How much zinc is too much?
Zinc is one of the most commonly utilized minerals in our bodies, and despite its crucial role in hundreds of functions, our body doesn't actually produce it or store it! That means we must take it in from supplemental sources, either through our diet or a daily supplement. The body contains 2-3 grams of zinc and about 90% is found in muscle and bone. So how much zinc should we be aiming for daily, and how much is too much?
Adequate & recommended intake
Health Canada recommends an adequate daily intake (ADI) level of 11mg for male adults and 8mg for female adults, and a maximum daily limit of 40-50 mg per day for both groups. It is important to keep in mind that many of these values are designed to meet the nutritional needs of the average healthy individual. They may not be adequate for individuals who are at risk of deficiencies, or greater need due to their unique health considerations (like diet, illness or lifestyle factors).
Am I at risk for zinc deficiency?
There are specific individuals who are at a greater risk of zinc deficiency. This includes individuals with digestive illnesses that interfere with nutrient absorption such as Crohn's disease, those who suffer from alcoholism, those following a vegan/vegetarian diet, women who are pregnant or nursing and the elderly, as zinc absorption often declines with age. Speak to your healthcare practitioner if you suspect you might benefit from higher levels of daily zinc.
How much zinc is too much zinc?
Signs and symptoms of zinc overdose
While overdosing on zinc is not common, and no reports of toxicity have been documented through the intake of dietary zinc, it is possible to overdose on supplemental zinc. Individuals who consume high supplemental amounts of zinc, typically over 100mg/day, may experience nausea and vomiting, diarrhea, abdominal or epigastric pain and flu-like symptoms (headache, chills, cough, fatigue and fever) after acute digestion. Although quite rare, there have been documented cases of intestinal bleeding and gut erosion with zinc intake above 200mg.
Acute effects: Nausea and vomiting
These are two of the most common symptoms reported with high zinc intake, since zinc is absorbed by the gastrointestinal system. Most reported cases of nausea and vomiting are documented at doses of 100-150 mg and upwards.
Very high doses of zinc, above 225 mg daily, are considered emetics, which means they trigger vomiting, usually quickly. For some individuals, doses at or above 50 mg may trigger nausea most notably. If you think you have taken an excessive amount of zinc or have become ill following zinc ingestion, please seek medical help immediately.
Does zinc interfere with other mineral levels?
Zinc is absorbed in the small intestine, along with other minerals such as copper, calcium and iron. As a result, zinc at high doses can compete with minerals for absorption and "win", resulting in less absorption and risk of deficiency.
Zinc's effect on copper levels
Studies show that supplementing long-term at much higher levels than the adequate daily intake, in the range of 100 mg of zinc per day or more, can interfere with copper absorption and may cause copper deficiency. Some cases of copper deficiency have been noted at doses of 60 mg of zinc per day. Copper deficiency can result in low iron levels, low neutrophils (an important white blood cell type that patrols the blood looking for foreign invaders) and changes in cholesterol metabolism.
Copper is a trace mineral that the body uses to help transport iron, produce energy and white blood cells, and is required at even smaller doses than zinc. The Recommended Dietary Allowance (RDA) for copper is 900 mcg daily for both men and women, with an upper supplement limit of 8000 mcg daily. For dietary sources of copper, foods like oysters, shiitake mushrooms, dark chocolate and tofu are all great options.
Balancing zinc and copper intake
To err on the safe side, Health Canada recommends that adults (aged 19 and up) who are supplementing with more than 30mg of zinc daily, take additional copper, starting at 2000 mcg and up to 8000 mcg daily. Always consult with your healthcare provider, such as a Naturopathic Doctor, before introducing any new supplements.
In general, it is good practice to take a zinc supplement away from other minerals, due to the potential interference with absorption. For instance, some individuals experience nausea when they take zinc on an empty stomach. If this occurs, try taking your zinc supplement following a meal.
Chronic effects of high zinc intake
Taking very high doses of zinc for longer periods of time may also result in more chronic, not immediately noticeable effects, like lower HDL cholesterol (the "good" kind), changes in taste, mineral deficiencies and more frequent infections.
Too much zinc can affect your immune system
This might seem strange, as we know zinc plays a really important role in how our immune system functions, and we need adequate zinc to have fully functioning immune cells. However, very high doses of zinc may actually hinder our immune system. This effect is usually related to the impact on immune cells like neutrophils from a copper deficiency, but some studies have shown that excess zinc may have a direct immune-suppressing effect as well.
A study looking at healthy participants taking more than 300 mg of zinc over 4 weeks showed that they had lower lymphocyte response, another type of white blood cell. Fortunately, most symptoms are reversed once supplementation at a high dose is stopped.
Treating a zinc overdose
If you have ingested an excessive amount of zinc, pleases seek medical help immediately. Depending on the level of ingestion, it may be life-threatening.
Poison control may advise you to consume milk, as the calcium and other mineral content can block zinc from being absorbed in your bloodstream.
Choosing a safe zinc supplement
Zinc supplements are generally very well tolerated when taken as directed. Getting in your daily zinc, and avoiding a zinc deficiency if you are at risk, can be safely achieved with a well-tolerated supplemental form like zinc bis-glycinate, which is especially gentle on the digestive tract and is well absorbed. Remember that a little goes a long way when it comes to zinc, and the beneficial impact is felt all through the body.
Disclaimer: Always consult with a qualified healthcare practitioner prior to starting any natural health supplements to understand if it's right for you. Your healthcare practitioner will be able to help make recommendations based on your health history.