found that iron supplements alone improved anemia just as much as iron plus vitamin C.

The different results may be related to what kind of iron people took. Nonheme iron from plant sources is better absorbed with vitamin C. Heme iron, the form found in meat, is better absorbed in general because it has higher bioavailability than nonheme iron. More research is needed to sort this out.

Boosts Immunity and Speeds Healing

Vitamin C’s best-known use is for boosting the immune system. It does this by:

• Helping your body make several types of specialized immune cells that guard against infection
• Improving the function of those immune cells
• Protecting them from damage by free radicals

Studies show vitamin C’s effect on the immune system may help with certain infections, such as:

• COVID-19
• Pneumonia
• Sepsis (an extreme, life-threatening response to infection)
• Other respiratory infections

Vitamin C is also sometimes used orally (by mouth) or topically (applied to the skin) for skin healing. According to research, vitamin C use may:

• Reduce deaths from severe burns (in high oral or IV doses soon after admission to a hospital)
• Promote wound healing (orally or topically)
• Reduce skin inflammation in conditions such as psoriasis and atopic dermatitis (orally or topically)
• Protect skin against damage from the sun (orally or along with topical vitamin E)

These abilities are believed to be largely due to vitamin C’s antioxidant activity along with its ability to promote collagen production in the skin.

This is likely better achieved with nutritional intake (including supplements) rather than topically because collagen is present in deeper layers of skin and can’t penetrate the outer layers to get there.

Fights the Common Cold

Traditional wisdom about taking vitamin C for the common cold may not be as wise as you think. Research has provided mixed evidence about vitamin C for treating or preventing these respiratory infections.

Several studies, including a large systematic review of the evidence, suggest vitamin C supplements:

• May shorten the duration of the common cold
• May reduce the severity of cold symptoms
• May reduce the likelihood of colds in people in extreme environments (e.g., soldiers, endurance athletes)

Even these points aren’t firmly conclusive, though, and some studies have found vitamin C may only have a minimal or no effect on how long your cold lasts.

More research needs to be done before researchers can draw any firm conclusions.

Slows Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is an eye disorder that can, over time, cause blindness. Research on whether vitamin C and other antioxidants can prevent AMD has been inconclusive. But some research suggests it may slow it down.

The Age-Related Eye Disease Study (AREDS), a large clinical trial, included almost 3,600 older adults with AMD. The participants were divided into four groups and given different treatments:

• Group 1: Antioxidant supplements: vitamin C, beta carotene, vitamin E
• Group 2: Zinc, copper
• Group 3: Antioxidants plus zinc
• Group 4: Placebo

After six years, the participants who got supplements had less AMD progression. However, researchers can’t be sure that vitamin C itself made a difference.

This is an older study, though, and since then, a number of other studies have failed to show that vitamin C alone is helpful against AMD. However, a 2023 Cochrane review found vitamin C, taken alone with vitamin E, beta‐carotene, and zinc, probably slows down progression to late AMD.

Protects Brain Health

Vitamin C’s antioxidant activity may play a role in brain health.

Research suggests regular dietary intake plus supplements may protect you from neurodegeneration related to aging and diseases such as:

Vitamin C may even help treat or lower your risk of mental health disorders, including:

Studies suggest vitamin C deficiency may contribute to the development of these mental and neurodegenerative conditions and that supplementation may help alleviate symptoms. However, this work is preliminary, and more research is needed.

Vitamin C Deficiency

Vitamin C deficiency is rare in developed countries. In the United States, only about 8.4% of the population is believed to be vitamin C deficient.

You’d have to get less than 10 milligrams (mg) per day from food for about a month to feel the effects of a vitamin C deficiency. In severe cases, this can lead to scurvy (which is rare in the U.S.).

Symptoms of scurvy include:

• Bruising
• Bleeding gums
• Weakness
• Fatigue
• Rash

Vitamin C deficiency is treated with vitamin C supplements. Some symptoms improve within the first 24 hours of treatment. Others may take a few weeks or months to resolve.

What Causes a Vitamin C Deficiency?

A deficiency occurs either from insufficient nutrient intake in the diet or increased losses due to poor absorption.

People who don’t consume various foods, mainly fruits and vegetables, are at greater risk of vitamin C deficiency. Smokers have a higher requirement for vitamin C, so smoking may also be a risk factor.

Additionally, people with malabsorption disorders may become deficient because they can’t absorb enough vitamin C.

How Do I Know if I Have a Vitamin C Deficiency?

Symptoms of a vitamin C deficiency include:

If you have these symptoms and know your vitamin C intake is low, or if you rarely eat fruits and vegetables, talk with your healthcare provider about whether supplements are right for you.

What Are the Side Effects of Vitamin C?

Vitamin C is generally considered safe, but high doses can cause side effects. These may include:

Higher doses are more likely to lead to side effects. Doses over 2,000 milligrams a day may increase the risk of diarrhea and kidney stones. If you have a history of kidney stones, taking more than 1,000 milligrams a day may increase your chances of having more.

Precautions

Vitamin C supplements are not right for everyone. Talk to your healthcare provider first if you are experiencing any of the following:

• Undergoing cancer treatment: Vitamin C supplements can interact with some cancer therapies.
• Chronic kidney disease: Vitamin C can increase oxalate formation and lead to kidney failure.
• G6PD: Large amounts of vitamin C (administered intravenously) have caused hemolysis (the breakdown of red blood cells) in people with a metabolic disorder called glucose-6-phosphate dehydrogenase (or G6PD). However, this is uncommon.
• Iron overload: Vitamin C supplementation can exacerbate symptoms since it has a role in iron absorption.

Dosage: How Much Vitamin C Should I Get?

Always speak with a healthcare provider before taking a supplement to ensure that the supplement and dosage are appropriate for your individual needs.

For most healthy people, it is easy to get adequate amounts of vitamin C through food. You can meet your recommended dietary allowance (RDA) for vitamin C each day by eating just one of the following:

• Kiwi fruit
• Red bell pepper
• Cup of tomato juice
• Orange
• Cup of strawberries

The RDA for vitamin C is as follows: