What Is Vitamin C? A Complete Scientific Guide

Also known as L-ascorbic acid, or sometimes ascorbic acid, vitamin C is a water-soluble vitamin that humans, unlike most other animals, cannot synthesize. That means we must get the recommended levels of vitamin C through diet.

Although you probably see vitamin C everywhere these days — on labels for supplements, cough drops, and even skin-care serums — scientists only discovered its importance at the start of the 20th century, research notes. That’s when they realized vitamin theory, or the idea that the human body needs more than just the macronutrients protein, carbohydrates, and fat to survive. Vitamin C was only the second vitamin, after thiamine, to be isolated and chemically defined.

Today, much is known about the various ways vitamin C is used by our bodies, its potential benefits, and the best sources of this all-important nutrient. This guide provides an overview of what vitamin C is good for, how to know if you’re getting enough, the top sources of it, and more.

What Does Vitamin C Do?

An important antioxidant, vitamin C helps protect cells from damage caused by illness, aging, and environmental factors like ultraviolet (UV) light and pollution, notes the National Institutes of Health (NIH). It’s also required for the body to make collagen, a protein that, among other functions, helps wounds heal. “Vitamin C helps the body repair and regenerate tissues,” says Kate McGowan, RDN, who is based in Hingham, Massachusetts.

But of all its functions, vitamin C is probably best known for its role in immunity. A study found that being deficient in vitamin C can impair immune function and leave you at risk of developing infections. And supplementing with the vitamin may help prevent and treat respiratory and other illnesses, possibly because the vitamin supports the immune cells that identify and dispose of foreign particles in the body, research suggests.

While there is no evidence that taking high levels of vitamin C will prevent the common cold in the general population, it may help with decreasing its duration and severity, but only if you have been taking it consistently before getting sick, the NIH says.

Generally speaking, most healthy adults 19 years and older should get between 65 and 90 milligrams (mg) of vitamin C daily, preferably from food sources, according to the U.S. Department of Agriculture. However, your exact vitamin C needs depend on your age, sex, and whether you’re pregnant or lactating. The NIH recommends the following daily dietary allowances:

• Infants Ages 0 to 6 Months 40 mg
• Infants Ages 7 to 12 Months 50 mg
• Children Ages 1 to 3 Years 15 mg
• Children Ages 4 to 8 Years 25 mg
• Children Ages 9 to 14 years 45 mg
• Teens Ages 14 to 18 Years 65 mg for girls; 75 mg for boys
• Adults 19 Years and Older 75 mg for women; 90 mg for men
• Pregnant Women 80 to 85 mg
• Lactating Women 115 to 120 mg

Some research suggests that other populations, including pregnant and lactating women, athletes, and smokers, may benefit from a higher intake of vitamin C. Smokers, in particular, have a greater risk of vitamin C deficiency — more than three times greater, according to research published in 2020 in Nutrients. That is likely because smoking causes greater vitamin C turnover in the body. Cigarette smoking increases free radicals in the body, which damages cells; antioxidants such as vitamin C counteract the damage but are depleted more quickly in people who smoke.

Likewise, vitamin C supplementation may be helpful to athletes. Specifically, in athletes who experience short periods of extreme physical stress, such as playing in sports competitions, vitamin C might decrease the incidence of the common cold, according to a review published in 2020 in the Frontiers in Immunology.

When considering the administration of vitamin C, foods ought to be your first source. Many fruits and vegetables are good or excellent sources of vitamin C. In some cases, your doctor may recommend supplements if you don’t get enough vitamin C in your diet, and it’s also available in topical form for certain skin-care needs.

Foods

“Most people associate oranges with vitamin C,” says McGowan. “That is great, but I like to switch it up.”

Other excellent sources of vitamin C noted by the NIH include these foods and beverages:

• Red peppers, 95 mg per ½ cup
• Orange juice, 93 mg per ¾ cup
• Oranges, 70 mg per 1 medium fruit
• Kiwi fruit, 64 mg per 1 medium fruit
• Broccoli (cooked), 51 mg per ½ cup
• Broccoli (raw), 39 mg per ½ cup
• Grapefruit juice, 70 mg per ¾ cup
• Grapefruit, 39 mg per ½ medium fruit
• Strawberries, 49 mg per ½ cup
• Brussels sprouts, 48 mg per ½ cup

Other good food sources include potatoes, cauliflower, spinach, and green peas. It’s important to note that vitamin C is heat sensitive, so you’ll get the most from foods when they’re eaten raw (not cooked or heated), per the NIH.

Supplements

Food should be your first source of vitamin C, but in certain cases your healthcare team may recommend supplementation. The FDA doesn’t regulate over-the-counter supplements like vitamin C in the same way they do traditional medications, so it’s important that you speak with a doctor before attempting to self-treat any medical condition.

“If you are eating a balanced diet, most likely you do not need to take a vitamin C supplement,” says McGowan. Vitamin C is water-soluble — meaning the body utilizes it but doesn’t store it, notes Medline Plus.“For most healthy individuals, the body can only hold and use about 200 to 250 mg of vitamin C a day, and any excess is lost through urine,” explains McGowan.

Despite this, you can overconsume vitamin C. Excessive intake is most likely to occur with supplement use, so the NIH says to make sure your total daily intake (food and supplements) falls below the tolerable upper limit, or the maximum daily intake of 2,000 mg recommended for healthy adults. Keep in mind that if you take a multivitamin including vitamin C, you’re also getting the nutrient there, so don’t forget to add that amount to your total supplemental intake.

Skin-Care Products

While vitamin C is the antioxidant most present in human skin, only a small amount of the vitamin you consume makes its way there, even when you supplement orally. That’s why you see bottles of vitamin C serum in the drugstore.

Vitamin C serums can be topically applied to the skin and may provide benefits such as protection against damage caused by UV exposure, as well as age-related skin concerns including collagen damage and wrinkles, research suggests. And while it’s no replacement for sunscreen, a vitamin C serum routinely applied before sun exposure may help prevent premature aging of the skin. It may also help protect against pigmentation issues by interfering with melanin synthesis. You’ll see many varieties of vitamin C serums, including ones with additional ingredients, such as vitamin E or hyaluronic acid.

Vitamin C is perhaps best known for boosting immunity and reducing oxidative stress, but it may also provide other health benefits.

May Help Prevent Chronic Diseases

Vitamin C may play a part in preventing or lowering the risk of several chronic illnesses. According to the NIH, eating high-vitamin C foods, such as fruits and vegetables, may reduce your risk of developing lung, breast, and colon cancers, as well as cardiovascular disease.

In terms of cardiovascular health, a review published in 2020 in Antioxidants suggests that vitamin C has positive effects on vascular health, while also promoting blood flow. Still, the authors note that more research is needed to determine whether vitamin C alone could prevent cardiovascular disease.

Vitamin C is also used in some complementary and integrative cancer therapies. In such cases, high doses may be administered intravenously by a healthcare professional. However, as a review published in 2021 in Antioxidants notes, such methods are still being studied in clinical trials for their safety and efficacy. Researchers also suggest that natural intake of vitamin C from foods could possibly decrease the risk of pancreatic, breast, and pulmonary cancers, but more studies are needed to support definitive links between vitamin C and cancer prevention.

Promotes Eye Health

Vitamin C might even reduce your risk of developing age-related macular degeneration (AMD), as well as cataracts, says the NIH. And, if you already have AMD, the American Academy of Ophthalmology states that 500 mg vitamin C per day combined with vitamin E, zinc, copper, lutein, and zeaxanthin may decrease the risk of dry AMD as well as wet forms.

But more research is needed to determine if and to what degree vitamin C alone is responsible for those effects and whether it’s helpful for preventing and treating any specific health condition. A review published in 2020 in Nutrients found that vitamin C supplements could help delay the development of cataracts due to age and diabetes, but such benefits are primarily seen in individuals who had vitamin C deficiency to begin with.

May Help Regulate Blood Pressure

There is some evidence that taking vitamin C may also help lower blood pressure in people with hypertension. A 2020 meta-analysis of eight randomized controlled trials involving more than 600 participants found that supplementing with vitamin C — the average dose was around 500 mg — led to a significant reduction in blood pressure in participants with high blood pressure, compared with control groups. The effect seemed most pronounced in men ages 60 and older. The study authors noted that further research about the long-term effects of vitamin C supplementation is still needed.

Vitamin C deficiency is considered relatively rare in the United States. There is evidence, however, that many Americans don’t meet their recommended daily allowance of the vitamin. Research published in 2021 in Current Developments in Nutrition reported that between 2003 and 2006, 118 million U.S. adults didn’t get enough vitamin C from their diet alone. And another study published in 2021 in Nutrients found that vitamin C consumption declined by 23 percent between 1999 and 2018, likely as a result of people switching from fruit juice to whole fruit.

Causes and Risk Factors

You don’t need much of this essential vitamin to ward off deficiency: Anything more than 10 mg a day will do, which may be why, these days, vitamin C deficiency is rare, affecting only 6 percent of the American population, per scientific data.

However, certain groups may have an increased risk of vitamin C deficiency. According to the National Center for Biotechnology Information (NCBI), that includes people who smoke, seniors, and individuals who don’t have access to fruits and vegetables. Certain health conditions can also increase your risk, such as type 1 diabetes, inflammatory bowel disease, and alcohol use disorder.

Signs and Symptoms

Scientists discovered vitamin C in part because sailors in the 1700s and 1800s were falling ill and even dying from a lack of the nutrient. The disease, called scurvy, caused weakness, fatigue, poor wound healing, and bleeding gums, and it was caused by low intakes of vitamin C.The cure was ultimately found in citrus fruits, which added vitamin C to a diet that was usually lacking in fresh produce during the sailors’ months at sea, research shows.

Diagnosis

Vitamin C deficiency may be diagnosed with the combination of a physical examination and blood testing. Additionally, your doctor may test you for other nutrient deficiencies that sometimes coexist with vitamin C, including iron, calcium, folate, and vitamin B12 deficiencies. Imaging tests may be ordered for advanced cases where vitamin C deficiency has affected your bones, per the NCBI.

Treatment

Treatment of vitamin C deficiency may involve a combination of consuming vitamin C–rich foods and vitamin C supplements, with symptoms improving in the first 24 hours, according to the NCBI. Some adults with severe deficiencies may be provided with 1 to 2 grams of vitamin C for the first three days. Then your doctor may recommend 500 mg per day for up to one week, followed by 100 mg per day for the next three months.

While you might be concerned with preventing vitamin C deficiency, it’s also possible to get too much of the nutrient. That may lead to a different set of health concerns.

Causes

Ideally, the recommended amount of this micronutrient would come from a diet that is plentiful in vitamin C–rich foods, but the vitamin is also available in supplement form. Adults should be careful not to exceed large doses of 2,000 mg per day, as it can lead to gastrointestinal side effects including diarrhea, says the NIH.

Signs and Symptoms

According to the Mayo Clinic, other possible symptoms of vitamin C toxicity include:

• Abdominal cramps
• Headaches
• Heartburn
• Nausea
• Vomiting

Consequences

High doses of vitamin C might contribute to the formation of kidney stones, as well as increased risk of developing stomach problems, such as severe diarrhea, nausea, and gastritis. Previous research that looked at more than 23,000 men with no history of kidney stones found that those who took around 1,000 mg of ascorbic acid in supplement form had double the risk of developing kidney stones, compared with men who only took a multivitamin or men who didn’t take any dietary supplements. The increased risk of kidney stones was highest among men who took vitamin C at least once a day. The study authors note that the risk may not apply to women, who generally have a lower risk of kidney stones.

Another study looked at data on both men and women and concluded that higher levels of vitamin C, regardless of whether it came from diet or supplements, was significantly associated with a higher risk of incident kidney stones in men, but not among women. Those results were found in people who took high dose vitamin C with an intake greater than 700 mg per day.

Additionally, the NIH notes that the supplemental form of vitamin C has the potential to interact with several types of medications, including statins and certain chemotherapy drugs. People who are receiving chemotherapy, radiation therapy, or taking prescription medications should seek medical advice and discuss potential adverse effects with a doctor before taking vitamin C supplements.

Prevention

The best way you can help prevent vitamin C toxicity is to make sure you don’t exceed the recommended daily limits based on your age and sex. According to Oregon State University, that equates to no more than 2,000 mg per day for adults 19 years and older.

You can also help reduce your risk of toxicity by using foods as your primary source of your vitamin C intake. Only use supplements if recommended by your doctor.

Treatment

Vitamin C is a water-soluble vitamin, similar to B vitamins. Unlike fat-soluble nutrients, such as vitamins D and E, water-soluble vitamins are not stored in the body and must be taken in daily, according to Colorado State University. On the flip side, that also means vitamin C toxicity may be treated by eliminating excess amounts in your diet or by discontinuing supplements you may be taking.

Vitamin C is an essential micronutrient that we need to get through our diet, preferably through a variety of whole foods like fruits and vegetables. It plays a role in numerous important bodily functions, including immunity and skin health, and it may lead to a reduced risk of several chronic diseases, so getting your recommended daily allowance can help ensure that your body is working optimally.

Talk with a doctor or dietitian for advice if you’re concerned about your own vitamin C levels and whether you’re getting enough of this important nutrient. Also, seek medical advice before taking vitamin C for preventing or treating any condition, especially if you’re taking other supplements or medications.

Additional reporting by Jill Waldbieser.