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 find and destroy pathogens. Adults need 75 to 90 mg per day, an amount easily reached through diet, yet many people still fall short. Here’s what this essential nutrient actually does inside your body and how to get enough of it.
Immune Support: What Vitamin C Actually Does
Vitamin C plays a hands-on role in your immune response rather than just giving it a vague “boost.” When your body detects an infection, immune cells called neutrophils and macrophages rush to the site. Vitamin C helps guide that migration, essentially improving your immune system’s aim. Once those cells arrive, they destroy pathogens by releasing bursts of highly reactive molecules. Vitamin C then protects the immune cells themselves from the collateral damage of that chemical attack.
It also supports your adaptive immune system, the slower but more targeted branch. Vitamin C stimulates the development of T cells from their immature precursors into fully functional mature cells, and this effect scales with dose: more vitamin C means more T cell production, up to a point.
The practical payoff is modest but real. A large Cochrane review covering nearly 10,000 cold episodes found that people who took vitamin C regularly (not just after getting sick) had shorter colds: about 8% shorter in adults and 14% shorter in children. That translates to roughly half a day less of symptoms for adults. Starting vitamin C after cold symptoms appear, however, showed no consistent benefit. So regularity matters more than rescue dosing.
Collagen Production and Skin Health
Collagen is the most abundant protein in your body. It forms the structural framework of your skin, tendons, blood vessels, and bones. Your body cannot build stable collagen without vitamin C. The vitamin acts as a required helper molecule during a key step in collagen assembly: it enables the chemical modification of proline, an amino acid, into hydroxyproline. Hydroxyproline is what locks collagen’s signature triple-helix structure into place, giving it strength and stability. Without that step, collagen molecules are unstable and poorly secreted from cells.
This is why scurvy, the disease caused by severe vitamin C deficiency, shows up as bleeding gums, slow wound healing, and fragile skin. These are all tissues that depend on constant collagen turnover. Even mild deficiency can impair wound healing before any dramatic symptoms appear.
Helping Your Body Absorb Iron
If you eat a mostly plant-based diet, vitamin C is one of the most important nutrients on your plate. Plants contain a form of iron called non-heme iron, which your gut absorbs poorly on its own. Vitamin C dramatically changes this. In one study, iron absorption increased from less than 1% to over 7% as vitamin C was added to a meal, an almost ninefold improvement.
Timing is critical. Vitamin C needs to be in your stomach at the same time as the iron-containing food. Taking it four to eight hours before a meal showed significantly less benefit. So pairing a glass of orange juice with an iron-rich meal like lentils or spinach is a practical, effective strategy for preventing iron deficiency.
Antioxidant Protection
Your cells constantly produce free radicals as byproducts of normal metabolism, and environmental factors like pollution and UV exposure add more. These unstable molecules damage DNA, proteins, and cell membranes. Vitamin C directly neutralizes free radicals by donating electrons to stabilize them. It’s one of the body’s primary water-soluble antioxidants, meaning it works in your blood and inside cells rather than in fatty tissues.
This antioxidant activity also underpins many of vitamin C’s other roles. The protection it offers neutrophils during an immune response, for instance, is fundamentally an antioxidant function.
Blood Pressure and Heart Health
A meta-analysis of randomized controlled trials found that vitamin C supplementation lowered systolic blood pressure (the top number) by about 3.8 mm Hg and diastolic pressure (the bottom number) by about 1.5 mm Hg. In people who already had high blood pressure, the systolic reduction was larger: nearly 5 mm Hg. These are not dramatic numbers on their own, but reductions in that range, sustained over years, are associated with meaningful drops in cardiovascular risk at a population level. Vitamin C likely contributes to these effects by supporting the function of blood vessel walls and reducing oxidative stress in the cardiovascular system.
Best Food Sources
You don’t need supplements to hit your daily target. Many common foods provide well over a full day’s worth in a single serving:
- Orange juice (frozen concentrate, 1 cup reconstituted): roughly 95 to 125 mg
- Red bell pepper (half a cup, raw): about 95 mg
- Broccoli (half a cup, cooked): about 50 mg
- Strawberries (half a cup): about 50 mg
- Tomato juice (1 cup): about 170 mg
Black currants are a lesser-known powerhouse, packing over 200 mg per cup. Kiwi, papaya, and Brussels sprouts are also excellent sources. Since vitamin C breaks down with heat, raw or lightly cooked preparations preserve more of it.
How Much You Need
The recommended daily intake is 90 mg for adult men and 75 mg for adult women. Smokers need an extra 35 mg per day because smoking accelerates the breakdown of vitamin C in the body. Pregnancy and breastfeeding also increase requirements.
The upper limit for adults is 2,000 mg per day. Going beyond that doesn’t provide added benefit and commonly causes digestive problems like diarrhea, nausea, and stomach cramps. Very high doses over long periods may also increase the risk of kidney stones in susceptible individuals. Because vitamin C is water-soluble, your body excretes what it doesn’t need through urine, which means megadoses are largely wasted rather than stored. For most people, a varied diet with several servings of fruits and vegetables provides more than enough.