by Jack Norris, RD • Last updated: February 2014
|Table 1. Zinc Dietary Reference Intake (mg)4|
|0 - 6 mos||2||2|
|7 - 12 mos||3||3|
|1 - 3 yrs||3||3|
|4 - 8 yrs||5||5|
|9 - 13 yrs||8||8|
|14 - 18 yrs||11||9||13||14|
Zinc is not found in large amounts in plant foods, but as far as can be detected, vegetarians have similar zinc status to non-vegetarians (6). The best, common plant sources of zinc are legumes, nuts, seeds, and oatmeal. Table 2 shows the zinc content of selected plant foods.
Phytates, which are commonly found in plant foods, can reduce zinc absorption, and some researchers have suggested that this increases the zinc needs of vegetarians by up to 50% (5).
Symptoms of zinc deficiency include poor growth and delayed sexual maturation in children, poor wound healing, hair loss, impaired immune function, and dermatitis (especially around body orifices) (1).
The Cochrane Collaboration, a well-respected group, published a 2013 meta-analysis that concluded that zinc supplements can reduce the risk of developing the common cold, although they did not recommend an amount to take. They also determined that upon developing a cold, a zinc supplement of 75 mg per day would reduce the length of a cold by an average of one day (10).
Despite the lower absorption from plant foods, a 2013 meta-analysis showed vegans to have only a slightly lower serum zinc level than non-vegetarians, a difference of 1.17 ± 0.45 µmol/l (6). For vegetarians in developed countries, the difference was even smaller at .76 ± .27 µmol/l. Absolute values for serum zinc were not given in the analysis. Average serum zinc levels are from 10 to 15 µmol/l (7), 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 (8).
Protein increases zinc absorption. Because of this, foods high in protein and zinc, such as legumes and nuts, are good choices (2). The leavening of bread (most bread is leavened) and fermenting of soyfoods (tempeh and miso) also enhances zinc absorption (2).
A modest zinc supplement of 50 to 100% of the RDA should be safe for those who are concerned or having symptoms of zinc deficiency. The Tolerable Upper Intake Level for adults is 40 mg.
Zinc gluconate and zinc citrate are two forms that are well-absorbed. Some people do not absorb zinc oxide (9). There is evidence, though weak, that zinc picolinate is also absorbed well (11). Zinc gluconate may have the lowest levels of cadmium (12).
|Table 2. Zinc in Plant Foods3|
|Tofu||firm, raw||1/2 cup||2.0|
|Garbanzo beans||boiled||1/2 cup||1.3|
|Pinto beans||boiled||1/2 cup||0.8|
|Kidney beans||boiled||1/2 cup||1.0|
|Peanut butter||2 tbsp||0.9|
|Sunflower seeds||roasted||1/4 cup||1.7|
|Corn||yellow, boiled||1 cup||0.9|
|Cashews||dry roasted||1/4 cup||1.9|
|Chia seeds||dried||1 oz||1.0|
|Broccoli||boiled, chopped||1/2 cup||0.4|
3. USDA National Nutrient Database for Standard Reference. (Link)
4. Dietary Supplement Fact Sheet: Zinc. Office of Dietary Supplements. National Institutes of Health. Accessed 12/15/2010. (Link)
5. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc (2001) Food and Nutrition Board, Institute of Medicine. Accessed 12/28/2010. (Link)
6. 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
7. Dietary reference intakes: the essential guide to nutrient requirements. National Academy of Sciences. 2006 • link
8. Dietary Supplement Fact Sheet: Zinc. Office of Dietary Supplements. National Institutes of Health. Last reviewed: June 05, 2013 • link
9. 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
10. Singh M, Das RR. Zinc for the common cold. Cochrane Database Syst Rev. 2013 Jun 18;6:CD001364. • link
11. Barrie SA, Wright JV, Pizzorno JE, Kutter E, Barron PC. Comparative absorption of zinc picolinate, zinc citrate and zinc gluconate in humans. Agents Actions. 1987 Jun;21(1-2):223-8. (Abstract only.) • link
12. Krone CA, Wyse EJ, Ely JT. Cadmium in zinc-containing mineral supplements. Int J Food Sci Nutr. 2001 Jul;52(4):379-82. • link