Meta-Analysis of Zinc Status in Vegetarians

A few weeks ago, a meta-analysis of the zinc status of vegetarians was published (1). They only measured relative values of serum zinc and found that vegans had a slightly lower serum zinc level than non-vegetarians, a difference of 1.17 ± 0.45 µmol/l. For vegetarians in developed countries, the difference was even smaller at .76 ± .27 µmol/l.

Average serum zinc levels are around 20 µmol/l with a range of about 9 to 30 µmol/l (2), so it’s doubtful that the differences are meaningful. One caveat is that serum zinc levels are not necessarily indicative of the zinc levels in cells (3).

For full disclosure, I don’t rely only on my diet for zinc, I take a supplement and am under the strong impression that it helps prevent me from catching colds. I am, however, skeptical that the average vegan needs to supplement with zinc.

I have updated VeganHealth.org’s article Zinc with this information.

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References

1. Foster M, Chu A, Petocz P, Samman S. Effect of vegetarian diets on zinc status: a systematic review and meta-analysis of studies in humans. J Sci Food Agric. 2013 Apr 17. | link

2. Ghasemi A, Zahediasl S, Hosseini-Esfahani F, Azizi F. Reference values for serum zinc concentration and prevalence of zinc deficiency in adult Iranian subjects. Biol Trace Elem Res. 2012 Dec;149(3):307-14. (Abstract only) | link

3. Dietary Supplement Fact Sheet: Zinc. Office of Dietary Supplements. National Institutes of Health. Last reviewed: June 05, 2013 | link

16 Responses to “Meta-Analysis of Zinc Status in Vegetarians”

  1. Arcadio Says:

    Thanks! (The previous version of the zinc article on VeganHealth used to say that too much zinc can inhibit copper absorption. Is that still acurate?)

  2. Jack Norris RD Says:

    Arcadio,

    It is still true, but I removed it because if anything vegans get too much copper so I figured I shouldn’t leave that in there scaring people away from zinc because of fears of copper deficiency. It takes 50 mg of zinc per day to inhibit copper absorption (according to Linus Pauling Institute) and I’m not suggesting people take anywhere near that much.

    http://lpi.oregonstate.edu/infocenter/minerals/zinc/

  3. Dan Says:

    I am very skeptical that zinc prevents colds. Both a Cochrane review and a well done randomized trial showed zero effect on duration or frequency of the common cold (upper respiratory tract infections, URTI).

    Everyone has their own anecdotes. The plural of anecdotes does not equal data. My own anecdote is that cutting down on carb intake has reduced the colds I experience from 2-3 per winter to zero in the past two years. I’ve heard this repeated numerous times on the internet, and it makes some sense, as bathing your white blood cells in insulin and glucose makes them sluggish and torpid. Certainly diabetics are at higher risk of infections and diabetes is a disease of carbohydrate intolerance. Still, while it works for me, I would need to see proof in an RCT before recommending this approach to others strictly for cold prevention.

  4. Jack Norris RD Says:

    Dan,

    I agree with you that for people with already optimal zinc status, zinc probably does not prevent or help alleviate colds. But my suspicion was that until I started supplementing, I didn’t have optimal zinc status. In any case, since I started supplementing I have experienced my best period of cold-free living that I can remember, during which time I’ve been around plenty of people with colds themselves and have often not gotten enough sleep. I am aware that it could be a coincidence.

  5. Dan Says:

    Jack,

    Zinc … Yet another vitamin to supplement with (in order to defeat/prevent colds). Although I realize you are not broadly recommending zinc.

    I don’t know where it ends. I consume already 4 supplements. It would be nice to get all these micronutrients from functional foods.

    How does one find out if one is zinc deficient or not? In your view, is it worth testing if one isn’t having a lot of colds?

    This issue will get more significant as vegans age, since colds can lead to pneumonia, and respiratory tract infections are a leading cause of death in the US and worldwide. Osler used to call pneumonia the old man’s best friend, since it so frequently carried him off to his grave. In those days, it wasn’t fun to be old.

    Any down side to zinc supplementation, other than the cost and inconvenience? What made you start in the first place?

  6. Jack Norris RD Says:

    Dan,

    If a vegan (or near vegan) gets a lot of colds, then I would suggest trying a mild zinc supplement of 50-100% of the RDA and see if that helps.

    I was already taking a calcium supplement with some zinc (and magnesium) in it, but I went a couple weeks where I felt a cold coming on so I doubled the supplement to get more zinc and then that feeling went away. In the 2.5 years since that time, I have only had 1 mild cold that last about 48 hours. I take at least 7.5 mg of zinc per day.

    I don’t know of any proven down sides to this amount of zinc.

  7. Dan Says:

    Jack,

    Would you say there is a syndrome of impaired immunity associated with subclinical zinc deficiency among vegans?

  8. Jack Norris RD Says:

    Dan,

    > Would you say there is a syndrome of impaired immunity associated with subclinical zinc deficiency among vegans?

    I would not say that. My one anecdote of myself is not enough to suggest a syndrome.

  9. Idan Says:

    Hi jack i just found this article – in it it seems like Cadmium is directly related to plant food consumption years which is not a good thing.

    http://www.researchgate.net/publication/6647587_Cadmium_blood_concentrations_in_relation_to_nutrition

    It has also a little relevance to the post and also is interesting by itself – I’m not sure if there is more research on this but it would be good to know how much Cadmium in our food.

    What do you think about this jack ?

  10. Jack Norris RD Says:

    Idan,

    I had not seen that study previously. I hope they’re right that the antioxidant status of vegetarians would counteract the effect of higher cadmium levels. I wonder if this is true in other countries.

  11. Daniel Says:

    I listened to that calcium supplements reduce zinc absorption.

    I would like to know if you think it’s a bad idea to eat zinc-fortified cereals with calcium-fortified soya drink.

  12. Jack Norris RD Says:

    Daniel,

    > I would like to know if you think it’s a bad idea to eat zinc-fortified cereals with calcium-fortified soya drink.

    I don’t think you need to worry about this – it’s much higher calcium amounts that matter.

  13. Andreas Says:

    “One caveat is that serum zinc levels are not necessarily indicative of the zinc levels in cells.” – Agreed. Especially when someone is free of hyperlipidemia.

    It would be excellent if these studies indicated the Vitamin D/B12 deficient subjects for the purpose of removing bias. According to the science, Calcitriol is required for the absorption of the certain minerals, including zinc, in the small intestine.and the reabsorption of minerals in the renal tubule. So, low Calcitriol(active Vitamin D) levels leads to less absorption of minerals in the small intestine and greator excretion of minerals to the urine.

    Effect of Vitamin D on the Utilization of Zinc…
    http://jn.nutrition.org/content/75/2/222.full.pdf

    These videos might be of interest…
    http://www.youtube.com/watch?v=RFsnDMkRrLc
    http://www.youtube.com/watch?&v=bb3kgbUCUuI

    I prefer taking a Vitashine Vegan Vitamin D3 supplement in the winter when I feel my levels are lower for the purpose of keeping my immune system flu proof.

  14. Kate Scott Says:

    The cadmium issue is a worry – especially in New Zealand where I live. See this recent news item: http://www.3news.co.nz/The-dangers-of-Cadmium/tabid/367/articleID/293891/Default.aspx

  15. Jack Norris RD Says:

    Kate,

    That’s unfortunate. Dr. Greger just mentioned tuna as the highest source of cadmium in this video here:

    http://nutritionfacts.org/video/reducing-radiation-damage-with-ginger-and-lemon-balm/

    But I think they were only measuring animal products (not sure about that). If so, then one would think that pesco-vegetarians would really be the worst group off and yet their rates of disease are generally pretty low. Of course, I haven’t seen comparisons between the blood levels of cadmium in pesco-vegetarians and New Zealand vegetarians to know if they are much higher in the NZ vegetarians.

  16. Kate Scott Says:

    My understanding is that although cadmium is high in some seafood (like tuna and oysters), when it is bound to protein it is much less bio-available. It is the unbound form (in grains and veges) that is more available. So I think it is a concern for vegans and vegetarians, and it is relevant to the topic of this thread because the effects of cadmium are greater in those with lower levels of zinc, iron and calcium. Studies in New Zealand show that its highest concentrations are in breads, root veges and leafy greens (and fish). This bothers me because I drink vege juices from these veges daily. However, the Slovakian study posted by Idan above offers some hope that the antioxidants from the veges themselves counteract the effects of dadmium. But another reason to perhaps take a low dose zinc supplement.

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