The Health Benefits of Vitamin C

Vitamin C is a water-soluble vitamin necessary for tissue growth, development, and repair. An antioxidant, vitamin C is used to strengthen immunity, improve cardiovascular health, and boost iron absorption. 

Your body cannot produce vitamin C and must get it through diet. Vitamin C–rich foods include citrus fruits, berries, broccoli, cabbage, peppers, potatoes, and tomatoes. Vitamin C supplements are available as capsules, chewable tablets, and powder that is added to water.

This article discusses vitamin C benefits, uses, and sources. It also explains the symptoms of vitamin C deficiency, possible side effects, precautions, and interactions.

What Is Vitamin C?

Vitamin C, or L-ascorbic acid, is an essential nutrient. That means your body doesn't make it, so you have to get it through diet or supplements. Vitamin C is in many foods, such as oranges, red and green peppers, and kiwi.

Research has confirmed some general health benefits of vitamin C. When it comes to using it as a treatment or preventive measure for specific conditions, though, many of the studies have been inconclusive or found no benefit.

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.

Antioxidant Activity

Vitamin C is an antioxidant, meaning it's one of many natural substances that may help treat, slow, or prevent some health problems. They do 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 (OS). Research has linked many chronic diseases to OS.

Preventing or reducing OS may help stave off these and other health problems by:

• Boosting your immune system
• Lowering inflammation
• Keeping your cells healthy

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 OS, 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.

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 the buildup of plaque made 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:

• Ischemia (impaired blood flow)
• Hypertension (high blood pressure)
• Cardiomyopathy (conditions of the heart muscle)
• Cardiac hypertrophy (enlargement and thickening of the heart muscle)
• Congestive heart failure (impaired pumping ability)

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.

Cancer Treatment and Prevention

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.

When it comes to cancer, it's become clear that antioxidants aren't all good or all bad. Studies have also shown that antioxidants 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.

Gout

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 in humans need to be done to say for sure that it's a safe and effective treatment or preventive measure.

Iron-Deficiency Anemia

In 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.

Immunity and 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 vitamin E, topically)
  

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.

The Common Cold

Traditional wisdom about 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:

• Don't do anything to prevent the common cold in most people
• May reduce the severity or length 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. For example, one systematic review including eight studies found vitamin C may only have a minimal or no effect on how long your cold lasts. However, a separate meta-analysis found it may shorten the duration.

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

Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is an eye disorder that can, over time, cause blindness. Research has been inconclusive on whether vitamin C and other antioxidants can prevent AMD. 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. Research from 2017 concludes that vitamin C "probably" doesn't prevent or delay AMD and that vitamin E and beta carotene do not. 

Neurodegenerative and Mental Health Disorders

Vitamin C's antioxidant activity may play a role in brain heath.

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

• Alzheimer's disease
• Parkinson's disease
• Multiple sclerosis
• Amyotrophic lateral sclerosis (ALS)
• Huntington's disease
  

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

• Depression
• Anxiety
• Schizophrenia

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 to go away.

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:

• Fatigue
• Gingivitis (gum disease)
• Petechiae (small red spots on the skin)
• Poor wound healing

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:

• Heartburn
• Nausea
• Headaches
• Stomach cramps
• Diarrhea
• Kidney stones

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 any of the following apply to you:

• 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:

Age	Daily Vitamin C Dose*
0 to 6 months	40 mg
7 to 12 months	50 mg
1 to 3 years	15 mg
4 and 8 years	25 mg
9 to 13 years	45 mg
14 to 18 years (females)	65 mg
14 to 18 years (males)	75 mg
14 to 18 years (during pregnancy)	80 mg
14 to 18 years (breastfeeding)	115 mg
19 years and over (females)	75 mg
19 years and over (males)	90 mg
19 years and over (during pregnancy)	85 mg
19 years and over (breastfeeding)	120 mg

Two important caveats to these recommendations are:

• If you smoke, take an additional 35 milligrams per day.
• If you've been diagnosed with a vitamin C deficiency, you'll need between 100 to 200 milligrams per day until a blood test shows normal levels.

Taking high doses may be appropriate for some people, but it usually provides no extra benefit. Your body controls how much vitamin C it absorbs.

That means it'll take what it needs from food and supplements, and anything beyond that comes out in your urine. Taking 1,000 milligrams a day or more actually drops your absorption rate by about 50%.

Upper Limits

The tolerable upper intake level (TUL) is the highest amount you can safely take. Doses beyond that are more likely to cause side effects.

For vitamin C, the daily TUL is different for different groups:

Adults: 2,000 milligrams

Children:

• 1 to 3 years: Less than 400 milligrams
• 4 to 8 years: Less than 650 milligrams
• 9 to 13 years: Less than 1,200 milligrams
• 14 to 18 years: Less than 1,800 milligrams

The TUL during pregnancy is the same as those for your age group.

What Happens If I Take Too Much Vitamin C?

Excessive amounts of vitamin C (above TUL) can result in:

• Nausea
• Vomiting
• Diarrhea
• Stomach cramps

If you're healthy, taking recommended levels of vitamin C supplements generally doesn't pose risks.

Interactions

If you take estrogen or estrogen-based contraceptives, vitamin C may increase the risk of hormonal side effects. This is because vitamin C may slow the rate at which estrogen leaves your body.

Vitamin C can also increase the absorption of certain drugs, such as:

• Aluminum from antacids: It's recommended to take vitamin C two hours before and four hours after taking an antacid.
• Levothyroxine, a thyroid hormone treatment

Vitamin C supplementation can make some medications less effective including:

• The antipsychotic drug fluphenazine
• Certain HIV medications, such as indinavir
• Certain chemotherapy drugs

This is not a complete list of interactions that may occur with vitamin C. Let your healthcare provider and pharmacist know about everything you're taking, including prescription and over-the-counter drugs, vitamins, and herbal supplements.

Talk to your healthcare provider before starting vitamin C supplementation or adjusting your intake.

How to Store Vitamin C

Store vitamin C supplements in a closed container, away from exposure to light.

Sources of Vitamin C & What to Look For

Vitamin C is readily available in your diet and most people can get the required amounts from food.

Multiple vitamin C supplement formulations are readily available. You can buy them from most stores and websites that sell nutritional supplements.

Food Sources of Vitamin C

It is always best to get your nutrients from food rather than supplements.

Fruits and vegetables, especially citrus fruits, are good sources. Foods naturally rich in vitamin C include:

• Raw red bell peppers: 95 milligrams per 1/2-cup serving
• Orange juice: 93 milligrams per 3/4-cup serving
• Orange: 70 milligrams per one medium fruit
• Kiwi: 64 milligrams per one medium fruit
• Raw green peppers: 60 milligrams per 1/2-cup serving
• Cooked broccoli: 51 milligrams per 1/2-cup serving
• Strawberries: 49 milligrams per 1/2-cup serving
• Cooked Brussels sprouts: 48 milligrams per 1/2-cup serving
• Tomato juice: 33 milligrams per 3/4-cup serving
• Cantaloupe: 29 milligrams per 1/2-cup serving

If you don't get enough vitamin C from what you eat, a supplement can help get you to the right levels.

Vitamin C Supplements

Vitamin C supplements are available as a single nutrient supplement or combination supplement. You can find them in many forms, such as:

• Tablets
• Capsules
• Chewable tablets
• Gummies
• Dissolving powders and tablets

You may also see different types of vitamin C, including:

• L-ascorbic acid: Typically derived from corn
• Combination supplements: Common ingredients are sodium or calcium
• Citrus bioflavonoids: Compounds from fruits such as oranges, grapefruits, and tangerines
• Rose hips: A type of wild plant sometimes used in medicinal compounds
• Acerola powder: The fruit acerola has a high ascorbic acid content
• Camu camu: A type of berry that grows on shrubs in the Amazon rainforests

No one form is more effective than another. Remember to look at the dosages and avoid exceeding the TUL.

Also, pay attention to units of measure. The RDA for vitamin C is in milligrams (mg), but vitamin C labels may list grams (g) or micrograms (mcg).

• 1 milligram (mg) = 1,000 micrograms (mcg)
• 1 gram (g) = 1,000 milligrams

Dietary supplements aren't regulated by the FDA. When possible, choose a supplement that's been tested by a trusted third party, such as:

• USP
• ConsumerLabs
• NSF

This ensures their purity and that the contents match the label. It doesn't guarantee effectiveness.

Summary

Vitamin C supplements have been marketed for many conditions. It's the best treatment for vitamin C deficiency.

As an antioxidant and anti-inflammatory, vitamin C has been studied for its uses in heart disease prevention, gout, immunity, and more.

It is best to get vitamin C from your food. If you don't, a supplement can help you meet your goals. Talk to your healthcare provider before taking supplements.

The right dosage depends on several factors, including age and medical conditions. In addition, vitamin C can interact with certain medications and cause side effects at high levels, so it is important to discuss with your healthcare provider whether supplementation is appropriate for you.