Question explored with the scientific record
Vitamin c
The short version: vitamin C is cheap and low-risk, but the human evidence that it fixes anything beyond a true deficiency is thin, and most of what surfaced here is about inflammation markers, not how you feel.
The strongest human data in this batch is a randomized, placebo-controlled trial of 1,000 mg/day for two months in healthy nonsmokers [1]. It lowered C-reactive protein, an inflammation marker, only in people who started with elevated CRP, about a 17% drop versus a rise on placebo [1]. People with normal CRP saw no effect [1]. That is a lab value, not a symptom or a survival outcome, and it is one trial.
A crossover trial in 60 asthmatic children found 0.2 g/day improved asthma control and lung function, but the benefit was much larger in younger kids with milder asthma (about 4 points on a symptom score) than older kids with more severe disease (about 1 point) [3]. That is a real clinical outcome in a small, single trial with many subgroup comparisons.
For bone health, the review is blunt: vitamin C is essential for collagen, but there is no proof it prevents osteoporosis or fractures, and only one double-blind trial exists, which bundled vitamin C with vitamin E and exercise so you cannot credit vitamin C alone [2].
| Finding | What it actually shows |
|---|---|
| CRP drop, 1,000 mg/day [1] | Lab marker only, elevated-CRP subgroup |
| Asthma control, 0.2 g/day [3] | Small single trial, effect varies by age |
| Bone/fracture protection [2] | Not proven; trials too few and confounded |
My call: worth taking if you are deficient or eat poorly, and reasonable to try for asthma symptoms in a child, but do not expect it to prevent fractures or disease, and the evidence for any specific benefit is low quality. Confidence: low.
Sources used 3
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Vitamin C treatment reduces elevated C-reactive protein
A randomized, placebo-controlled trial in healthy nonsmokers found that 2 months of 1000 mg/day vitamin C reduced C-reactive protein (CRP) only in participants with elevated baseline CRP (≥1.0 mg/L), while 800 IU/day vitamin E had no significant effect, suggesting vitamin C may …
DOI: 10.1016/j.freeradbiomed.2008.09.030 -
Is there a role for vitamin C in preventing osteoporosis and fractures? A review of the potential underlying mechanisms and current epidemiological evidence
Vitamin C may influence bone health via collagen synthesis and osteoblast/osteoclast regulation, but current evidence does not prove a causal protective effect against osteoporosis or fractures; more high-quality randomized trials of vitamin C alone are needed.
DOI: 10.1017/s0954422414000195 -
Vitamin C and asthma in children: modification of the effect by age, exposure to dampness and the severity of asthma
In a randomized crossover trial of 60 Egyptian children with asthma, vitamin C improved asthma control and FEV1 overall, with effects modified by age, baseline asthma severity, and bedroom dampness.
DOI: 10.1186/2045-7022-1-9