Think Zinc – Are You Getting Enough?

My teacher, Dr Carl Pfeiffer, was the first to put zinc on the map for mental health thanks to a girl called Lisa. Lisa was crazy but her parents had learnt how to keep her sane. Oysters. If Lisa had a couple of oysters a day her mind calmed down. Dr Carl Pfeiffer worked out it was zinc. Zinc, as you probably know, is essential for cellular growth and repair and thus found in all seeds, nuts, beans, lentils, as well as eggs, meat and fish, but nothing beats oysters.

The basic calculation for our zinc needs to support growth are 7.5mg a day. An oyster gives 5.5mg. But is that really the minimum? What’s the optimum? Few consider, or have explored what intake is needed for optimal mental or immune health.

Zinc and Immunity

Zinc is vital for immunity. Zinc is one of the most important minerals for your immune system, and one of the most commonly deficient ones. An illustration of this is its role in the thymus, a small gland that sits next to the thyroid gland behind the boney dip at the base of your throat. It’s where your T-cells go for training.

Your immune power depends to a large extent on T-cells. An example of this is HIV/AIDS where the virus destroys a certain kind of T-cells called CD4. But where do T-cells come from? And how can you make sure you’ve got enough fully functioning T-cells, because that’s like having a big and strong army. T-cells originate from bone marrow and then go to the thymus for ‘training’. They not only multiply in the thymus but turn into specific kinds of troops called helper, regulatory, cytotoxic or memory T cells.[1] But what has zinc got to do with this? In children who are low in zinc their thymus size actually shrinks and when they’re given zinc you can measure an increase in thymus size and an improvement in T-cell numbers and function. This is partly to do with a hormone called thymulin which is essential for cells to differentiate into their different roles. Thymulin production is zinc dependent.[2]

But just about everything you want your immune system to do involves zinc. Without enough you don’t grow T-cells or B-cells which make antibodies to tag invaders. Macrophages, which gobble up viruses, don’t work and your whole immune army becomes inefficient and, ultimately, grinds to a halt.[3] It’s also an antioxidant critical for the enzyme SOD, which is zinc, copper and manganese dependent so, without sufficient zinc (or manganese or copper) you can’t dampen down oxidative stress, which is a hallmark of a viral attack.

The question is how much you need and can more help your immune system to function? The optimal intake of zinc is generally considered to be the region of 15 to 20mg.

High Potency Zinc for Fighting Viral Infections

But where the story around zinc and immunity got even more interesting was a series of studies giving much higher amounts of zinc, between 50mg and 200mg a day, during an infection. The first was by George Eby, father of a 3-year-old girl with leukaemia who had a cold. She was given a tablet of zinc (200mg) and instead of swallowing it she chewed it and it dissolved in her mouth. Her cold symptoms, including sore throat, went away. Her father then ran the first ever double-blind, placebo-controlled study on zinc lozenges in 1984. I remember this because this was the year we opened the Institute for Optimum Nutrition (ION) in London and around the time that the world of nutrition was waking up to the importance of zinc.

As more studies, with varying doses and forms of zinc, got published the evidence got stronger, but not all studies worked. All the studies were for the common cold so we don’t know what the effect is for specific flu viruses. It seemed to be the amount of zinc that made the difference but there was also a debate about the form. Eby had used zinc acetate, while others used zinc gluconate. Also, did the zinc have to be released in the mouth, as in a lozenge, or could you just swallow a tablet? This debate continues.

Professor Harri Hemilä from the University of Helsinki pooled the data from seven trials giving 75mg or more of zinc as a lozenge and found that “The mean common cold duration was 33% shorter for the zinc groups of the seven included trials.”[4] That’s no small effect. Remember, high dose vitamin C reduced the duration of colds by 20% to 50% so, if these two nutrients could combined could halve the duration of a cold, and maybe flu, that’s a very big difference. No combined study has yet been done.

Professor Hemilä found no evidence that doses over 100mg are more effective and concluded that “the maximal effects of zinc lozenges may be reached by doses of some 80mg/day, if the lozenge composition is optimal, i.e. the lozenge does not contain substances that bind zinc.” If, for example, you buy a vitamin C powder using zinc ascorbate you can get significant amounts of zinc as well as vitamin C. Something to consider with lozenges is the amount of sugar used in them to hide the taste of zinc. I take a vitamin C supplement that contains 3mg of zinc. If I take high dose, eg 20 grams I get 60mg of zinc, plus the 10mg in my multivitamin, which gets me into this high zinc zone.

While zinc is clearly anti-viral getting it into infected cells is a challenge. That’s where quercetin and hydroxychloroquine[5], the controversial anti-malarial drug used for covid-19, come in. They are what’s called a ‘zinc ionophore’. Like a Trojan horse they sneak zinc into infected cells where it leashes its anti-viral action, including against SARS-CoV-2[6]. As a nutritionist I’d prefer to use quercetin, rich in red onions, as my Trojan horse. Supplementing 500mg of quercetin should help zinc to work during viral infections.

How Much Zinc is Optimal?

Researchers in North Dakota gave 200 school children in the 7th grade zinc supplements and found that those taking 20mg of zinc a day, as opposed to those taking 10mg (the US RDA) or placebo, had faster and more accurate memories and better attention spans within three months.[7] Zinc is not only essential for healthy methylation, along with B vitamins, but it is also necessary co-factor for our ability to make use of essential fats, with omega-3 being the main structural fat in the brain. An example of this is study on healthy men found that 25mg of zinc a day normalised fat metabolism while 10mg did not.[8]

In truth, there is not enough evidence to establish an optimal intake of zinc but it is likely to between 15 and 25mg a day. In other words, twice the recommended Reference Nutrient Intake of 10mg for men and 8mg for women. Probably a third of people do not achieve even this and very few, except vociferous nut eaters, will achieve 15mg a day. With a good, wholefood diet along the lines I recommend you may achieve 10mg. That’s why I recommend supplementing an additional 10mg a day to achieve roughly 20mg.

In summary, my take home view is that it is always good to increase your zinc intake during an infection and also consider trying zinc lozenges to see if they work for you.

  • To keep your immune defences up make sure you get enough zinc on a daily basis, both by eating zinc rich foods – nuts, seeds, beans, lentils, meat, eggs, seafood.
  • Also take a daily multivitamin providing 10mg of zinc. This is the best way to ensure your total intake is at least 15mg a day.
  • Consider taking more during an infection, up to a maximum of 75mg, but this is for short-term use only. On a daily basis don’t take more than 50mg and, for extra safety, I’d say that more than 25mg is unlikely to give any health advantage. It is better to take most of your zinc in a multivitamin with some copper and manganese.
  • ImmuneC, the vitamin C supplement I take provides 3mg of zinc per tablet and just under 1g of vitamin C. So, if I take one an hour during infection for 20 hours (assuming 4 hours off during sleep – I usually take two tablets in the middle of the night if I wake up) that’ll give me 60mg of zinc, plus the 10mg in my multi. This is not, however, the same a chewing a lozenge which may have other ‘local’ advantages for throat infections.
  • Lozenges should provide a daily total of at least 75mg of zinc, eg a 15mg lozenge taken six times a day.
  • You neither need, nor should take these high levels of zinc for more than the short-term duration of a cold, eg up to one week.

More Information

In the Patrick Holford range of supplements at HOLFORDirect, Optimum Nutrition Formula, ImmuneC and ImmuneC High Strength powder contain zinc.


[1] T Aydemir et al, Zinc transporter ZIP8 (SLC39A8) and zinc influence IFN‐γ expression in activated human T cells. Journal of Leukocyte Biology, (2009), 86(2):337-48. []

[2]  J Bach and M Dardenne, Thymulin, a zinc-dependent hormone. Medical Oncology and Tumor Pharmacotherapy, (1989), 6(1):25-9.

[3]  A Prasad, Zinc in Human Health: Effect of Zinc on Immune Cells. Molecular Medicine, (2008), 14(5-6): 353–357.

[4]  H Hemilä, Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage Journal of the Royal Society of Medicine Open, (2017), 8(5).

[5]  Rahman MT, Idid SZ. Can Zn Be a Critical Element in COVID-19 Treatment? Biol Trace Elem Res. 2021 Feb;199(2):550-558. doi: 10.1007/s12011-020-02194-9.

[6] Panchariya L, Khan WA, Kuila S, Sonkar K, Sahoo S, Ghoshal A, Kumar A, Verma DK, Hasan A, Khan MA, Jain N, Mohapatra AK, Das S, Thakur JK, Maiti S, Nanda RK, Halder R, Sunil S, Arockiasamy A. Zinc2+ ion inhibits SARS-CoV-2 main protease and viral replication in vitro. Chem Commun (Camb). 2021 Sep 30;57(78):10083-10086. doi: 10.1039/d1cc03563k.

[7] Penland J.G., April 4, 2005, Experimental Biology 2005(conf report); also see related work by the author –

[8] Jung H Suh, Sarah J Zyba, Mark Shigenaga, Christine M McDonald, Janet C King, Marginal Zinc Deficiency Alters Essential Fatty Acid Metabolism in Healthy Men, The Journal of Nutrition, 2021;, nxab425,