Supplement
Vitamin C
Essential for deficiency; the megadose cold cure is mostly myth.
Vitamin C (ascorbic acid) is an essential water-soluble vitamin required for collagen synthesis, carnitine production, and immune-cell function. We grade Vitamin C B on evidence and A- for worth-it at about $3-8 per month.
Evidence
Worth it
Typical cost: $3-8/month
What it does
Vitamin C (ascorbic acid) is an essential water-soluble vitamin required for collagen synthesis, carnitine production, and immune-cell function. Humans cannot make it, so intake must come from food or supplements; immune cells saturate at around 100 mg/day of intake.
What the research says
Prevents deficiency and supports normal immune function
Evidence: strong. Deficiency causes scurvy; repletion restores immune-cell function. This is the non-controversial core of the vitamin C case.
Slightly shortens colds when taken regularly before illness
Evidence: moderate. The Cochrane review of 29 trials (11,306 participants) found regular supplementation cut cold duration 8% in adults and 14% in children, and a 2023 meta-analysis found a 15% reduction in severe symptoms. Taking it at symptom onset showed no benefit.
Halves cold incidence in athletes and soldiers under heavy physical stress
Evidence: moderate. Subgroup analyses consistently show roughly 50% fewer colds in marathon runners, skiers, and military personnel taking vitamin C regularly; the general population sees no incidence reduction.
The deficiency case is airtight and the athlete data is consistent, but Pauling-era megadose claims collapsed under replication: no cold prevention in the general population, no benefit from starting at symptom onset, and absorption ceilings make gram doses mostly expensive urine. A solid B for what it actually does.
What the experts say
Every position links to its source. We include skeptics alongside supporters.
Linus Pauling
Historically claimed gram-dose vitamin C prevents and treats colds; later meta-analyses substantially weakened the claim.
Is it worth it?
Derived from the October 2026 worth-it model: B evidence at about $5.5 a month, targeted applicability, scored as evidence squared over the square root of cost.
Typical cost
$3-8/month
Common form, not a brand recommendation
Dosage contextestablished
RDA is 75-90 mg/day; 200-500 mg/day saturates tissues. Absorption per dose plateaus around 200-400 mg, so split larger intakes. Megadoses above 1 g add little.
Safety notes
Very safe at normal doses; the tolerable upper intake is 2,000 mg/day. Higher doses commonly cause diarrhea and GI upset. People prone to kidney stones should stay conservative, as oxalate excretion rises with dose.
Longevity Lab Report
Vitamin C news, graded when it happens.
The grade on this page stays free. The reporting goes further in the email: new studies, dose debates, and expert shifts on vitamin c, including stories that never get posted here.
Frequently asked questions
Is Vitamin C safe?
Very safe at normal doses; the tolerable upper intake is 2,000 mg/day. Higher doses commonly cause diarrhea and GI upset. People prone to kidney stones should stay conservative, as oxalate excretion rises with dose.
What is the right dose of Vitamin C?
RDA is 75-90 mg/day; 200-500 mg/day saturates tissues. Absorption per dose plateaus around 200-400 mg, so split larger intakes. Megadoses above 1 g add little.
Is Vitamin C worth taking?
We grade Vitamin C A- for worth-it at a typical cost of $3-8 per month. Derived from the October 2026 worth-it model: B evidence at about $5.5 a month, targeted applicability, scored as evidence squared over the square root of cost.
Changelog
Last updated 2026-10-17
- 2026-10-16|New DRAFT entry, batch 3.
- 2026-10-17|Applicability assigned (targeted) for the worth-it leaderboard methodology update of 2026-10-17.
- 2026-10-17|Worth-it grade derived from the October 2026 worth-it model (same gated model as the leaderboard); applicability recorded for all records.