Vitamin C: what is it, benefits, dosage

Human beings need vitamin C to live. Go without it for a month or two, and the walls of your blood vessels will gradually break down. This condition—also known as scurvy—eventually leads to internal bleeding and sometimes death (Wijkmans, 2016). 

That’s the most extreme case. But even minor vitamin C shortfalls may interfere with proper health and functioning. Also, some people—for example, those who smoke—may require more vitamin C than others (Carr, 2021). 

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Vitamin C, which is also called ascorbic acid, is an essential nutrient. That means your body needs it but can’t make it itself, so you have to get it from your diet or from supplements. It’s also a water-soluble vitamin, which means it breaks down in water and the body can put it to use immediately. Water-soluble vitamins are usually not stored in the body and need to be replenished regularly in our diet (Carr, 2017). 

In addition to it being an essential nutrient, vitamin C has antioxidant properties. That means it can prevent or counteract cell damage or dysfunction caused by free radicals, oxidative stress, and other toxins (Abdullah, 2021). 

It also plays a critical role in many biological functions. It helps regulate the activity of your immune system, and can prevent or reduce harmful forms of inflammation (Abdullah, 2021). It also helps your body make collagen, which is the main ingredient in your connective tissues (Wijkmans, 2016). 

Apart from keeping you alive and in good working order, the beneficial effects of vitamin C may also help protect you from various ailments or illnesses. Here are a few reasons why it’s a good idea to consume vitamin C regularly.

Heart and blood benefits

Studies link proper vitamin C intake to healthier systolic and diastolic blood pressure scores. Some research, albeit preliminary, has also found that a high intake of vitamin C may lower your risk for heart disease (Carr, 2021).  

Muscle and performance benefits

Research shows that vitamin C may prevent age-related muscle breakdown. It does this in part by protecting muscle fibers from damage and by supporting the cell structures that make up muscle. It may also support optimal physical performance (Takisawa, 2019).

Immune health

Vitamin C plays a critical role in the healthy operation of your immune system. Without it, immune cells called cytokines don’t work properly. Your levels of inflammation can also become imbalanced. 

These may be just two of many immunity-related problems that can crop up if you don’t get enough vitamin C. Some evidence links taking vitamin C supplements to shorter durations of the common cold, but there’s not enough data to say that vitamin C can prevent the common cold or other respiratory infections (NIH, 2021; Carr, 2017). 

One big study looking at 11,306 people showed that supplementing with vitamin C did not lower the incidence of colds, but it did shorten the duration of symptoms by 8% in adults and 14% in children (Hemilä, 2013).

Disease prevention

Some evidence—albeit limited—shows that vitamin C may prevent several medical conditions. These include stroke, diabetes, cardiovascular disease, and some forms of cancer, mainly by curbing the damaging effects of free radicals. But more research is needed to establish these benefits (Abdullah, 2021). 

Nutrient absorption

Vitamin C helps your body take in or store other helpful nutrients. For example, vitamin C helps improve iron absorption (Abdullah, 2021). 

Your body doesn’t do a good job of storing or holding onto vitamin C. Because of that, you need to take it in regularly (Carr, 2017). A true vitamin C deficiency is pretty rare. Around 90-95% of adults get enough through diet alone and aren’t at risk for a vitamin C deficiency (Pfeiffer, 2013). 

While extreme forms of vitamin C deficiency—a.k.a., scurvy—are uncommon in developed countries like the U.S., milder vitamin C deficiencies are not unusual. Roughly 7% of Americans may be deficient (Schleicher, 2009). 

The risk is most significant among certain groups. These include (Maxfield, 2021): 

• People who smoke

• People with an alcohol use disorder

• Older adults who eat a restricted diet and those who don’t have access to fruits and vegetables

• People with eating disorders

• People with GI disorders or type-1 diabetes

The symptoms of a vitamin C deficiency tend to emerge after 8–12 weeks of low intake levels. These symptoms are diverse and include poor wound healing, leg pain, skin or nail problems, swollen or bleeding gums, loose teeth, bruising, and red or purple spots on the skin (petechiae) (Maxfield, 2021; Marik, 2019):

Diagnosis of a vitamin C deficiency usually starts with a physical exam to check for the above symptoms. If your medical provider thinks you may have a vitamin C deficiency, blood tests can confirm this (Maxfield, 2021).

Treatment depends on the underlying cause of your deficiency. In most cases, you’ll need to take some kind of vitamin C supplement—something containing anywhere from 100 to 2,000 mg (Maxfield, 2021). 

You can get vitamin C from two sources: foods and dietary supplements. 

Foods

While many different foods contain a little vitamin C, fruits and vegetables are the best sources (Abdullah, 2021).  In particular, the following foods have a high vitamin C content (Abdullah, 2021; Wijkmans, 2016):

• Citrus fruits, such as oranges, grapefruits, lemons, and limes

• Fruit juices, such as orange juice and grapefruit juice

• Berries

• Kiwifruit

• Tomatoes

• Potatoes

• Green leafy vegetables

• Broccoli

• Sweet peppers, such as red pepper

• Cantaloupe

For example, a single orange contains about 80 mg of vitamin C. Meanwhile, a cup of chopped broccoli has about 70 mg (USDA, n.d.). 

Supplements

There are countless vitamin C supplements for sale, including most multivitamins. Sometimes, one serving of these high-dose supplements has 1,000 mg of vitamin C. 

The general recommendation is that people over the age of 19 should not consume more than 2,000 mg of vitamin C in a day. This is called the “tolerable upper limit” intake —the maximum amount of a vitamin or mineral people can consume without the likelihood of experiencing adverse health effects (NIH, 2021). 

Research suggests that vitamin C is safe for most people—even in high doses (Carr, 2021). But there are reasons to be careful with supplement sources. 

For example, high doses of vitamin C supplements may be risky for people with blood disorders. These supplements can also raise blood sugar levels (glucose) and may be problematic for people with diabetes (Abdullah, 2021). 

Before taking a vitamin C supplement, you may want to talk with your medical provider to double-check that it's safe. 

That may seem like a straightforward question, but there’s more than one correct answer. For one thing, there appears to be a big difference in the amount of vitamin C your body needs to avoid deficiency problems and how much you need to take to optimize health (Carr, 2021). 

Also, some groups may require more vitamin C than others. These include (Abdullah, 2021):

• Older adults

• Those with alcohol use disorders or anorexia

• Those on specialized or restricted diets (such as very low or no-carb diets)

• Those with kidney problems

• Those who smoke

As a result, recommended dietary allowances (RDAs) for the daily intake of vitamin C vary a lot from country to country. For example, France recommends that adult men and women aim for 110 mg/day, while the recommendation in the U.S. is 90 mg/day for men and 75 mg/day for women (Carr, 2021). 

For other groups in the U.S., the National Institutes of Health (NIH) offers the following RDAs based on age (NIH, 2021): 

• Infants 0 to 6 months: 40 mg

• Infants 7-12 months: 50 mg

• Kids 1 to 3: 15 mg

• Kids 4 to 8: 25 mg

• Kids 9 to 13: 45 mg

• Kids 14 to 18: 75 mg for men, and 65 for women

• Women who are pregnant: 80 to 85 mg

• Women who are breastfeeding or lactating: 115 to 120 mg

While those are the recommendations, some research suggests that aiming for 200 mg/day may optimize health without leading to any health risks (Carr, 2021). 

Unless you have a diagnosed deficiency, most experts recommend that you try to get vitamin C from food sources such as the ones listed above (Abdullah, 2021). Eating five daily servings of fruits and vegetables should help you hit 200 mg (Carr, 2021). 

If, for some reason, you can’t hit your daily vitamin C targets with foods alone, supplements can help fill shortfalls. But again, talk to your healthcare provider first (Abdullah, 2021). 

Vitamin C does all sorts of important work in your body. Consider it another reason to eat plenty of healthy fruits and vegetables. If you’re not—or you can’t—you may want to talk with a healthcare provider about your risks for a deficiency. 

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Current version

November 15, 2021

Written by

Health Guide Team

Fact checked by

Felix Gussone, MD

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About the medical reviewer

Felix Gussone, MD, Ro

Felix Gussone is a physician, health journalist and a Manager, Medical Content & Education at Ro.