Q. I take 50 milligrams of zinc daily, but it looks like you should take only 40 milligrams per day. Is it OK to continue? What are the consequences of too much zinc?
A. Junaidah B. Barnett, PhD, a scientist in Tufts' HNRCA Nutritional Immunology Laboratory who has studied zinc, replies: "The Upper Limit (UL) of the essential mineral zinc intake for adults is 40 milligrams per day. This includes intake from dietary, fortified and supplementary sources. We should get most of our nutrients from food. Good food sources of zinc include seafoods (such as oysters and crabs), beef and poultry. Good plant sources of zinc such as whole grains, beans, nuts and seeds add valuable fiber, protective antioxidants and phytonutrients, among many other benefits, to the diet. Those plant foods, however, contain phytate, which binds minerals such as zinc to form complexes that are not completely broken down during digestion, decreasing their bioavailability.
"It is important to note that phytate compounds found in rich plant sources of zinc have been shown to have antioxidant properties that offer protection against cancer, cardiovascular disease and diabetes. Limiting the intake of animal sources of zinc, on the other hand, is likely a good move towards a more healthful lifestyle. This is because animal-based foods high in saturated fat and cholesterol have been associated with increased risk of various chronic diseases.
"To ensure adequate intake of zinc (8 milligrams for women and 11 milligrams for men), be sure to consume foods rich in zinc daily. If you are already consuming a diet high in zinc and meeting your dietary requirements, it is not advisable to take additional zinc in the form of supplements. With high intake of zinc through food sources, there is no need to be concerned about overconsumption, as the body will compensate accordingly. Overconsumption of zinc usually occurs when supplements are consumed rather than using foods.
"High zinc intakes (150-450 milligrams per day) have been reported to inhibit copper absorption, sometimes resulting in copper deficiency, associated anemia, reduced immune function, and reduced levels of high-density or 'good' cholesterol. Intake of 80 milligrams per day of zinc in the form of zinc oxide for an average of 6.3 years in the Age-Related Eye Disease Study (AREDS) has been associated with a significant increase in hospitalizations for genitourinary issues. Even moderately high intakes of zinc of about 60 milligrams per day for up to 10 weeks have been reported to reduce a copper-containing enzyme (a marker of copper status). Zinc supplements also have the potential to interact with several types of medications (such as antibiotics and diuretics). As such, be sure to discuss your zinc intake with your healthcare provider."