Vitamin C is an essential nutrient that your body cannot produce on its own, so you need to get it from food or supplements every day. It plays a direct role in immune defense, collagen production, iron absorption, and antioxidant protection throughout the body. The recommended daily intake is 90 mg for adult men and 75 mg for adult women, with smokers needing an additional 35 mg per day.
Collagen Production and Tissue Repair
One of vitamin C’s most fundamental jobs is building collagen, the structural protein that holds together your skin, bones, tendons, blood vessels, and cartilage. Vitamin C is required for a chemical step called hydroxylation, which stabilizes collagen molecules so they can form strong, supportive fibers outside of cells. Without this step, collagen becomes unstable, and tissues literally start to fall apart.
This is why wound healing slows down when vitamin C levels are low. Your body relies on a steady supply to lay down new collagen at injury sites. The same mechanism explains why vitamin C deficiency eventually leads to bleeding gums, loose teeth, and poor scar formation. It’s not just a building block for repair; it’s the tool that makes repair structurally sound.
Antioxidant Protection
Vitamin C is one of the body’s primary water-soluble antioxidants. It neutralizes free radicals, which are unstable molecules generated by normal metabolism, pollution, UV radiation, and cigarette smoke. Left unchecked, free radicals damage DNA, proteins, and cell membranes, contributing to aging and chronic disease. Vitamin C scavenges these molecules directly and also regenerates other antioxidants (like vitamin E) so they can continue working.
This antioxidant role is partly why smokers need more vitamin C. Cigarette smoke floods the body with free radicals, depleting vitamin C stores faster than in nonsmokers.
Blood Vessel Function
Vitamin C helps keep blood vessels flexible by protecting nitric oxide, a molecule that signals arteries to relax and widen. In people with high blood pressure, free radicals break down nitric oxide before it can do its job, causing blood vessels to stay constricted. Research published in the American Heart Association’s journal Circulation found that vitamin C improved blood vessel dilation in hypertensive patients by shielding nitric oxide from destruction. In people with normal blood pressure, there was no additional benefit, suggesting vitamin C corrects a problem rather than enhancing an already healthy system.
Immune Function
Vitamin C supports multiple layers of immune defense. It strengthens the skin barrier, your first line of protection against pathogens. Inside the body, it accumulates in white blood cells, helping them move toward infections, engulf bacteria, and kill invaders. It also promotes the production and function of lymphocytes, the immune cells responsible for targeted responses to specific threats.
The popular belief that megadoses of vitamin C prevent colds is overstated. Regular supplementation modestly reduces how long colds last (roughly by a day in adults) but doesn’t reliably prevent them in the general population. People under intense physical stress, like marathon runners or soldiers in subarctic conditions, do see a meaningful reduction in cold frequency with daily vitamin C, likely because their baseline demands are higher.
Iron Absorption
Vitamin C dramatically improves the absorption of non-heme iron, the form found in plant foods like spinach, lentils, and fortified cereals. It converts iron into a chemical form that your gut can absorb more easily. Pairing a vitamin C-rich food (citrus, bell peppers, strawberries) with an iron-rich meal can increase absorption several-fold. This matters most for vegetarians, vegans, and anyone at risk for iron-deficiency anemia.
Skin Health
Beyond its internal collagen role, vitamin C has measurable effects on skin when applied topically. Formulations containing 3 to 10 percent vitamin C, used consistently for at least 12 weeks, have been shown to decrease wrinkling, reduce roughness, and increase collagen production in the skin. Topical vitamin C also mildly lightens hyperpigmentation by reducing melanin production and melanin oxidation.
Vitamin C provides some protection against UV damage, though not in the way sunscreen does. It doesn’t absorb UV light. Instead, it neutralizes the free radicals that UV exposure generates, reducing downstream cell damage. Studies show that combining vitamin C with vitamin E topically is significantly more effective at preventing photodamage than either vitamin alone. Oral vitamin C by itself doesn’t meaningfully increase sun protection, but oral combinations of C and E do raise the skin’s threshold for sunburn.
What Happens When You Don’t Get Enough
Mild vitamin C deficiency can cause fatigue, irritability, and slow wound healing before any dramatic symptoms appear. Severe deficiency over at least three months causes scurvy, a condition that was historically common among sailors on long voyages. Early symptoms include weakness and joint pain. As it progresses, you may develop a characteristic rash of red or blue spots caused by bleeding under the skin, along with swollen and bleeding gums, loose teeth, and poor wound healing. Scurvy is rare in developed countries but still occurs in people with extremely restricted diets, certain digestive conditions, or chronic alcoholism.
Absorption and Upper Limits
Your body absorbs vitamin C efficiently at normal dietary doses, but absorption decreases as intake climbs. At doses around 200 mg, the intestines absorb nearly all of it. At 500 mg and above, a progressively smaller percentage gets through, and your kidneys excrete the excess in urine. This means taking massive doses doesn’t proportionally raise blood levels; your body simply discards what it can’t use.
The tolerable upper limit for adults is 2,000 mg per day. Going above this regularly can cause diarrhea, nausea, stomach cramps, and in some people, kidney stones. If you’re taking a supplement, splitting a large dose into smaller amounts throughout the day improves absorption compared to taking it all at once.
Best Food Sources
You can meet your daily needs easily through food. A single medium orange provides about 70 mg, and a cup of raw red bell pepper delivers over 190 mg, more than double the daily requirement. Other strong sources include kiwi, strawberries, broccoli, Brussels sprouts, and cantaloupe. Cooking reduces vitamin C content since it’s sensitive to heat and water, so raw or lightly cooked preparations preserve more of the nutrient.