Because many vegetarians and vegans eat a high-oxalate diet, I have been interested to see if a prospective study might find a higher risk of kidney stones.

A recently released report from EPIC-Oxford measured the risk of being hospitalized for a kidney stone over the course of five years for people in various diet groups (1). Vegetarians (including vegans) had a 31% lower risk (.69, .48–0.98) as compared to high meat-eaters.

The other diet groups were:

Moderate meat-eaters, 50–99 g of meat per day – 0.80 (.57–1.11)
Low meat-eaters, < 50 g of meat per day – 0.52 (.35–0.80)
Fish-eaters – .73 (.48–1.11)

Oxalate intake was not measured.

I have updated Oxalate at VeganHealth.org with this info.

The authors also found a correlation between zinc intake and kidney stones. However, this finding barely reached statistical significance and the rate of kidney stones were very low in this population (.6% over five years). Kidney stones were not a common enough side effect in the recent Cochrane Database Analysis of clinical trials on zinc to be mentioned in their report.

Considering all of this, I am not worried that a modest zinc supplement will lead to a kidney stone.

References

1. Turney BW, Appleby PN, Reynard JM, Noble JG, Key TJ, Allen NE. Diet and risk of kidney stones in the Oxford cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC). Eur J Epidemiol. 2014 Apr 22. [Epub ahead of print] | link

A 2014 study from Switzerland compared the absorption from various forms of zinc supplements (1). Measuring zinc absorption in 15 healthy volunteers, they found the following median absorption rates:

zinc citrate – 61% (range: 57–71)
zinc gluconate – 61% (range: 51–72)
zinc oxide – 50% (range: 41–58)

The lower absorption from zinc oxide was almost entirely due to three participants who absorbed much lower amounts, with two absorbing almost none.

The authors reviewed other studies which indicated that zinc sulfate and zinc acetate might also be absorbed well.

Interestingly, they noted that none of the study subjects were vegan. They didn’t explain why they pointed this out, but it’s good to know that vegans are on their radar.

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References

1. Wegmüller R, Tay F, Zeder C, Brnic M, Hurrell RF. Zinc absorption by young adults from supplemental zinc citrate is comparable with that from zinc gluconate and higher than from zinc oxide. J Nutr. 2014 Feb;144(2):132-6. | link

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

After posting the article Cadmium Levels in Vegans, Zinc Supplements and Alzheimer’s Disease, Ginny Messina let me know that there is a concern about cadmium contamination of zinc supplements.

I researched the issue and added the following section to VeganHealth.org’s article Cadmium:

In 2001, Krone et al tested six zinc supplements from Seattle area health food stores to see if they contained cadmium (1). According to the authors, “Because the chemical properties of [zinc] and cadmium (Cd) are so similar, these two elements invariably occur together in nature.”

They found that the single zinc supplements had very low levels of cadmium whereas the multi-mineral supplements had enough that taking the RDA of zinc would provide up to 2 µg of cadmium (20% of the daily limit recommended by the US Federal Drug Administration (FDA)). It also happens that three of the supplements with low levels of cadmium were in the form of zinc gluconate whereas none of the multi-mineral preparations were the gluconate form. So, it could be that zinc gluconate is unlikely to have much cadmium or that single zinc supplements are unlikely.

According to their website, the supplement manufacturer Kirkman, from Oregon, does a rigorous job testing their supplements for contamination of cadmium and other impurities (more info). They also have an article on their site, Cadmium: A Serious Heavy Metal and Topic. They ship outside the United States.

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References

1. Krone CA, Wyse EJ, Ely JT. Cadmium in zinc-containing mineral supplements. Int J Food Sci Nutr. 2001 Jul;52(4):379-82. | link

Wow – my last real post was on June 27th. But I have not fallen off the face of the earth – rather, it was right around that time that a reader brought my attention to a disconcerting study from 2006 which showed vegans in the Slovak Republic to have significantly higher cadmium levels than other diets groups. This study set me off on quite a journey that led to examining the role of zinc in Alzheimer’s Disease, of all things, and ended up strengthening my suspicions that vegans might benefit from zinc supplementation. In this case, not only because vegans can sometimes have low zinc intakes, but also to help reduce any problem caused by higher cadmium and copper intakes.

I have added this information to VeganHealth.org in an article on Cadmium. The article is too long to reproduce here, so I hope you will click through and give it a read.

I was disappointed that I had not previously heard of the study from the Slovak Republic, but these days I get notifications for any studies on vegetarians or vegans that get added to PubMed, so hopefully none will eascape my notice again.

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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

Just added two tables to the VeganHealth.org page on zinc. Table 1 lists the DRIs and Table 2 lists plant foods high in zinc. Link.