You’re Taking Enough Vitamin C to Prevent Scurvy. That’s About It.

The recommended daily intake for vitamin C is 90 milligrams for men and 75mg for women. That number was set to prevent scurvy, a disease that killed roughly two million sailors between 1500 and 1800.

Scurvy prevention is a low bar. The research on immune function, collagen production, and antioxidant protection starts at two to three times that dose.

How the RDA got so conservative

The current recommended dietary allowance was established by the Institute of Medicine in 2000. They set it at the level needed to maintain near-maximal neutrophil vitamin C concentration with minimal urinary excretion. In plain language: just enough to saturate one type of immune cell without “wasting” any in urine.

The NIH Office of Dietary Supplements notes that this amount prevents scurvy and provides modest antioxidant protection, but acknowledges that higher intakes follow different pharmacokinetics.

The Linus Pauling Institute at Oregon State University, which has spent decades studying vitamin C specifically, recommends 400mg per day for healthy adults. Not 90. Not the megadoses Linus Pauling himself promoted (which were arguably too high). Four hundred milligrams, based on dose-response data for disease prevention and tissue saturation across the accumulated literature.

What vitamin C does beyond preventing scurvy

Vitamin C is a cofactor for at least eight enzymatic reactions. The most important is collagen synthesis. Collagen is the most abundant protein in your body, about 30% of total protein. It’s the structural framework of skin, joints, blood vessels, bones, tendons, and gut lining. Without adequate vitamin C, collagen production slows. That is literally what scurvy is: collagen falling apart because the body can’t make enough new collagen to replace it.

At intakes above scurvy-prevention levels, vitamin C supports immune function by enhancing neutrophil motility, lymphocyte proliferation, and antibody production. A 2017 review in the journal Nutrients compiled evidence from multiple trials showing that regular vitamin C supplementation at 200mg or more reduced the duration of common colds by 8% in adults and 14% in children.

It also helps iron absorption, converting non-heme iron (the form in plants and supplements) from its ferric to ferrous state, which your gut can actually absorb. One study found that 100mg of vitamin C taken with a meal increased non-heme iron absorption by up to 67%.

And it regenerates vitamin E. After vitamin E neutralises a free radical, it becomes oxidised and inactive. Vitamin C donates an electron to recycle it back to active form. Without C, your vitamin E depletes faster. Nutrients rarely work in isolation.

The dose-response curve isn’t linear

Your body absorbs vitamin C through active transport in the small intestine. At low doses (under 200mg), absorption is nearly 100%. At 500mg, it drops to about 75%. At 1,000mg, roughly 50%. Higher still, and the excess draws water into the intestine, which is why megadoses cause diarrhea.

Plasma levels plateau around 200-400mg per day. Beyond that, blood concentrations don’t rise much, but tissue levels may continue to build. This is why the Linus Pauling Institute’s 400mg recommendation makes pharmacological sense: it saturates plasma and provides meaningful tissue reserves without excessive waste.

During illness or physical stress, your body burns through vitamin C faster. White blood cells actively concentrate vitamin C at 50-100 times plasma levels during infection. A sick person’s vitamin C requirements are genuinely higher than a healthy person’s. This is why supplementation during illness (500-1,000mg/day) has more evidence behind it than daily megadosing while healthy.

Your body can’t store it

Vitamin C is water-soluble. Unlike fat-soluble vitamins (A, D, E, K) that accumulate in tissue, excess vitamin C is filtered by the kidneys and excreted within hours. The body maintains a pool of roughly 1,500mg, with a half-life of 10-20 days.

This means you need a daily supply. Miss a few days and the pool starts to deplete. It also means split doses (250mg twice a day rather than 500mg at once) maintain more stable blood levels, since absorption is better at lower individual doses.

Smokers need more. The NIH recommends smokers add 35mg/day to the baseline because oxidative stress from smoking depletes vitamin C faster. Heavy exercise, chronic stress, and alcohol have a similar effect.

Ascorbic acid vs the expensive alternatives

Plain ascorbic acid is the most studied form and works fine for most people. Cheap, well-absorbed, decades of clinical data.

Buffered forms like calcium ascorbate or sodium ascorbate are gentler on the stomach at higher doses. They’re not better absorbed, just easier on the gut if acid reflux is an issue for you.

Liposomal vitamin C wraps ascorbic acid in phospholipid bubbles, theoretically improving absorption. A 2016 study in Nutrition and Metabolic Insights found liposomal delivery produced higher circulating levels than standard ascorbic acid at the same dose. The effect is real but modest, and liposomal products cost 5-10x more per milligram.

“Vitamin C with rose hips” or “natural vitamin C from acerola” are mostly marketing angles. The vitamin C molecule is identical regardless of source. Rose hips contain some bioflavonoids, but the amounts in a supplement capsule are typically too small to matter.

Get the dose right

For general health: 200-500mg per day, ideally split into two doses. This saturates plasma, supports collagen production, keeps your immune cells resourced, and stays well within safe limits.

During illness: 500-1,000mg per day until symptoms resolve.

The upper limit set by the IOM is 2,000mg/day, which isn’t a danger threshold. It’s the point at which GI side effects (diarrhea, cramping) become common. True vitamin C toxicity from supplements is essentially unheard of in the medical literature.

From food: one red bell pepper has 190mg. A cup of strawberries has 90mg. A kiwi has 70mg. A medium orange has 70mg. Most people eating a reasonable amount of fruit and vegetables get 100-200mg from diet alone. Supplementing 200-300mg on top of that puts you in the optimal range without overthinking anything.

For the full breakdown of the form and dose in Fireblood, see our vitamin C ingredient page.

Fireblood includes 500mg of vitamin C per scoop, alongside vitamin D, magnesium, and 36 other nutrients. See the full formula.