Can You Boost Your Immune System with Extra Zinc?

Most people would like to improve their immune function at this time of year. Viruses that cause colds and influenza are everywhere and even vigorous hand washing may not protect you from coming down with an upper respiratory tract infection. Could supplements help, including extra zinc? Are there potential hazards?

Will Astragalus Help Boost Your Immune System?

Q. Some years ago I asked a doctor what to do to bolster my immune system. He recommended a combination of astragalus, NAC and vitamins A and D.

I have not taken it routinely. However, when I feel a cold sore coming on, I take these. If I don’t have all three on hand, I take two astragalus immediately and two more at night. The cold sore is usually gone! If it is still threatening the next day, I repeat the astragalus. Gone–and what heartache and pain avoided. Magic for me!

I take nothing routinely. Should be worried about astragalus in any way?

A. Most people report that astragalus and NAC (N-acetylcysteine) may be helpful against respiratory infections like colds. When it comes to cold sores, however, people generally report good results from L-lysine oral supplements.

You challenged us with the idea of using astragalus against cold sores. We did find research suggesting that this ancient Chinese herb can activate immune system cells (Evidence-based Complementary and Alternative Medicine, June 26, 2014).  These cells fight the herpes virus responsible for cold sores.

Sporadic use of astragalus supplements appears to be relatively safe. People with autoimmune diseases should probably avoid this herb, however. There is also the possibility that astragalus could reduce the effectiveness of some prescription medications (International Journal of Molecular Sciences, May 28, 2025).  Please check with your pharmacist to make sure it won’t cause unexpected problems with your usual prescriptions.

Are There Dangers from Long-Term Zinc?

Q. I have been taking zinc at night for several years because I read it could help boost the immune system. In my opinion, it helps against the common cold. My husband has gotten one twice, but I didn’t catch it from him either time. Was the zinc responsible? I would like to know more about the dangers of taking zinc long term.

A. Taking zinc for colds has been controversial for some decades. A recent meta-analysis concluded that zinc supplementation doesn’t reduce the risk of catching a cold, but it can help shorten the duration of symptoms (Cochrane Database of Systematic Reviews, May 9, 2024). Zinc gluconate lozenges appear to be most helpful.

Taking zinc supplements long term might upset the balance between zinc and copper. In some cases, this could result in nerve pain (StatPearls, Dec. 11, 2022). Keep reading for more information about the pros and cons o zinc for immune function.

Extra Zinc and Immunity:

Zinc is one of those minerals that gets very little respect. People often take calcium and magnesium, but rarely even think about zinc. Yet this mineral is crucial for the immune system. It activates T cells, which are crucial for combatting bacterial and viral infections. Your natural killer cells cannot function fully without adequate levels of zinc.

A research team from Tufts University recruited 25 older people who were low in zinc to participate in a double-blind, placebo-controlled study. The research was published in The American Journal of Clinical Nutrition (March 2016). It demonstrated that supplementing older residents in a nursing home with 30 mg of extra zinc daily for three months raised zinc levels in the bloodstream.

In addition, the investigators found that the group that got 30 mg of zinc compared to placebo (5 mg. of zinc) had better immune function. The number of T cells in their bodies went up, a measure of immune system enhancement. The T cells seemed more responsive in that they were able to proliferate more effectively in response to stimuli that simulated infection.

The Consequences of Low Zinc Levels:

The authors of this study had previously discovered that older people living in nursing homes frequently have low levels of zinc in their bodies. When this crucial mineral is deficient, there is a greater likelihood of developing pneumonia. The death rate is also higher when people are low in zinc.

Who’s at Risk of Low Zinc?

Nursing home residents are not the only people with low zinc levels. Older people in general may be more vulnerable to this mineral deficiency. One suggestion is that senior citizens have trouble absorbing zinc as well as younger people. Vegetarians may also be a greater risk of zinc deficiency. People taking blood pressure drugs that contain diuretics (hydrochlorothiazide for example) or ACE inhibitors (such as captopril, enalapril or lisinopril) could also be low in zinc.

Don’t Overdose:

The recommendation that our colleague Tieraona Low Dog, M.D., suggests is 15 to 25 mg of extra zinc daily for those on diuretics or ACE inhibitors. The Tufts researchers gave their older nursing home residents 30 mg daily. We would discourage anything over that since too much zinc can be toxic. The upper limit is 40 mg daily.

Watching Out for Too Much Zinc:

Q. You had a question about zinc in PreserVision eye supplements for macular degeneration. My eye doctor suggested I take it, but I found that it upset my stomach.

I was told that this formula has a high dose of zinc and that may have caused my digestive discomfort.

My eye doctor said the important ingredients are lutein and zeaxanthin. He suggested I just take those two. I have been and have had no stomach problems since.

A. Your solution sounds sensible. As long as your eye doctor is tracking your progress, this adaptation makes sense. Read on for more information on excess zinc.

Extra Zinc Could Interfere with Copper Balance:

Q. When the COVID-19 pandemic started, my husband began taking a bunch of supplements to enhance his immune system. He read that zinc was especially helpful against viral infections. As a result, he has been taking 50 mg daily for the past five years. Is this safe?

A. The recommended dietary allowance (RDA) for zinc is 11 mg per day, so your husband has been taking considerably more than he may need. Zinc has direct antiviral activity as well as playing an important role for the immune system and even the cardiovascular system (International Journal of Molecular Sciences, April 12, 2023).

Daily doses of 50 mg of zinc taken for many weeks or months could lead to copper deficiency. This may reduce immune function, undermining your husband’s goal. It may also lower helpful HDL cholesterol. The Food and Nutrition Board of the National Academies of Sciences has established 40 mg of zinc as the tolerable upper intake level for adults.

The RDA for copper is 900 micrograms (mcg) for adults. Our bodies use it in processes of energy production, neurotransmitter synthesis and iron metabolism, among others. Shellfish, liver, nuts and seeds, whole grains and chocolate supply this essential mineral.

Learn More:

If you find this whole topic of interest, you will want to listen to our interview with Dr. Low Dog on our syndicated radio show. Other podcasts that might be worthwhile include Show 1170: What Makes Your Immune System an Elegant Defense? Show 1217: Natural Ways to Keep Your Immune System Strong, and Show 1457: How to Strengthen Your Immune System for Cold and Flu Season.  You can also learn more about preventing and treating respiratory infections in our eGuide to Colds, Coughs & the Flu.