Zinc

by Jack Norris, RD

Contents

• Essential Information
• Dietary Reference Intakes for Zinc
• Zinc Content of Plant Foods
• Additional Tips
• Zinc Deficiency
• Zinc Absorption and Status of Vegans
• Zinc and Alzheimer’s Disease
• Bibliography

Essential Information

Vegans tend to meet the RDA for zinc, but due to zinc being harder to absorb from plant foods, some vegans might need more than the RDA. If a vegan has found that while on the diet they easily catch colds, develop angular cheilitis (cracks in the corners of the mouth), diarrhea, or hair loss, then a modest zinc supplement of about 50-100% of the RDA might resolve such issues.

Dietary Reference Intakes

U.S. Dietary Reference Intakes (DRI) for Zinc
Age	DRI (mg)	Upper Limit (mg)
0–6 mos	2	4
7–12 mos	3	5
1–3	3	7
4–8	5	12
9–13	8	23
14–18 male	11	34
14-18 female	9	34
≥ 19 male	11	40
≥ 19 female	8	40
Pregnancy
14–18	12	34
19–50	11	40
Breastfeeding
14–18	13	34
19–50	12	40

Zinc Content of Plant Foods

The common plant foods highest in zinc are legumes, nuts, seeds, and oatmeal. The table below shows the zinc content of selected plant foods (USDA National Nutrient Database for Standard Reference).

Zinc in Plant Foods
Food	Preparation	Serving	mg
Oatmeal	cooked	1 cup	2.3
Tofu	firm, raw	1/2 cup	2.0
Cashews	dry roasted	1/4 cup	1.9
Sunflower seeds	roasted	1/4 cup	1.9
Garbanzo beans	boiled	1/2 cup	1.3
Lentils	boiled	1/2 cup	1.3
Peanuts	raw	1/4 cup	1.2
Almonds	whole	1/4 cup	1.1
Pecans	halves	1/4 cup	1.1
Tempeh	raw	1/2 cup	1.0
Kidney beans	boiled	1/2 cup	1.0
Peas	boiled	1/2 cup	1.0
Chia seeds	dried	1 oz	1.0
Walnuts	chopped	1/4 cup	0.9
Peanut butter		2 tbsp	0.9
Corn	yellow, boiled	1 cup	0.9
Pinto beans	boiled	1/2 cup	0.8
Pistachios		1/4 cup	0.7
Miso		1 tbsp	0.4
Broccoli	boiled, chopped	1/2 cup	0.4

Additional Tips

Fermenting soyfoods enhances zinc absorption; tempeh and miso are fermented (Messina, 2001).

Regarding supplements, zinc gluconate and zinc citrate are two form of zinc that are well-absorbed; some people don’t absorb zinc oxide (Wegmüller, 2014). There’s evidence, though weak, that zinc picolinate is also absorbed well (Barrie, 1987). Zinc gluconate may be the best choice due to lower levels of cadmium (Krone, 2001).

Zinc Deficiency

A 2020 review summarizes the myriad of conditions that can be associated with zinc deficiency (Hassan, 2020):

A zinc deficiency is characterized by impaired immune function, loss of appetite, and growth retardation. More severe cases of zinc deficiency cause diarrhea, delayed sexual maturation, hair loss, eye and skin lesions, impotence, and hypogonadism in males. Weight loss, taste abnormalities, delayed healing of wounds, and lethargy can also occur.

Zinc is also implicated in some cases of angular cheilitis (cracks in the corners of the mouth; Gaveau, 1987).

Many reputable sources report that zinc deficiency impairs immune function. One source says:

Zinc deficiency has been known for 50 years and is associated with skin abnormalities, hypogonadism, cognitive impairment, growth retardation, and imbalanced immune reactions which favor allergies and autoimmune diseases….

…[A] balanced zinc homeostasis is crucial for either defending against invading pathogens or protecting the human body against an overreactive immune system causing autoimmune diseases, chronic inflammation or allergies (Wessels, 2017).

There isn’t much research studying zinc deficiency and colds; the research mostly focuses on treating colds with therapeutic amounts. But one study on older adults suggests that correcting zinc deficiency can prevent colds and other infections. Prasad et al. (2007, University of Michigan) conducted a randomized, controlled study on zinc supplementation in men and women aged 55 to 87 years. Measurements at baseline suggested that the older participants had, on average, sub-optimal zinc status. The study lasted one year with the treatment group receiving 40 mg of zinc per day. There were 24 people in the treatment group and 25 in the placebo group. At the end of 12 months, fewer participants in the treatment group had experienced infections (29% vs. 88%, P< 0.001), including upper respiratory tract infections (12% vs. 24%, P= 0.136), and common colds (16% vs. 40%, P=0.067).

A study of healthy adults found that eating oysters, which are high in zinc, improved sleep patterns, but it’s not clear if the zinc component of the oysters was responsible (Saito, 2017, Cherasse, 2017).

Zinc Absorption and Status of Vegans

Phytates, which are commonly found in plant foods, reduce zinc absorption, and some researchers have suggested that this increases the zinc needs of vegetarians by up to 50% (Institute of Medicine, 2001).

Below is a chart showing the zinc intakes of vegans from 4 studies (larger version).

Of the 5 measurements reported, vegans met the RDA except for in the EPIC-Oxford study which found that vegan men had slightly lower zinc intakes than the RDA. The method of determining zinc intake in EPIC-Oxford, by way of food frequency questionnaire, is generally less reliable than are 3-day diet records which were used in the smaller studies in Switzerland and Germany.

These studies showed that on average vegans have lower blood zinc levels than meat-eaters but within the reference ranges. However, in the Switzerland study, 47% of vegans were below the reference range, indicating that vegans should be aware of their zinc intakes and monitor for deficiency symptoms.

Zinc and Alzheimer’s Disease

It’s not clear that any metals are the cause of Alzheimer’s Disease (AD). A 2011 meta-analysis performed by researchers from Loma Linda University and George Mason University disputes the idea that metals cause Alzheimer’s (Schrag 2011). They conclude that the findings of higher mineral levels in the brain, especially iron, have suffered from citation bias, whereas many of the findings in the literature have shown no increased levels of such metals. They conclude:

Using meta-analysis and systemic review methodologies we have identified the wide-spread misconception in AD literature that iron, and to a lesser degree zinc and copper, levels are increased in AD brain….In light of our findings it will be important to re-evaluate the brain metal-overload hypothesis in AD and critically review related research and review articles.

Even if levels of zinc are increased in the brain of people with AD, it does not mean that higher zinc intakes are the cause.

A 1998 cross-sectional study found that zinc levels in cerebrospinal fluid (CSF) were significantly lower in AD patients than in controls (.12 vs. .22 mg/l) and that serum zinc levels were the same (Molina 1998). The authors stated, “There was no significant correlation in AD patients between the CSF or serum levels of iron, copper, zinc, and manganese and the following values: age, age at onset of AD, duration of AD, and scores of the Minimental State Examination.”

A 2010 cross-sectional study found blood zinc levels to be significantly lower in AD patients compared to controls (Baum 2010).

A 2006 prospective study found that after 6 years of follow-up, dietary intakes of copper, zinc, and iron were not associated with cognitive decline. However, among the people who consumed a diet high in saturated and trans fats, a faster decline was seen with higher copper (but not zinc or iron) consumption (Morris 2006).

Finally, a 2012 study gave patients, with mild to moderate AD, 150 mg of slow-releasing zinc per day for 6 months (Brewer 2012). The zinc supplementation stabilized the AD symptoms, while the placebo group got worse. It wasn’t clear if this study was double-blinded and it could simply be that subjects with mild to moderate AD symptoms had low zinc intakes due to a poor diet, which is not uncommon. However, the researchers believed that it was due to zinc reducing copper levels. Although only one patient had to have their zinc dose lowered because copper decreased to deficiency levels, the researchers stated that anyone taking zinc supplements to stabilize AD symptoms should only do so under a doctor’s supervision due to potential copper deficiency.

The Linus Pauling Institute says that while copper deficiency is uncommon, one of the signs is an anemia that is unresponsive to iron therapy but corrected by copper supplementation (link).

In conclusion, it seems very unlikely that a modest zinc supplement could contribute to AD.

Bibliography

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Brewer GJ. Copper excess, zinc deficiency, and cognition loss in Alzheimer’s disease. Biofactors. 2012 Mar-Apr;38(2):107-13.

Cherasse Y, Urade Y. Dietary Zinc Acts as a Sleep Modulator. Int J Mol Sci. 2017 Nov 5;18(11):2334.

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. Not cited.

Gaveau D, Piette F, Cortot A, Dumur V, Bergoend H. Manifestations cutanées du déficit en zinc dans la cirrhose éthylique [Cutaneous manifestations of zinc deficiency in ethylic cirrhosis]. Ann Dermatol Venereol. 1987;114(1):39-53. French. Abstract.

Hassan A, Sada KK, Ketheeswaran S, Dubey AK, Bhat MS. Role of Zinc in Mucosal Health and Disease: A Review of Physiological, Biochemical, and Molecular Processes. Cureus. 2020 May 19;12(5):e8197.

Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. (2001)

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