What Does Vitamin C Do? Immune Health, Skin Benefits, and More

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Dr. Ellen Albertson, PhD, RDN, NBC-HWC Posted on June 21, 2023

Vitamin C has a fascinating history and many important functions, from preventing scurvy and boosting the immune system to zapping free radicals. Feel like you’re catching a cold? Perhaps you reach for a glass of vitamin C-rich orange juice or take a vitamin C supplement when the sniffles start.

But did you know vitamin C can do much more? Made by all plants and animals, vitamin C may help boost mental vitality, improve sleep, and give you glowing skin when used topically. Plus, it can regenerate vitamin E and is needed to make collagen and absorb iron.

Read on to discover what this powerful micronutrient is and does.

What Is Vitamin C?

Also known as ascorbic acid, vitamin C is a water-soluble vitamin-like the B complex—B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 pyridoxine, B7 (biotin), B9 (folate), and B12 (cobalamin). Like all vitamins, vitamin C acts as a cofactor or “helper molecule” that catalyzes many metabolic reactions.

Unlike the four fat-soluble vitamins (A, D, E, and K), vitamins C and B complex dissolves in water rather than fat. While fat-soluble vitamins are slowly absorbed and transported through the bloodstream by fat globules, vitamin C is quickly absorbed from the intestines and used by the body. Excess amounts are eliminated from the blood within three to four hours, so it’s best to consume vitamin C throughout the day or take a time-released supplement.

Like all essential vitamins, vitamin C is an organic compound we need to consume in small amounts because our bodies cannot make it. Most animals can make vitamin C from glucose (blood sugar) in the liver or kidneys. The exceptions are humans and some other primates, guinea pigs, capybaras, and certain bats.

Millions of years ago, our ancestors lost the ability to synthesize vitamin C. Scientists are still determining why this happened. One theory is that our ancestor’s diet was so rich in vitamin C that they no longer needed to synthesize it themselves. Since making vitamin C requires fuel, losing the ability may have been advantageous because it conserved energy. Other researchers propose that a retrovirus inactivated a gene, which blocked the final step needed to make vitamin C from glucose.

Vitamin C Food Sources

Vitamin C is found in many fruits and vegetables. Good sources include:

Citrus fruits like oranges, lemons, limes, and grapefruit
Cantaloupe
Bell peppers
Chili peppers
Guavas
Black currants
Tomatoes
Berries
Pineapple
Kiwi
White potatoes
Cruciferous vegetables like kale, broccoli, and cabbage

Some foods and beverages are also fortified with vitamin C. An Australian superfood, the Kakadu plum, is the richest source and contains about 100 times more vitamin C than oranges.

An unstable nutrient, vitamin C, is easily destroyed by heat and light or lost in cooking water. You can minimize losses by eating raw fruits and vegetables or steaming vegetables in a double boiler rather than boiling them in water.

Having trouble getting enough vitamin C from diet alone? Vitamin C supplements, usually made from ascorbic acid or rose hips, can be taken as capsules, pills, or powder. Good multivitamin formulas generally contain at least the RDA for vitamin C, which is 75 mg for women and 90 mg for men. Pregnant women over age 18 have an RDA of 85mg, and lactating women have an RDA of 120mg. The upper recommended limit for vitamin C is 2,000 mg a day. Taking more than that can result in GI issues such as stomach pain and diarrhea.

Vitamin C is often found in immune boosting and wellness formulas, along with ingredients like elderberry, probiotics, the medicinal mushroom reishi, and zinc. Since vitamin C can increase iron absorption from plant sources, it’s often added to iron supplements. You can also find it as an ingredient in antioxidant formulas and together with vitamin E because the two work synergistically to reduce oxidative stress. Studies also suggest that vitamin C “recycles” vitamin E, so it lasts longer.

Smokers, people exposed to secondhand smoke, individuals who don’t eat a variety of foods, and people with certain medical conditions, including chronic disease, digestive disorders, and kidney disease requiring dialysis, may need more vitamin C. Stress and alcohol use can also increase how much you need.

According to the National Institutes of Health, vitamin C deficiency is rare in the United States and Canada. People who consume under 10 mg per day can develop scurvy.

Written about as early as 1500 BC and described by Aristotle, scurvy was once a huge problem and widespread illness for sailors on long voyages who ate little produce. A couple of months into their voyage, they would experience fatigue, weakness, tooth loss, and bruising. Once they landed and started eating citrus fruits, the illness disappeared.

Vitamin C was chemically identified in 1920 by Albert von Szent Györgyi, who realized it could cure and prevent scurvy. He named it ascorbic acid because “ascorbic” means “anti-scurvy.”

Key For Collagen Formation

One of the most important functions of vitamin C is the formation and maintenance of collagen, the most abundant protein in the body. Collagen has a fiber-like structure and is the basis of connective tissue. (The word “collagen” comes from kolla, Greek for glue.) Found in skin, ligaments, tendons, cartilage, capillary walls, muscles, intervertebral discs, bones, and teeth, collagen provides the body with structure and support and is required for wound healing. Vitamin C is needed to transform two essential amino acids—proline and lysine—into hydroxyproline and hydroxylysine, which structure collagen.

Collagen is also found in several foods, including gelatin and bone broth, and can be taken as a supplement. Taking collagen as a supplement may have health benefits, especially as we age because production naturally declines with age. Possible benefits of taking collagen include improved skin appearance and elasticity, less joint pain and bone loss, and increased muscle mass.

Healthy Skin Benefits

Vitamin C is essential for skin health because of its role in making collagen, one of skin’s main components. As an antioxidant, vitamin C also helps prevent the formation of free radicals that can damage the skin. While wearing sunscreen and limiting sun exposure is always a good idea, vitamin C can also help prevent harm caused by ultraviolet radiation.

Taking vitamin C in combination with other ingredients may support skin health. One study found that consuming a combination of vitamin C, collagen, acerola fruit extract, zinc, biotin, and a vitamin E complex for twelve weeks resulted in positive skin changes, including increased hydration, thickness, and elasticity.

Vitamin C is a darling of the skincare world and is frequently added to skin care products like serums, cleansers, moisturizers, and sunscreens. Generally considered safe when used topically, vitamin C is absorbed by the upper layers of the skin, where it can work directly to improve skin appearance and texture.

Vitamin C benefits the skin in several specific ways when applied topically:

Increases collagen and elastin: Vitamin C may turn back the clock by increasing the production of collagen and elastin, resulting in firmer, smoother, younger-looking skin.
Lightens dark spots: Vitamin C may reverse hyperpigmentation, dark spots on the skin that tend to occur over time when you have too much sun exposure. In an analysis of 31 randomized controlled clinical trials, vitamin C effectively reduced pigmentation induced by UV daylight-simulated exposure. It may also help prevent signs of photoaging.
Reduces redness: As an antioxidant with anti-inflammatory properties, vitamin C may also reduce redness associated with skin issues like rosacea and eczema.
Conceals dark circles under eyes: Noticing dark circles from lack of sleep? Topical eye creams containing vitamin C may help. A small study found that applying a lotion containing vitamin C for 6 months thickened the lower eyelid skin, helping to conceal dark circles.

The most concentrated topical form of vitamin C is found in serums. For best results, follow the directions on the package. If you have sensitive skin, do a patch test or start with a small dose to see how your skin responds.

Bounce Back Quicker From the Common Cold

Back in the 1970s, Nobel Prize winner Linus Pauling claimed that taking vitamin C could significantly reduce the incidence and duration of the common cold. However, his research was based primarily on one study conducted on school children.

Fast forward five decades, and we now know that Pauling was partially correct. The current consensus is that while taking a vitamin C supplement won’t prevent you from catching a cold, consuming doses at or above 200 mg a day decreases how sick you get and how long your cold lasts—especially if you start supplementation within 24 hours of feeling ill and continue for 5 days. Research also suggests people with high physical stress, such as marathon runners, who regularly take vitamin C could cut their risk of getting a cold by 50 percent.

Supports the Immune System

Research suggests that vitamin C is essential for a well-functioning immune system and that deficiency increases the risk of infections. In addition, infections tend to decrease levels of vitamin C, which is why it’s especially important to consume adequate amounts when you are sick.

Innate Immunity

Vitamin C supports both your innate and adaptive immune system. It supports innate immunity by keeping your skin and mucous membranes—the main barriers to infection—healthy so pathogens can’t enter the body. As an antioxidant, vitamin C helps prevent the creation of free radicals that can cause cellular damage and disease.

Adaptive Immunity

Vitamin C supports adaptive immunity by enhancing the impact of frontline defenders, like neutrophils and white blood cells, that kill and digest microorganisms like bacteria and viruses at infection sites before they can negatively impact the body. Vitamin C also appears to boost the production of lymphocytes, which produce antibodies and coordinate how your immune system works so you are less susceptible to infections.

Chronic Inflammation

As a powerful antioxidant, vitamin C can also help reduce chronic inflammation. Chronic inflammation occurs when your immune system is continuously activated in the absence of danger. It is involved in many diseases, including type 2 diabetes, heart disease, rheumatoid arthritis, psoriasis, and Alzheimer’s.

By neutralizing damaging free radicals, vitamin C can help reduce triggers of inflammation. A randomized controlled trial of patients with hypertension and/or diabetes found that taking 500 mg of vitamin significantly reduced several inflammatory markers.

Promotes Eye Health

Vitamin C may help fight age-related macular degeneration (AMD) and cataracts—two leading causes of blindness later in life. While it doesn’t reduce the risk of AMD, vitamin C taken with additional nutrients may slow AMD progression. A study of older people with AMD with a high risk of the disease progressing found that taking 500 mg of vitamin C, 400 IUs of vitamin E, 15 mg of beta-carotene, and 2 mg of copper for approximately 6 years experienced less vision loss and risk of the disease getting worse.

While additional studies are needed, some research suggests that people who consume more vitamin C from dietary sources have a lower risk of developing cataracts.

Improves Sleep

Sleep is key to restoring your body and mind and maintaining good health. Unfortunately, about a third of Americans don’t regularly get the recommended seven or more hours of quality sleep per night. Vitamin C, probably because it’s a powerful antioxidant, appears to impact sleep duration and quality positively and may also help with obstructive sleep apnea and restless leg syndrome.

More research is connecting free radical damage and oxidative stress with sleep issues and disorders. The National Health and Nutrition Examination Survey (NHANES) showed that people who sleep the least—five to six hours—have the lowest intake of lutein, zeaxanthin, selenium, and vitamin C, all of which are antioxidants.

Restless leg syndrome, a disorder where people experience unpleasant sensations in the legs, especially at night, can disrupt sleep. Research has shown that Vitamin C combined with vitamin E reduces the symptoms of restless leg syndrome in hemodialysis patients.

Obstructive sleep apnea is a sleep and breathing disorder that affects up to 20% of people and increases the risk of cardiovascular disease and strokes. Studies suggest that vitamin C and E improve the quality of life for people with sleep apnea, decrease daytime sleepiness, and result in longer sleep duration.

Enhances Brain Health

Feeling tired or losing focus at work? Vitamin C may help. Your brain has the highest concentration of vitamin C in the body, depends on vitamin C to work properly, and needs C to make several neurotransmitters.

Inadequate levels of vitamin C are associated with less mental vitality. Studies also suggest that vitamin C deficiency may affect cognitive impairment, depression, and confusion. A population study of adults between 20 and 39 found that blood levels of vitamin C were associated with attention levels.

Another randomized controlled trial found that subjects who took 500 mg of vitamin C daily for four weeks showed significant improvement in attention, work absorption, and fatigue and had better scores on a word test than those in the placebo group.