Zinc Supplements and the Common Cold

In June of 2013, the Cochrane Collaboration updated their meta-analysis of double-blinded, placebo-controlled randomized controlled trials testing whether zinc is useful in treating or preventing the common cold (1).

Their analysis included 16 trials for treating colds, with a total of 1,387 participants. Intake of zinc was associated with a significant reduction in the duration of the cold, reducing it by about one day. It did not show a benefit in reducing the severity of the symptoms.

Of the 16 trials, 11 showed benefit for zinc, while the others did not. The authors reported that trials showing no benefit have been criticized for using too little zinc or a form that is not bioavailable. (Zinc gluconate is a good choice for bioavailability; more on that in a future post.)

The analysis also included two preventive trials with a total of 394 participants. Both studies found a statistically significant benefit from zinc supplementation with the combined incidence of developing a cold reduced by 36% (0.64, 0.47-0.88).

As for how zinc helps treat or prevent colds, the authors had a few explanations. Zinc ions have an affinity for the receptor sites where the cold virus (rhinovirus) attaches to the nasal passages. It can bind both to the virus and to the nasal passages, thus blocking the ability of the virus to attach. Zinc might also prevent the formation of virus proteins, stabilize cell membranes, prevent histamine release, and inhibit prostaglandin metabolism.

The authors suggest treating a cold with 75 mg of zinc per day. They did not give an amount for preventing colds.

I have written before about the idea that some vegans might benefit from a zinc supplement for immune function and wound healing (see the VeganHealth.org article Zinc). A side benefit of zinc supplementation is that it can prevent cadmium absorption (see the Zinc and Alzheimer’s Disease section of the VeganHealth.org article Cadmium).

Personally, I have taken zinc for a number of years now and I have never had so few colds; those I’ve had have lasted less than a day rather than the usual week. So, whether it is a placebo or a coincidence, I continue to take zinc religiously, in two daily doses of 3.75 mg (as part of a Trader Joe’s calcium, magnesium, and zinc supplement).

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References

1. Singh M, Das RR. Zinc for the common cold. Cochrane Database Syst Rev. 2013 Jun 18;6:CD001364. | link

17 Responses to “Zinc Supplements and the Common Cold”

  1. Dan Says:

    Me too – very few colds in the past 3 years. But I don’t take zinc. So I must be an opposing data point. Since I am already loading up with enough supplements as it is, I am leary of adding another one to the mix. There are no long-term safety trials in large samples for zinc supplementation, although it’s been looked at as part of a larger antioxidant cocktail in some trials (which is not helpful for understanding zinc’s effects in isolation). I take the precautionary principle on this one, since I’ve learned my lesson from vitamin A, beta carotene, vitamin E, magnesium, folic acid (controversial), vitamin C, glucosamine, etc….

  2. Jack Norris RD Says:

    My wife is data point two on my side, but she has also not been traveling nearly as much for work in the past few months which could explain her not getting colds. Anyone else? With a few more data points, we could publish our own meta-analysis!

    Just kidding, of course. This is by far the weakest form of evidence, though I did correspond with a raw foodist awhile back who said that anecdotal reports are the only thing he cares about due to the methodological problems with nutrition research. I hadn’t heard that before!

  3. Dan Says:

    It’s a blend. Each person is an anecdote, a pre-post study. However, I use population-based statistics to guide treatment, then I check in with the “anecdote” to measure how they are doing.

    I am also not quite sure that your dose of zinc (6.5 mg per day) is enough to prevent colds, compared with some of the doses used in this meta-analysis.

    Asked four more patients today to buy your book.

  4. Jack Norris RD Says:

    > I am also not quite sure that your dose of zinc (6.5 mg per day) is enough to prevent colds, compared with some of the doses used in this meta-analysis.

    I would think that in terms of cold prevention, the reason zinc helps me is simply strengthening my immune system due to the lower zinc intake/absorption on plant-based diets and possibly a greater need for myself. I agree that it probably wouldn’t be enough to have an affect on rhinovirus attachment in the nasal passages, though I’m not sure.

    Thanks for recommending my book!

  5. Dan Says:

    >>due to the lower zinc intake/absorption on plant-based diets

    I thought the main meta-analysis in this area only showed a slightly lower zinc level across trials, but I could be wrong. Is plant-based zinc less absorbable?

    When I checked my zinc intake a while back, I was exceeding the recommended intake by a bit, but I have since cut back a fair amount on nuts and seeds, and I am possibly now below the recommended level. However, I am reluctant to take a calcium-magnesium-zinc supplement as there are some data that magnesium supplementation may be harmful – a large randomized trial in CAD patients about 15 years ago strongly showed this.

  6. Jack Norris RD Says:

    Dan,

    > Is plant-based zinc less absorbable?

    Theoretically, yes, as phytate binds zinc.

    Serum zinc levels are not necessarily a good representation of zinc status, unfortunately.

  7. Cobie deLespinasse Says:

    I think you mean 36%, not 46%. That 36% makes zinc sound good, maybe I’ll try adding zinc.

  8. Jack Norris RD Says:

    Thanks, Cobie!

  9. Cobie deLespinasse Says:

    Just by coincidence, this evening I heard one of my housemates telling someone that he hasn’t gotten minor illnesses as much since he started drinking warm water on a regular basis. He says he doesn’t know of any studies about it. I don’t know what it means, that’s just what he says.

  10. Dan Says:

    I am beginning to get the impression that multiple micronutrient deficiencies may occur in a vegan diet (zinc, yes, but also calcium, iodine, B12, DHA, and perhaps selenium and vitamin D — though the latter seems to be deficient in many non-vegans too). I always find it a remarkable paradox that vegans do so much better on major health metrics (cardiovascular, cancer, bone health, etc), yet these micronutrient issues persist.

    (In addition, there is K2, taurine, creatine, L-carnitine and choline; all of which tend to be low in vegan diets. There is the issue of other trace metals like iron.)

    I don’t know how to reconcile the paradox, unless all the vegans in the studies to date have been taking supplements (hard to believe). Or else these micronutrients are just not relevant to health (hard to believe), at least in comparison with the health benefits of eliminating animal fat/protein/cholesterol. Another possibility is selection bias and residual confounding, yet this does not explain the dramatic results produced by Ornish and Esselstyn.

  11. Cobie deLespinasse Says:

    You mention supplements from Trader Joe’s. I’ve sometimes wondered how much difference it makes for animals whether the supplements we take are vegan? I don’t know if Trader Joe’s supplements are vegan. Their prices are probably good at Trader Joe’s. Certainly, I’ve heard people say that they do not want to go vegan because they don’t want to pay to take supplements, so maybe getting supplements at as low cost as possible could encourage people to go vegan.

  12. Jack Norris RD Says:

    Cobie,

    Since making my zinc posts, it occurred to me to check out which type of zinc is in my Trader Joe’s supplement and, unfortunately, it’s zinc oxide, the form that it appears a small percentage of people (about 20%) don’t absorb well. Given my experience with it, I either seem to be in the 80% who absorb it or my sense that zinc helps me is mistaken.

    As for being vegan, unless an ingredient in a supplement is clearly not vegan, I don’t worry about it. And I don’t expect people in the general public to worry that much when trying to be vegan. If people just stopped eating obvious animal products but didn’t care about how vegan their supplements were, I’d be very happy.

  13. Brandon Becker Says:

    This video shows the results of a study (linked below the video) that said that average vegans are only deficient in calcium, iodine, and B12 whereas average omnivores are deficient in calcium, fiber, folate, iodine, magnesium, vitamin c, and vitamin e: http://nutritionfacts.org/video/omnivore-vs-vegan-nutrient-deficiencies-2/

    It’s not hard to get enough calcium on a vegan diet if you eat lots of dark green leafy vegetables and/or drink fortified plant milks. Seaweed easily provides all the iodine anyone needs (I take a supplement because I don’t eat it often) and it can also be found in plants grown in soil with iodine stores. B12 is the only real problem for vegans and that is easily solved with fortified foods or a supplement.

    I’m not convinced that DHA is really needed in a supplement if you are getting enough ALA but I take it occasionally just in case (I get bruises if I take it on a regular basis and it takes a lot for me to bruise otherwise).

    Selenium should only be a problem for northern Europeans (due to their soil content) and that is solved with Brazil nut consumption. I used to worry about zinc but my diet log on peacounter.com shows that I’m meeting or exceeding the RDA, so if I was going to supplement, it would find a low dose.

    Someone is likely to encounter deficiencies if they restrict certain foods, don’t eat enough food in general, or don’t eat a wide variety of foods.

  14. Dan Says:

    Brandon,
    I am not concerned with B12 as I supplement. I am more concerned about other B vitamins (pyridoxine, pantothenic acid, niacin, riboflavin) as well as some missing amino acids (taurine, L-carnitine, creatine). I have no problem supplementing with iodine. My diet is somewhat restrictive in that I do not consume a large amount of grain, unlike many vegans, nor do I eat copious quantities of fruit (I do eat limited quantities). I also eat a lot of cruciferous vegetables and legumes. My diet could be characterized as being “Eco-Atkins” but without a lot of vegetable oils or avocados. I eat fairly similar foods every day.

  15. Brandon Becker Says:

    Have you seen Dr Fuhrman’s multivitamins?:
    http://www.drfuhrman.com/shop/multi_details.aspx

    If I wasn’t able to meet everything from my diet or didn’t want to buy supplements separately, I’d probably take these. I wish they didn’t have manganese in them, though, and would have a higher level of methylcobalamin B12 or source it from cyanocobalamin instead.

  16. newt Says:

    Jack, are you sure that the zinc amount you wrote above is correct? Your supplement only has a total of 6.5 mg of zinc in two pills? The bottle of Trader Joe’s Magnesium, zinc, calcium that I’ve seen has 15mg of zinc in two pills.

  17. Jack Norris RD Says:

    newt,

    Good catch. I meant to say 3.75 mg.

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