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
• Absorption Differences between Zinc Supplement Formulations
• Zinc and Colds
• 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).

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 (see Zinc and Colds below). 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

Summary: Research on vegan adults suggests that many vegans might be zinc-deficient, which could impact their immune system. Zinc deficiency among vegans can be caused by a combination of low intakes and a higher amount of phytic acid in plants, which can prevent zinc absorption. It’s prudent for vegans to supplement with 5 to 10 mg of zinc per day. Anecdotally, some vegans notice a lower incidence or severity of colds after starting a zinc supplement.

Phytic acid, also known as phytate, is found in many plant foods and reduces zinc absorption; some researchers have suggested that this increases the zinc needs of vegetarians by up to 50% (Institute of Medicine, 2001).

Kristensen et al. (Denmark, 2006) analyzed zinc absorption in the same people who took turns eating a lacto-ovo-vegetarian diet and two different meat-based diets. The meat-based diets had a phytic acid to zinc ratio of 9:1, while the vegetarian diet had a ratio of 10:1. The meat-based diets also had more zinc (9.4 and 9.9 mg vs. 7.5 mg). The difference in the percentage of zinc absorbed between the diets wasn’t significant (27% for both meat diets; 24% for the vegetarian diet), but there was a significant difference in the total amount of zinc absorbed (2.6 and 2.7 mg for the meat diets; 1.8 mg for the vegetarian diet).

Klein et al. (Germany, 2023) measured the serum levels of zinc in 40 omnivores, 47 flexitarians, 45 vegetarians, and 40 vegans. Although the average serum zinc concentration wasn’t significantly lower in vegans than in meat-eaters, 42.5% of vegans fell below the reference range for serum zinc. The researchers suggest that free zinc represents the bioavailable fraction of serum zinc and could be a more reliable marker of zinc status; the concentration of free zinc was significantly lower among vegans.

We list the zinc intakes and status of vegans in the spreadsheet, Zinc Status among Diet Groups.

Vallboehmer et al. (Germany, 2025) studied the zinc status of young adults, including 65 omnivores, 45 vegetarians, and 18 vegans. Based on serum zinc concentrations below 70 μg/dL, 11%, 51%, and 67% of omnivores, vegetarians, and vegans were deficient.

The researchers tested the immune response to two types of RNA viruses to determine the participants’ capacity to mount a defense against the viruses via interferon production. Interferon responses were lower for vegetarians and vegans and were also lower for participants who were considered potentially zinc-deficient based on intakes (but who had normal serum zinc levels). The researchers administered 10 mg of supplemental zinc per day to participants who were zinc-deficient, as determined by serum zinc levels, for two weeks, resulting in increased interferon levels.

To date, this is the most in-depth research on zinc deficiency among vegetarians and vegans, but we should be cautious when a study merely finds biochemical differences between diet groups. This study implies that many vegetarians and vegans don’t have as strong an immune system as meat-eaters, but interferon is only one part of the immune system and research examining infectious disease rates would be the optimal way to determine whether zinc deficiency could be impacting the immune systems of vegans.

Absorption Differences between Zinc Supplement Formulations

Summary: Zinc supplements are available in many forms, including zinc gluconate, zinc picolinate, zinc oxide, zinc glycinate, and zinc sulphate. There isn’t enough evidence to recommend any specific form of zinc. Individuals with low stomach acid should avoid relying on zinc oxide. Because stomach acid can decrease with age, it’s best for older adults to avoid choosing zinc oxide.

Devarshi et al. (2024) conducted a thorough review of the scientific literature concerning the absorption rates of different forms of zinc. They conclude that zinc glycinate and gluconate are better absorbed than other forms.

Most of the absorption studies on zinc test only one dose. This doesn’t provide a full picture of the adaptation that might occur over time. More importantly, almost all of the research has been conducted on people without zinc deficiency. When someone doesn’t need as much zinc, forms that aren’t as readily absorbed might be an advantage. An analogy is iron, in which the absorption of non-heme iron is more responsive to the body’s iron stores than is heme-iron.

Barrie et al. (1987) write, “[T]he combined effects of zinc loading on gastrointestinal absorption, renal excretion and tissue deposition result in strong regulation of serum zinc concentrations….Short-term serum levels can be a useful method for measuring the relative uptake of zinc after a single loading. Serum zinc concentration appears to be a transient factor in the normal physiology of zinc absorption and storage.”

To be clear, I haven’t seen evidence that different forms of zinc lend themselves to the body’s downregulation of absorption; however, I don’t think we should assume that in all cases, the higher the absorption, the better. This is especially true in studies of people who aren’t zinc-deficient.

There have been four longer-term studies on zinc absorption, which are described in the spreadsheet Absorption Rates of Different Zinc Formulations: Longer-Term Studies (DiSilvestro, 2015; Siepmann, 2005; Wolfe, 1994; and Barrie, 1987). A summary is that glycinate, picolinate, sulfate, and gluconate seem to be absorbed more readily than oxide or citrate. But all four studies were done on people with apparently healthy zinc status, so it’s hard to draw conclusions.

Regarding one-dose studies:

• One study that varied stomach acid found that under high pH (low stomach acid), zinc oxide wasn’t absorbed as well as zinc oxide under low pH or zinc acetate under either condition (Henderson, 1995).
• Three studies found a similar absorption rate between zinc oxide and sulfate when added to food (López de Romaña, 2003; Rosado, 2012; Hotz, 2005).
• One study in young adults found higher absorption from gluconate and citrate than oxide (Wegmüller, 2014).

Zinc and Colds

Among individuals who are unlikely to have a zinc deficiency, some research suggests that zinc may prevent the acquisition of a cold or respiratory infection, or reduce the symptoms of a cold or respiratory infection once it has been acquired.

A Cochrane systematic review (Nault, 2024) of randomized, controlled trials found that taking zinc to prevent colds didn’t work better than taking a placebo. They found that taking zinc after developing a cold might reduce the duration of a cold for two days, but considered the evidence weak.

Another systematic review (Hunter, 2021) of randomized, controlled trials using zinc for prevention resulted in a lower risk of contracting an illness consistent with a community-­acquired viral respiratory tract infection. Zinc didn’t prevent an illness when participants were exposed to a virus as part of an experiment. When used for treatment, zinc was found to shorten the duration of symptoms and reduce their severity on day 3, but not overall.

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.

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