Vitamin C supports your body in a surprisingly wide range of ways, from building the protein that holds your skin together to helping your immune cells hunt down bacteria. It’s both an antioxidant and an essential cofactor for dozens of enzymatic reactions, which is why running low on it affects so many systems at once. Here’s what it actually does and how much you need.
Collagen Production and Tissue Repair
Collagen is the most abundant protein in your body. It’s the structural scaffolding for your skin, tendons, ligaments, blood vessels, and bones. Vitamin C is required for a specific step in collagen assembly: it helps attach oxygen and hydrogen atoms to the amino acid proline, creating hydroxyproline, which stabilizes collagen’s signature triple-helix shape. Without enough vitamin C, your body still makes collagen, but the molecules are unstable and can’t do their job properly.
This is why vitamin C deficiency shows up so visibly. Wounds stop healing, old scars can reopen, gums bleed, and skin bruises easily. These are all signs that collagen turnover has stalled. On the flip side, adequate vitamin C intake keeps this repair cycle running smoothly, which matters for everything from post-surgery recovery to everyday skin maintenance.
Immune System Support
Vitamin C stimulates both the production and function of white blood cells, particularly neutrophils, the front-line cells that attack foreign bacteria and viruses. It improves how quickly these cells move toward an infection site, how effectively they engulf pathogens, and how well they generate the oxidants used to kill invaders. It also increases levels of antibodies circulating in your blood.
There’s an interesting catch, though. Immune cells generate a burst of damaging molecules when they attack a pathogen, and those same molecules can harm the immune cells themselves. Vitamin C protects white blood cells from this self-inflicted oxidative damage, essentially keeping the soldiers healthy while they fight.
The practical effect on colds is modest but real. A large Cochrane review found that people who take vitamin C regularly (not just when they feel a cold coming on) experience colds that are about 8% shorter in adults and 14% shorter in children. At higher doses of 1 to 2 grams per day, children’s colds were 18% shorter. Cold severity also decreased. Taking vitamin C after symptoms start, however, doesn’t appear to make much difference.
Antioxidant Protection
Vitamin C is the primary water-soluble antioxidant in your blood and tissues. It works by readily donating electrons to unstable molecules called free radicals, neutralizing them before they can damage proteins, fats, DNA, and other critical cell components. These free radicals come from normal metabolism, immune activity, air pollution, cigarette smoke, and UV radiation.
Vitamin C also recycles other antioxidants in your body, including vitamin E. Once vitamin E neutralizes a free radical in a cell membrane, it’s spent. Vitamin C can regenerate it, effectively doubling the antioxidant’s usefulness. This teamwork between water-soluble vitamin C and fat-soluble vitamin E means the two vitamins protect different parts of your cells while reinforcing each other.
Iron Absorption
If you eat plant-based iron sources like spinach, lentils, or fortified cereals, vitamin C can dramatically improve how much iron your body actually absorbs. Plant foods contain non-heme iron, which is in a chemical form (ferric iron) that your intestinal cells can’t take up directly. Vitamin C converts it to the form your gut can absorb (ferrous iron) and also wraps around iron molecules to keep them soluble as they move from the acidic environment of your stomach into the more alkaline small intestine.
The effect is dose-dependent. Research has shown that iron absorption from a meal increases from 0.8% to 7.1%, nearly a ninefold jump, when vitamin C is added in amounts ranging from 25 to 1,000 mg. Even a glass of orange juice with an iron-rich meal makes a measurable difference. This is especially relevant for vegetarians, vegans, and anyone with low iron stores.
What Happens When You Don’t Get Enough
Going without adequate vitamin C for at least three months can cause scurvy, a condition that was historically common among sailors on long voyages. Early symptoms include fatigue, swollen or bleeding gums, and slow wound healing. As it progresses, hair becomes dry and coils into corkscrew shapes, previously healed wounds can reopen, teeth loosen, and bleeding occurs under the skin. In children, scurvy can cause irritability, pain with movement, poor appetite, and failure to gain weight.
Full-blown scurvy is rare in developed countries today, but subclinical deficiency (low levels that don’t produce obvious symptoms) is more common than you might expect. Smokers are at particular risk because smoking accelerates vitamin C depletion.
How Much You Need
The recommended daily intake is 90 mg for adult men and 75 mg for adult women. During pregnancy that rises to 85 mg, and during breastfeeding to 120 mg. Smokers need an additional 35 mg per day on top of the standard recommendation because of increased oxidative stress.
Getting enough from food is straightforward. A single cup of orange juice from frozen concentrate provides well over 300 mg. A cup of tomato juice has about 170 mg. Black currants deliver around 200 mg per cup. Bell peppers, strawberries, broccoli, and kiwifruit are also excellent sources. Two kiwifruit per day provide roughly 259 mg, more than enough to meet and exceed the daily target.
Upper Limits and Side Effects
Because vitamin C is water-soluble, your body excretes what it doesn’t need through urine. This makes toxicity uncommon, but high-dose supplements (often marketed at 500 to 2,000 mg per serving) can still cause problems. Doses above 2,000 mg per day frequently trigger digestive issues like nausea, diarrhea, and stomach cramps.
A more serious concern involves kidney stones. Research published through Harvard Health found that taking high-dose vitamin C supplements appears to double a man’s risk of developing calcium oxalate kidney stones. If you have a history of kidney stones, high-dose supplements are worth avoiding. For most people, getting vitamin C from food or a modest supplement keeps you well within safe territory and covers all the roles this vitamin plays in your body.