Vitamin C plays a central role in immune defense, tissue repair, iron absorption, and protecting cells from damage. It’s an essential nutrient, meaning your body can’t produce it, so you need a steady supply from food or supplements. The recommended daily intake is 90 mg for men and 75 mg for women, with smokers needing an extra 35 mg per day.
How It Supports Your Immune System
Vitamin C is concentrated in immune cells, particularly neutrophils, the white blood cells that serve as your body’s first responders to infection. These cells travel to infection sites, engulf bacteria, and destroy them using bursts of reactive chemicals. When vitamin C levels are adequate, this entire process works more efficiently. One clinical study found that dietary vitamin C supplementation produced a 20% increase in neutrophil chemotaxis, the ability of these immune cells to migrate toward threats.
In people with genetic defects in neutrophil function, vitamin C supplementation has been shown to reduce the frequency of infections and improve the bacteria-killing capacity of their immune cells. On the other end, severe vitamin C deficiency in animal models is linked to weaker oxidative bursts, the mechanism neutrophils use to destroy pathogens once they’ve captured them.
Collagen and Tissue Repair
Collagen is the most abundant protein in your body. It forms the structural framework of skin, tendons, ligaments, blood vessels, and bones. Vitamin C helps enzymes modify the amino acids proline and lysine during collagen production, a step necessary for collagen fibers to fold into their stable, rope-like structure. Without this modification, collagen is weak and fragile, which is why severe deficiency eventually causes bleeding gums, poor wound healing, and joint pain.
This role in collagen production is why vitamin C matters for wound healing and skin integrity. Your body is constantly building and repairing connective tissue, and adequate vitamin C keeps that process running smoothly.
Iron Absorption
If you get your iron from plant-based sources like spinach, lentils, or fortified cereals, vitamin C can dramatically improve how much of it your body actually absorbs. Plant-based (non-heme) iron is poorly absorbed on its own. Research shows that iron absorption increases from 0.8% to 7.1%, nearly a ninefold jump, when increasing amounts of vitamin C are added to a meal containing non-heme iron. Even a modest amount helps. Pairing iron-rich foods with a glass of orange juice or some bell pepper at the same meal is one of the simplest ways to boost your iron status.
Blood Vessel Function
Your blood vessels rely on a molecule called nitric oxide to relax and widen, which helps regulate blood pressure and blood flow. Free radicals in the bloodstream break down nitric oxide before it can do its job, and vitamin C neutralizes those free radicals. In people with high blood pressure, vitamin C has been shown to restore this process, improving the ability of blood vessels to dilate. When researchers blocked nitric oxide production, vitamin C’s benefit on blood vessel relaxation disappeared, confirming that the effect works specifically by protecting nitric oxide from destruction.
Skin Protection
Vitamin C protects skin cells from ultraviolet damage, but not in the way sunscreen does. It doesn’t absorb UV light. Instead, it neutralizes the free radicals that UV exposure generates inside skin cells, reducing the chain of oxidative damage that leads to sunburn, premature aging, and DNA mutations.
Oral vitamin C alone doesn’t provide meaningful sun protection. Studies measuring minimal erythemal dose (the amount of UV needed to cause redness) found no significant increase from vitamin C supplements taken by mouth. However, combining oral vitamin C with vitamin E does increase photoprotection, suggesting the two antioxidants work together in skin.
Topical vitamin C is a different story. Applied directly to the skin, it reaches higher local concentrations. In animal studies, topical vitamin C reduced sunburned cells, decreased redness, and limited UV-induced DNA damage. Combining topical vitamin C and E outperforms either one alone. For topical products, formulations with a pH below 4.0 and concentrations around 20% achieve the best absorption into skin. Higher concentrations don’t absorb better.
What Happens When You Don’t Get Enough
Early vitamin C deficiency shows up as general weakness, fatigue, irritability, and aching joints. These symptoms can develop within a few months of consistently low intake. Left untreated, deficiency progresses to scurvy: bleeding gums, loosened teeth, and spontaneous bleeding under the skin. Scurvy is rare in developed countries but still occurs in people with extremely limited diets, such as those eating almost no fruits or vegetables for extended periods.
How Your Body Processes Vitamin C
Vitamin C is water-soluble, so your body doesn’t store large reserves. Excess is filtered out by the kidneys and excreted in urine. This means consistent daily intake matters more than occasional large doses.
Standard vitamin C supplements (ascorbic acid) are well absorbed at typical doses. Liposomal formulations, which wrap vitamin C in fat-based particles, show about 30% higher overall absorption compared to regular ascorbic acid at a 1,000 mg dose. Liposomal forms also maintain higher blood levels at 10 and 24 hours after taking them. That said, both forms reach peak blood levels at roughly the same time, around 2.5 hours. For most people eating a reasonable diet and taking standard-dose supplements, regular ascorbic acid works fine.
How Much You Need
The recommended daily allowance is 90 mg for adult men and 75 mg for adult women. Smokers need 35 mg more per day because smoking increases oxidative stress and depletes vitamin C faster. A single medium orange provides about 70 mg, so meeting the requirement through food is straightforward if you regularly eat fruits and vegetables. Bell peppers, strawberries, broccoli, and kiwifruit are all rich sources.
The tolerable upper limit for adults is 2,000 mg per day. Going above that consistently can cause digestive problems like diarrhea, nausea, and stomach cramps. Very high doses may also increase the risk of kidney stones in people who are predisposed to them. Since your body excretes what it can’t use, megadoses mostly end up in urine rather than providing additional benefit.