Ascorbic acid is the chemical name for vitamin C, a water-soluble nutrient your body cannot produce on its own. You get it entirely from food or supplements, and your intestines absorb it through specialized transport proteins that pull it across cell membranes. Adults need between 75 and 120 mg per day depending on sex and life stage, with smokers needing an extra 35 mg daily.
How Your Body Absorbs Ascorbic Acid
Your intestinal cells use dedicated transport proteins called sodium-dependent vitamin C transporters (SVCTs) to pull ascorbic acid from your gut into your bloodstream. These transporters work like tiny elevators: they grab two sodium ions and one vitamin C molecule at a time, using the natural flow of sodium across the cell membrane to power the process. This 2:1 ratio of sodium to vitamin C is consistent across both known transporter types, SVCT1 and SVCT2.
The process is dose-dependent, which means your body absorbs a smaller percentage of vitamin C as the dose increases. At typical dietary amounts (30 to 180 mg), absorption rates are high. But if you take a large supplement of 1,000 mg or more, a significant portion passes through unabsorbed and is excreted. This is why splitting a high dose into smaller amounts throughout the day delivers more vitamin C to your cells than taking it all at once.
What Ascorbic Acid Does in Your Body
Vitamin C’s most well-known role is in building collagen, the protein that gives structure to your skin, tendons, ligaments, and blood vessels. It serves as a required helper molecule for two enzymes that modify collagen’s building blocks, making the protein stable enough to hold tissue together. Without enough vitamin C, collagen production breaks down, which is exactly what happens in scurvy.
Beyond collagen, ascorbic acid acts as a powerful antioxidant, neutralizing unstable molecules that can damage cells. It also helps your body absorb iron from plant-based foods, supports immune function, and plays a role in producing certain brain signaling chemicals. Because it’s water-soluble, your body doesn’t store large reserves. You need a steady intake to maintain healthy levels.
Best Food Sources
Many people associate vitamin C with oranges, but several foods contain significantly more per serving. A cup of frozen orange juice concentrate (undiluted) delivers about 379 mg. Black currants provide roughly 203 mg per cup. A cup of sliced kiwifruit gives you 167 mg, and a cup of canned tomato juice provides about 170 mg.
Other strong sources include:
- Broccoli (frozen, raw): 88 mg per cup
- Brussels sprouts (raw): 75 mg per cup
- Papaya: 88 mg per cup
- Grapefruit: 85 mg per cup of sections
- Lychees: 136 mg per cup
Because heat breaks down vitamin C, raw or minimally cooked fruits and vegetables retain the most. Steaming is gentler than boiling, and shorter cooking times preserve more of the nutrient.
How Much You Need
The recommended daily amount varies by age and sex. Adult men need 90 mg per day, and adult women need 75 mg. During pregnancy the target rises to 85 mg, and during breastfeeding it increases to 120 mg. Smokers need 35 mg more than nonsmokers because tobacco smoke increases oxidative stress and depletes vitamin C faster.
For children, requirements are lower: 15 mg for ages 1 to 3, 25 mg for ages 4 to 8, and 45 mg for ages 9 to 13. Teenagers need 65 to 75 mg depending on sex.
Deficiency and Scurvy
Blood levels of ascorbic acid below 0.2 mg/dL are considered deficient. Scurvy, the most severe form of deficiency, generally develops when levels drop below 0.1 mg/dL. Symptoms include fatigue, swollen and bleeding gums, easy bruising, slow wound healing, and joint pain. These all trace back to the body’s inability to produce healthy collagen without vitamin C.
A level above 0.6 mg/dL effectively rules out scurvy. Most people eating a varied diet with fruits and vegetables stay well above this threshold. Deficiency is more common in people with very restricted diets, heavy alcohol use, or conditions that impair nutrient absorption.
Upper Limits and Kidney Stone Risk
The tolerable upper intake level for ascorbic acid is 2,000 mg per day. Going beyond this doesn’t offer additional benefits and raises the risk of digestive problems like nausea, diarrhea, and stomach cramps.
A more serious concern with high-dose supplementation is kidney stones. Your body converts some ascorbic acid into oxalate, a compound that can crystallize in the kidneys. Research has shown that supplementation can increase oxalate absorption from food by about 31% and boost the body’s own oxalate production by roughly 39%. For people already prone to kidney stones, this is a meaningful increase in risk. If you have a history of calcium oxalate stones, keeping your vitamin C intake closer to the recommended daily amount rather than taking large supplements is the safer approach.