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Do vitamins (taken as pills) boost your immune system, and make you less likely to contract diseases such as common cold or flu?

Is there scientific evidence either way?

I tend to think that vitamin pills are mostly useless. If they were beneficial, surely doctors and health organisations would recommend them, but it doesn't appear to be the case.

However, many people feel quite strongly about vitamins and supplements, with the reasoning that "if they can't help, at least they can't hurt".

Is there is a medical consensus over this question?

  • 2
    Haha, I like the wording "is there scientific evidence either way?". Probably yes, on that type of question the problem is usually not that we don't have enough evidence, it is that we have lots of contradictory and inconclusive evidence. – rumtscho Dec 10 '15 at 19:37
  • Chicken soup and clove :D – Totoro Dec 10 '15 at 19:59
  • Nemo - Can you clarify one point, do you mean vitamins as a supplement to a poor diet? Or benefit for someone already eating healthily? – JohnP Feb 17 '16 at 20:27
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Research results are somewhat inconsistent but generally seem to be unfavorable to vitamins alone (in contrast to vitamins in combination with other things).

From "Prevention and treatment of the common cold: making sense of the evidence" (2014):

Zinc appears to be effective in reducing the number of colds per year, at least in children. (...) vitamin D and echinacea showed no evidence of benefit. Vitamin C may provide some benefit in people under physical stress (e.g., marathon runners or soldiers in subarctic environments), but no meaningful benefit has been shown for the average patient. (...) Evidence for interventions aimed at preventing and treating the common cold is frequently of poor quality, and results are inconsistent. The best evidence for the prevention of the common cold supports physical interventions (e.g., handwashing) and possibly the use of zinc supplements.

(Caution: be aware, that intranasal zinc may induce some adverse effects, i.e. anosmia syndrome.)

From "Vitamin C for preventing and treating the common cold." (2013):

The failure of vitamin C supplementation to reduce the incidence of colds in the general population indicates that routine vitamin C supplementation is not justified

From "The effect of exercise on prevention of the common cold: a meta-analysis of randomized controlled trial studies." (2015):

Dietary supplements, such as vitamin C and E, are used by many people, especially athletes. The users often believe that high dosages of supplements improve health (resistance to illness and disease) and physical performance. These assumptions are, however, generally not supported in the scientific literature.

From "Vitamin D for prevention of respiratory tract infections: A systematic review and meta-analysis" (2012):

On the basis of this study, we can conclude that vitamin D is useful in prevention of respiratory tract infections. But looking at the availability of only five clinical trials there is need of conduction of more clinical trials so that more valid conclusion can be reached.

From "Effect of vitamin D3 supplementation on upper respiratory tract infections in healthy adults: the VIDARIS randomized controlled trial." (2012):

(...) monthly administration of 100,000 IU of vitamin D did not reduce the incidence or severity of URTIs in healthy adults.

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