Zinc is an essential mineral and is found naturally in foods such as red meat, poultry, seafood, dairy products, whole grains, nuts, and legumes. Interestingly, zinc binds to proteins and is absorbed as these proteins are digested. The human body is remarkably efficient at absorbing zinc. Nonetheless, vegetarians can be at risk for zinc depletion because a chemical called phytate in grains and legumes can lower zinc absorption. Zinc is available in several different forms, including zinc sulfate, zinc gluconate, and zinc combined with manganese and other nutrients. People take zinc in tablets and lozenges by mouth, and occasionally in drops, ointments or creams, and spray form.
USES
Zinc is thought to help the immune system function optimally and is needed for appropriate cell function. Zinc is widely used for many different diseases, including pneumonia, gastric ulcers, sickle-cell disease, wound healing, Alzheimer’s disease, attention deficit hyperactivity disorder, and acne, and topically for dandruff, dermatitis, psoriasis, herpes simplex eye infections, and acne. Some other popular uses include treating the common cold, macular degeneration (an eye condition associated with aging), and serious acute diarrhea in malnourished children in third world countries. It is added to some toothpaste and mouthwash products. It is also a component of intravenous feeding nutrition for burn patients.
There is some evidence that zinc supplements may benefit people with type 1 or 2 diabetes, because zinc may help the body promote insulin production and improve its action. However, more long-term study of zinc in people with diabetes is needed. Interestingly, zinc has been added as an ingredient to some older insulin formulations to help extend their action. Overall, patients should rely on a balanced diet for appropriate zinc intake, and zinc supplements should only be taken under the supervision of a doctor.
DOSE
Recommended daily zinc intake varies depending on age and health. The upper tolerable recommended daily dose in people 19 and older is 40 milligrams (mg). For young babies, the upper level is 4 to 5 mg daily. Strict vegetarians may need as much as 50% more zinc than people on average diets. The daily dose used in one diabetes study was 30 mg.
STUDIES
• One study evaluated zinc’s role in diabetes prevention. Fifty-six obese women at risk for diabetes were given 30 mg of zinc or a placebo (dummy pill) each day for 4 weeks. The researchers monitored changes in fasting glucose, insulin concentrations, and insulin resistance. They reported there was no difference between the two groups. However, this study was only for a short period of time and only in a small number of people.
• A separate study evaluated the impact of zinc levels on heart disease in 1,050 people with type 2 diabetes. Zinc levels were measured, and the incidence of coronary heart disease death rates and heart attacks were then examined for the next 7 years. A total of 156 people died from coronary heart disease, and 254 people had a fatal or nonfatal heart attack. People with lower zinc levels had a higher risk of coronary heart disease death and other adverse cardiovascular events. The researchers speculated that zinc has antioxidant effects that protect the heart.
SIDE EFFECTS AND DRUG INTERACTIONS
Zinc supplements may cause upset stomach, such as nausea or vomiting, and a metallic taste in the mouth. Toxic side effects may occur if you take more than 40 mg daily. At higher doses, zinc can affect copper and iron levels and result in anemia. Also, too much zinc can cause diarrhea and actually weaken— instead of boost—the immune system. It can also lower good” cholesterol (HDL). There is some concern that zinc may worsen prostate disease.
Zinc may compete with the absorption of certain beneficial minerals, such as chromium, in the body. Also, calcium and iron supplements may decrease zinc absorption. Zinc may cause the body to absorb higher levels of manganese from certain supplements. High doses of zinc may interfere with magnesium in the body, yet high magnesium intake may decrease zinc absorption from plant sources.
Zinc may also interfere with absorption of some antibiotics, such as Cipro, or certain tetracyclines, such as Vibramycin. Some medications may decrease zinc levels, such as the ACE inhibitor lisinopril (Zestril), often taken by people with high blood pressure or kidney problems. Other medications that may decrease zinc levels include the cholesterol-lowering medication cholestyramine (Questran), steroids, such as prednisone, certain estrogens, certain acid-lowering drugs, such as Prilosec, or some anticonvulsants, such as phenytoin (Dilantin) or divalproex sodium (Depakote). You should also note that taking zinc supplements with black coffee instead of water might decrease zinc absorption by half.