ByBrian Handwerk
Published October 5, 2023
• 7 min read
When cold and flu season arrives, many people load up with a well-known defensive weapon—pills, powders, and all the other popular forms of vitamin C. The nutrient is one of a wide suite of supplements, from vitamin A to zinc, regularly taken by those hoping to boost their immune system and overall health. But vitamin C may also be one of the most overused.
Vitamin C really does help to boost the immune system and is an essential part of a healthy diet but its benefits are sometimes exaggerated. That leads many to megadose themselves with the nutrient which, while not usually dangerous, can be a waste of time and money.
Vitamin C’s superpower reputation really took hold in the 1970s with chemist Linus Pauling. The highly respected two-time Nobel Prize winner promoted the misconception that megadoses of vitamin C—to the tune of 3,000 mg a day—were the secret to eliminating the common cold and fighting off more serious ailments like heart disease and cancer, allowing people to live healthier and longer lives.
(Here’s the truth about other immune-boosting supplements.)
But Pauling’s vitamin C claims never stood up to rigorous research. “There is no consistent scientific evidence to support the idea that megadosing with vitamin C in prophylaxis and treatment of the common cold is effective,” explains Stefan Pasiakos, director of the NIH Office of Dietary Supplements.
However, scientific research has advanced since Pauling’s day, giving us greater insight into the real health benefits of vitamin C.
Can vitamin C cure or prevent a cold?
Most studies show that loading up on orange juice or supplements won’t do all that much against the common cold. In fact, taking many times more than the recommended daily amount—in the United States, that’s 90 mg a day for men and 75 mg for women—isn’t likely to make most people healthier generally. That’s because the body doesn’t absorb vitamin C as efficiently at doses above 1000 mg, and expels the excess in urine.
“Aside from people who have vitamin C deficiency or who are exposed to extreme physical exercise, high dose vitamin C has no benefit of preventing the common cold or reducing its symptoms,” says Christopher Duggan, professor of nutrition at Harvard T.H. Chan School of Public Health and director of the Center for Nutrition at Boston Children’s Hospital, citing a large body of evidence built up through many clinical trials.
(You probably aren’t getting enough vitamin D, though, experts say.)
Keeping current on vitamin C may help shorten the suffering a little, however. Research does suggest that people who take 1 to 2 grams of vitamin C per day may be sick with a cold for a bit less time, feeling better about 8 percent sooner as adults and 14 percent for kids.
So what does vitamin C do for the body?
While it’s certainly not a cure-all, vitamin C is definitely an essential nutrient with important health benefits. “It has many roles in the body,” says Duggan.
Vitamin C, also known as ascorbic acid, most famously delivers a key boost to the immune system. “Vitamin C supports the production of proteins, called interferons, that protect cells from viral attack,” Pasiakos explains. “Vitamin C also enhances the function of white blood cells, specifically phagocytes, that help engulf pathogens, and stimulate the activity of other immune cells to fight off infections.”
The body also uses vitamin C to form collagen, an important protein that helps to build bones, muscles, and strong blood vessels that protect against heart disease and stroke. Collagen is also essential for your skin—as a building block in the connective tissues that heal wounds and form scar tissue and well as to prevent sagging, wrinkling, dark spots, and acne. That’s why vitamin C is commonly used in skin care products. There is some evidence to show that vitamin C can even help protect from harmful effects of the sun when used in conjunction with sunscreen.
(Vitamin C, retinol, biotin? Here’s what your skin really needs.)
Vitamin C plays an intriguing role as an antioxidant, a compound that neutralizes free radicals in the body. Free radicals are unstable molecules with an odd number of electrons, prone to stealing electrons from the molecules in blood, skin, and other cells, damaging them and possibly contributing to the formation of diseases like cancer and heart disease. Because vitamin C and other antioxidants also have an odd number of electrons, they can absorb a free radical’s unpaired electron to prevent it from causing cell damage.
Finally, vitamin C helps make chemical messengers and hormones that are important in the brain and nervous system, including possible roles in reducing stress and anxiety. Researchers are also investigating its role in warding off cataracts or delaying their progression, and lowering uric acid levels that trigger gout.
How are you supposed to get enough vitamin C?
Humans must acquire vitamin C because the body does not make or store the nutrient. Serious deficiencies of vitamin C can result in that infamous bane of sailors, scurvy, “Severe deficiency of vitamin C can cause fatigue, growth delay, easy bleeding, excessive bruising and dental problems,” says Cory Fisher, a family medicine physician at the Cleveland Clinic. “One more reason that a well-balanced diet of real food is so important.
Fortunately most people do get plenty of vitamin C from the foods they eat. “Fruits and vegetables are nature’s best way of obtaining vitamin C,” says Jesse Bracamonte, a family medicine specialist with Mayo Clinic in Arizona. “Foods such as citrus (oranges, grapefruit, lemons), bell peppers, tomatoes, and cruciferous vegetables (broccoli, cabbage, cauliflower) are great sources.” The nutrient is even found in fortified foods like breakfast cereals.
(The Mediterranean diet has stood the test of time for a reason: It works.)
In the United States a normal diet should be enough to meet the recommended dietary allowance. “Ideally an orange, or a cup of strawberries has enough vitamin C for the day,” Bracamonte says. Smokers require an additional 35 mg a day, since the habit depletes the body’s ability to absorb vitamin C.
Vitamin C can also be sourced from a wide variety of nutritional supplements, which may be particularly helpful for those who don’t eat many fruits and veggies, or are at risk for deficiency due to heavy drinking or smoking, or because of health conditions like people who are on dialysis. While the supplements do deliver vitamin C to the body, they may not contain all the other nutrients found in healthy foods.
Is there such a thing as too much vitamin C?
Vitamin C has an upper limit of 2000 mg a day for adults. Most people can tolerate overdoing it but those with kidney issues should be wary, while others might experience unpleasant stomach issues and diarrhea or even, rarely, decreased effectiveness of certain drugs like statins taken to control high cholesterol.
And while vitamin C also strengthens the gums, it can have a downside for oral hygiene: Chewable vitamin C supplements are acidic and, when left too long in the mouth, can lead to tooth erosion.
Duggan explains that while getting enough vitamin C is important, there’s simply little point in overdoing it. “Unless you are at risk of vitamin C deficiency, most people can meet their dietary needs with food,” he says. “In general, health and nutrition are optimized by a well-rounded diet versus reliance on supplements.”
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