Vitamin C
Today
3-day window. Water-soluble and not stored, so a short run of days is the signal.
What it is
Vitamin C is what your body uses to build collagen — the protein holding skin, blood vessels, and gums together — and it makes iron from plant foods far easier to absorb. Your body doesn't store it, so you need some most days. The good news is it's easy to get: one red pepper or one kiwi covers a full day. It does not prevent colds, despite the reputation, though it does shorten them slightly.
Reference intake
Your daily target, personalised to your age and sex.
- RDA
- 90 mgmale_19_plus
- Upper limit
- 2000 mgapplies to total
Smokers require an additional 35 mg/day above the RDA. The UL is set by gastrointestinal tolerance, not systemic toxicity.
What the evidence says
Wording reflects how strong the evidence actually is.
Prevents scurvy
Substantially increases non-heme iron absorption
May shortens the duration of the common cold
Has been associated with: prevents the common cold
Deficiency
scurvy
Roughly 7% of the US population has serum levels indicating deficiency (NHANES), concentrated among smokers and people with low fruit and vegetable intake. Frank scurvy is rare but persistently under-diagnosed in people with restrictive diets, alcohol dependence, or severe mental illness.
Early signs
- fatigue and lethargy
- irritability
- muscle and joint aching
- easy bruising
- slow wound healing
Higher risk
- smokers (need an additional 35 mg/day due to oxidative turnover)
- people with very limited dietary variety
- alcohol dependence
- people on dialysis
- severe malabsorptive conditions
- infants fed exclusively on boiled or evaporated milk
Excess
No adverse effects from food sources. Renal excretion handles any dietary excess.
From supplements
- diarrhea and abdominal cramping
- nausea
- increased urinary oxalate, relevant to kidney stone formers
- false readings on some blood glucose meters
At extreme doses
Doses above roughly 1,000 mg/day may raise oxalate stone risk in susceptible people. In hereditary hemochromatosis, high doses can worsen iron overload by increasing absorption.
Absorption
70–90% at typical intakes; falls below 50% above 1,000 mg in a single dose
Helps absorption
- splitting intake across the day
- consuming from whole foods, where it arrives with flavonoids
Hinders absorption
- smoking (increases metabolic turnover rather than blocking absorption)
- heat — vitamin C is among the most cooking-labile nutrients
- prolonged storage and exposure to air
- boiling, which leaches it into the water
Top sources
Per 100 g, in mg. FoodData Central IDs are resolved by the importer, not written by hand.
- 228 mg
Guava
55 g (1 fruit)
- 128 mg
Bell pepper, red, raw
119 g (1 medium)
- 93 mg
Kiwifruit
69 g (1 fruit)
- 89 mg
Broccoli, raw
91 g (1 cup)
- 59 mg
Strawberries
152 g (1 cup)
- 53 mg
Orange
131 g (1 medium)
Ranking these by what you already eat needs the real log — see docs/STATUS.md.
Sources
Last reviewed 2026-08-11