Zinc is an essential mineral that supports immune function, promotes wound healing, and plays a role in your sense of taste. Short-term zinc use may help support immunity during a cold, but taking high doses for extended periods can increase the risk of health problems.
1. Copper Deficiency
High zinc intake can reduce the body’s absorption of other minerals, including copper. Zinc and copper are absorbed in the small intestine using the same transport system. When zinc intake stays high, less copper enters the bloodstream.
Copper supports energy production and helps maintain healthy red blood cells and nerves. Over time, low copper levels can lead to serious health problems.
Copper deficiency can cause:
- Anemia (low red blood cells)
- Weakened bones
- Nerve problems, such as numbness or trouble walking
- More frequent infections
2. Low Blood Cell Counts
Taking zinc supplements every day for several months can lower red or white blood cell counts. High zinc intake can reduce copper levels, and copper is needed to make healthy blood cells.
Low red blood cell counts (anemia) can cause:
- Fatigue
- Weakness
- Pale skin
- Shortness of breath
- Headaches
- Dizziness
Low white blood cell counts (leukopenia) can make it harder for the body to fight infections.
3. Lower HDL (Good) Cholesterol Levels
Zinc can affect how the body manages fats in the blood, including cholesterol. Research examining the effects of long-term zinc supplementation on cholesterol yields mixed results, and outcomes can depend on overall health and dosage.
Some studies suggest that zinc supplements may lower total cholesterol, low-density lipoprotein (LDL) or “bad” cholesterol, and triglycerides, especially in people with conditions such as diabetes or heart disease.
Some research suggests that long-term zinc use may lower high-density lipoprotein (HDL) cholesterol, or “good” cholesterol. HDL helps remove LDL from the bloodstream, which supports heart health. When HDL levels are too low, the risk of heart disease may increase over time.
4. Weakened Immune System
Short-term zinc supplementation can support the immune system and help the body respond to illnesses such as the common cold. However, taking high doses of zinc for a long time can have the opposite effect, weakening immunity. Excess zinc can interfere with the production and function of neutrophils, a type of white blood cell that helps fight bacterial infections.
When neutrophil function is impaired, the body becomes more vulnerable to infections. Over time, people who take zinc long-term may get sick more often or notice that minor wounds take longer to heal.
5. Nerve Damage and Neurological Issues
Taking high doses of zinc for extended periods can damage the nervous system. Excess zinc can impair the body’s ability to absorb copper, leading to low copper levels. Copper is essential for maintaining the health of the brain, spinal cord, and nerves.
Low copper levels can damage the protective coating around nerves and interfere with the transmission of nerve signals. Over time, this can lead to serious neurological problems, including:
- Spinal cord damage (myelopathy)
- Nerve damage that causes pain or tingling (neuropathy)
- Vision problems caused by optic nerve damage (optic neuropathy)
These conditions can affect movement, sensation, and vision. Neurological damage linked to long-term high zinc intake is not reversible, and symptoms may not improve even after stopping zinc supplementation. Symptoms of nerve damage from excess zinc can include:
- Numbness or tingling
- Muscle weakness
- Balance problems
- Vision problems
- Bladder or bowel problems
6. Digestive Problems
Taking zinc for longer than six weeks can lead to gastrointestinal problems, including:
- Stomach pain
- Nausea
- Vomiting
- Diarrhea
Prolonged high zinc intake may also increase the risk of pancreatitis, which is inflammation of the pancreas.
How Much Zinc Do You Need?
The amount of zinc you need each day depends on your age and sex. Most adult men need 11 milligrams per day, and most adult women need 8 milligrams. You can get zinc from foods such as oysters, meat, fish, poultry, dairy products, beans, nuts, seeds, and fortified breakfast cereals. Many people get enough zinc from food alone.
The safe upper limit for zinc is 40 milligrams per day for adults. This limit includes zinc from food and supplements combined. Taking more than this amount regularly can increase the risk of harmful effects.
Some research studies use higher doses of zinc for short periods to study its effects on cold symptoms. These short-term doses may exceed the daily upper limit, but they are not meant for daily or long-term use. The 40-milligram limit applies to ongoing daily intake.
Safe Zinc Supplementation Tips
Short-term zinc use for several days during a cold is generally safe for most people. While zinc supports healing and immune function, higher doses do not provide added benefits when used long-term. The risk of side effects increases when daily intake stays above 40 milligrams for several weeks or longer.
To reduce risk:
- Keep total zinc intake from food and supplements below 40 milligrams per day.
- Take zinc with food to reduce stomach upset.
- Focus on zinc-rich foods instead of supplements when possible.
- Choose multivitamins that include both zinc and copper to support your body’s mineral balance.
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