What You Need to Know About Vitamin C

This essential nutrient supports nearly every aspect of health.

A collage of citrus fruits and vegetables that contain vitamin C

Centuries ago, sailors on long voyages often succumbed to a strange disease: Their muscles atrophied, their gums bled, their teeth fell out. The culprit was scurvy, caused by severe vitamin-C deficiency.

Mariners would subsist for months at sea on dried meat and hardtack, and C is found only in vegetables and fruits. After losing more sailors to scurvy than combat during the 18th century, the British navy realized it could prevent it by carrying limes onboard. A disease was cured, and the nickname “limey” was born.

Today, scurvy is relatively rare, but cases are still diagnosed, mainly in developed countries — including the United States, the United Kingdom, and Australia — where people often subsist primarily on processed foods instead of produce.

Vitamin C, or L-ascorbic acid, is much more than a scurvy preventive, though. It’s one of the body’s key antioxidants, supporting cell health and immune response — and that’s just a sampling of its positive attributes.

Even so, it can be easy to overlook how central vitamin C is to our health, largely because it’s hiding in plain sight. We know that we need it, but we don’t know why.

Here, learn the answers to some common questions about vitamin C — and how to get more of this vital nutrient in your diet.

What roles does vitamin C play in the body?

Vitamin C is a powerful multitasker. Its roles include the following:

  • Supporting the immune response.
  • Helping with protein metabolism and iron absorption.
  • Synthesizing collagen and helping to build connective tissue for blood vessels, cartilage, and muscle, making it essential to healthy bones, skin, and gums, as well as wound healing.
  • Protecting cells from oxidative stress, the cellular equivalent of an apple turning brown. Functional physician Gregory Plotnikoff, MD, calls vitamin C “the body’s Rust-Oleum.”
  • Contributing to the synthesis of carnitine, a compound the body uses to support energy metabolism. (Fatigue and lethargy are common symptoms of suboptimal vitamin-C levels.)
  • Supporting catecholamines like norepinephrine, which are involved in the stress response and help regulate blood sugar. (If you’re frequently “hangry,” Plotnikoff suggests upping your vitamin-C intake.)

How does vitamin C aid the immune system?

Vitamin C supports the immune response in several critical ways, one of which Plotnikoff likens to a janitor who mops up after an immune reaction storms through.

“Vitamin C supports the production and function of white blood cells,” he explains. When a type of white blood cell called a neutrophil encounters a problem microbe, it douses it in a shower of cells called superoxide radicals — a disinfecting substance Plotinkoff compares to chlorine bleach.

“One of the functions of white blood cells is to create and release the most powerful form of bleach on the planet, which is great for getting rid of bacteria, viruses, cancer, and the like,” Plotnikoff says. “If you’re spilling bleach everywhere, you need mops to clean up the damage. C is one of those mops.”

Free radicals have extra, unpaired electrons that create a vacuum, allowing them to “hoover up” unwanted cells, he explains. But left unchecked, these unstable cells attack everything in their path.

The immune response “releases free radicals that kill the virus, but kill our cells and tissues as well,” says functional-medicine physician Terry Wahls, MD.

Vitamin C helps to neutralize the aftereffects. It’s highly concentrated in neutrophils, helping them to kill the virus; afterward, it helps transform neutrophils by donating spare electrons to the “charged” free radicals, restoring them to a balanced state.

C is called an “antioxidant” because it halts oxidation after an infection.

How much vitamin C do I need daily?

Most animals produce their own vitamin C, but humans (along with other primates and, incidentally, guinea pigs) do not. We get vitamin C only from what we eat, specifically vegetables and fruits.

The recommended daily intake of vitamin C — the bare minimum to prevent deficiency and keep the body’s immune response operating properly — is 75 mg per day for an adult woman and 90 mg per day for an adult man. (Younger children need less, but those 14 and up also require 75 mg per day.)

Smokers, who are under greater oxidative stress than nonsmokers, are advised to consume an additional 35 mg daily. Plotnikoff suggests that smoking one cigarette may burn up as much as 25 mg of a body’s vitamin C on its own.

Functional providers tend to recommend significantly more than the RDA because of the vitamin’s essential role in handling oxidative stress. “For the average person who isn’t suffering from a chronic illness, I think aiming for 400 mg a day is reasonable,” Plotnikoff advises. “That’s doable by intentionally getting a lot of fresh produce in one’s diet. You don’t necessarily need supplementation.”

For those diagnosed with any chronic illness requiring the body to manage ongoing inflammation, he recommends as much as 1,000 mg per day.

The need for C also increases when everyday illnesses strike, adds Wahls. “The amount that you need daily if you’re well is lower than the amount you need if you’re not well,” she says.

You likely burn through your stores during any illness, so it’s wise to consume extra vitamin C afterward to rebuild them, ideally by upping your quotient of vegetables and fruits.

What are the signs and causes of vitamin-C deficiency?

True vitamin-C deficiency amounts to scurvy, whose hallmarks include extreme fatigue, weakness, and easy bruising and bleeding. The lethargy comes from insufficient synthesis of carnitine and the tissue damage from inadequate collagen synthesis. This is relatively rare.

Vitamin-C inadequacy, however, appears more common. It’s difficult to say precisely how common, because the last time the U.S. government measured serum levels of vitamin C on a large scale was in 2004, for the National Health and Nutrition Examination Survey. In that study of 7,277 participants, about 7 percent were found to be vitamin-C deficient — primarily smokers and low-income study participants, who may have had less local access to fresh produce.

Plotnikoff believes healthcare providers need to be looking more closely at vitamin-C status in patients suffering from unexplained health issues, given the complex role it plays in immunity and recovery. “We might be seeing deficiency but not know it,” he says, noting that in a Canadian study that tested the vitamin-C levels of hospitalized patients, only 20 percent had levels considered normal. That left 80 percent of hospitalized patients with suboptimal vitamin-C status, suggesting at least some possible relation between low levels and treatment-necessitating illness.

Some common risk factors for C deficiency include:

  • Inadequate dietary intake. It’s possible to develop vitamin-C deficiency on any limited diet, whether one is eating strictly fast food or restricting carbohydrate intake from vegetables and fruits.
  • Cigarette smoking. Multiple studies have found smokers to have one-third less circulating vitamin C than nonsmokers, on average, which is why they are often counseled to consume an additional 35 mg of vitamin C per day.
  • Chronic gastrointestinal (GI) issues. Illnesses such as Crohn’s and ulcer-ative colitis can block intestinal absorption of vitamin C from food.
  • Exposure to air pollution. Ozone, nitrogen dioxide, and other oxidants increase the need for antioxidants like vitamin C.
  • Type 2 diabetes. This condition has been linked to a greater need for vitamin C, possibly because of the oxidative stress caused by hyperglycemia.
  • Cancer treatments. Radiation and chemotherapy can trigger compromised immunity and lower circulating C.

Does vitamin C really help fight the common cold?

It depends. “There is some evidence that vitamin C can help shorten the duration of a cold,” says Plotnikoff. “But there is no clear evidence that it prevents a cold.”

Some studies indicate that increasing vitamin C intake can help reduce a cold’s duration by about 8 percent in adults and 14 percent in children. And other evidence has suggested people who endure heavy physical stress (marathon runners; those working in subarctic conditions) may develop fewer colds when they supplement with vitamin C.

Regardless of whether it reliably shortens a cold or reduces its symptoms, Plotnikoff and Wahls both suggest increasing vitamin C intake when you’re ill for any reason because the body uses more C to clean up after any inflammatory immune response.

Does vitamin C lower cancer risk?

A number of studies suggest a correlation between solid vitamin-C levels and lower cancer risk. The famed Nurses’ Health Study found a 63 percent risk reduction of breast cancer in women with a family history of disease when they consumed an average of 205 mg of vitamin C a day from food.

Other studies suggest vitamin C may help protect against GI cancers by lowering the amount of Helicobacter pylori bacteria in the gut, which may be a risk factor for these types of cancer.

Wahls is cautious about attributing these effects to vitamin C alone, however. She notes that supplement studies are usually inconclusive, and even when they show a benefit it is usually “not nearly as helpful as we’d have thought.”

She believes the synergistic effects of all the nutrients in whole foods — especially fresh vegetables and fruits, which are rich in vitamin C — are more likely responsible for any protective effects. “When you eat a food, it has many more bioavailable compounds than just vitamin C or any other nutrient,” she says.

“We don’t store it and we can’t make it,” says Wahls, so it’s critical to ensure you’re getting vitamin C daily.

As always, food is the first and best way to meet your body’s needs, both on a daily basis and when you’re ill. Eating a wide variety of colorful plant foods is the way to go. Pretty much all brightly colored vegetables and fruits provide a healthy dose of C, but some of the highest content is found in bell peppers, citrus fruits, dark leafy greens, broccoli, Brussels sprouts, and strawberries.

Also, vitamin C breaks down when vegetables are cooked, so make sure you consume some of your vegetables fresh or fermented to get the maximum C content.

Wahls favors fermented cabbage-family vegetables like sauerkraut and kimchi, which are high in vitamin C; the byproducts of fermentation are also good for the gut microbiome. (A cup of fermented red-cabbage kraut provides an astonishing 700 mg of vitamin C.)

So, what about orange juice? “It spikes blood sugar,” says Wahls. If you’re sick, that sugar may cancel out any benefits. She recommends adding lemon juice to water and tea instead, and eating peeled whole citrus fruits, because the fiber helps slow down the glycemic effect.

As for vitamin-C supplements, like those fizzy drink packets you chug when you feel a cold coming on? “I don’t see any downside to it,” says Plotnikoff. “It gives you 1,000 mg in one packet. But I tend to look at those as more marketing than magic. I wouldn’t want people to take it on a regular basis —then people are depending on a supplement rather than ensuring they’re getting a good balance in their diets. Fundamentals first.”

This article originally appeared at “Vitamin C: What You Need to Know” in the November 2020 issue of Experience Life.

is the Experience Life features editor.

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