What Are the Consequences of Excess Zinc?

Zinc is an essential nutrient that is frequently overlooked. The best dietary source is oysters, which are too expensive–or possibly too weird–for a lot of people to consume very often. Diets rich in plants often contain phytates that can interfere with the absorption of zinc. Consequently, it’s no wonder that if your healthcare providers think about zinc at all, they are likely to assume you are getting enough or possibly be concerned that you might be low. Are there problems associated with taking excess zinc through supplements? Some readers report concerns.

Does Excess Zinc Raise Alkaline Phosphatase?

Q. A few weeks ago, you answered a question about zinc supplements. You warned that taking zinc long-term might result in nerve pain and raise alkaline phosphatase levels. I had high levels for years, and my doctors thought I might have problems with my liver or bones, though they could not find anything. I even had a bone scan.

I had been eating Raisin Bran each morning and frequently consumed nuts. In addition, I took PreserVision AREDS 2 daily as well as a multivitamin that contains zinc. I would also take zinc lozenges to ward off colds. When I read about the connection between zinc and alkaline phosphatase, I changed my breakfast cereal, stopped the multivitamin and zinc for colds and gave up eating nuts. I am still taking PreserVision AREDS 2, as I have early macular degeneration and my ophthalmologist recommends it.

Three months later, a blood test showed my alkaline phosphatase was normal. They are still normal after three years now. I had undergone a number of tests and quite a bit of worry because of the zinc.

A. Your story is a great reminder that minerals like zinc don’t just appear in dedicated pills or lozenges, but also in food. Since your alkaline phosphatase is now normal, you seem to have found a path that is working.

Zinc RDA

The recommended intake (RDA) of zinc is 11 mg for men and 8 to 12 mg for women. (The higher amount is for women who are breastfeeding.) The tolerable upper intake level has been set at 40 mg/day. As we mentioned, oysters are an exceptionally rich source, with around 30 mg per serving. That is roughly ten times more than other good sources such as beef, fortified breakfast cereal or pumpkin seeds.

We have long worried about the high dose of zinc (80 mg) in the AREDS formula. It does contain 2 mg copper to help offset the danger of an imbalance. Part of the AREDS 2 study tested 25 mg of zinc with the rest of the supplement ingredients and found it equally effective (JAMA, May 15, 2013).  But because the number of participants in that arm of the study was low, they did not provide a clinical recommendation. If scientists conduct a well-controlled follow-up study, perhaps they will set zinc at the lower dose.

Supplements Supplying Excess Zinc:

Q. My retina specialist wants me to take PreserVision for macular degeneration. A daily dose has 80 mg of zinc. I also take a multivitamin containing 20 mg of zinc.

Credible sources state that 40 mg/day is the safe upper limit for zinc intake. Should I be concerned about excess zinc?

A. You are correct that the tolerable upper limit established by the Food and Nutrition Board is 40 mg for adults. Daily doses above 50 mg can interfere with copper absorption. This can impair immune response and lower HDL cholesterol.

High levels of zinc can also interfere with iron absorption and metabolism (Clinical and Experimental Medicine, Feb. 2024). You are smart to be paying attention to this possible problem.

We suggest that you check with your eye doctor about whether you might switch to a lower dose. The standard AREDS (Age-Related Eye Disease Studies) and AREDS2 formulas contain 80 mg of zinc per day. However, some products provide the rest of the formula without zinc. If that is not an option, you might consider a multivitamin that does not contain minerals. There are several formulations available.

Is 100 mg per Day Too Much Zinc?

Q. Some years ago, I read about the benefits of zinc in reducing the frequency of respiratory tract infections. I have been taking 100 mg of the mineral daily ever since, along with 1,000 mg vitamin C.

I used to get frequent, severe and long-lasting colds. Since I began taking the zinc and C combo, I’ve had fewer and milder colds.

I read recently about people experiencing zinc toxicity from denture creams. Am I asking for trouble?

A. It is possible to develop copper deficiency as a reaction to taking in zinc at a level of 100 to 300 mg per day over a long period of time (American Journal of Clinical Nutrition, Feb., 1990). You may be flirting with copper deficiency. Have your blood tested and consider cutting back to under 50 mg of zinc daily. The recommended dietary allowance of zinc for an adult man like you is 11 mg per day.

This post has focused on the potential dangers of excess zinc. One of the most popular reasons to take zinc supplements is to fend off colds and other respiratory infections. Here is an up-to-date, in-depth summary of the evidence on that from our friends at Examine.com.