What zinc is: Zinc is an essential mineral needed for the enzymes that regulate cell division, growth, healing of wounds and immune system performance. The mineral also supports normal growth and development during pregnancy, childhood and adolescence and is aids our ability to taste and smell. Meats, seafood (especially oysters) and liver are the richest sources. Strict vegetarian diets may not contain much zinc. The recommended dietary allowance, or RDA, for zinc is 8 to 11 milligrams a day for people 14 or older and 3 to 8 milligrams for children, depending on their age.
Claims, purported benefits: Cures or shortens colds, relieves prostate symptoms, prevents prostate cancer, prevents or alleviates age-related macular degeneration.
What the studies show
Colds. In lab studies, high amounts of zinc can block rhinoviruses (the leading cause of colds) from adhering to the nasal lining and/or replicating themselves. But outside the lab, controlled studies have yielded contradictory findings.
Eye health. Zinc may help protect against age-related macular degeneration or at least slow its progression in those who already have the disease.
Prostate health. Research findings have been contradictory. Notably, a 2003 study from the National Cancer Institute found that men who took more than 100 milligrams of zinc a day were twice as likely to develop advanced prostate cancer, especially if they had taken it for 10 years or more, compared with those who took no zinc. Zinc does increase blood levels of testosterone, which may promote prostate cancer.
Side effects: Long-term use of high doses of zinc can negatively affect the body's ability to absorb copper, reduce the functioning of the immune system and more. Short-term studies have found that zinc may cause nausea, a foul taste in the mouth, diarrhea, vomiting, cramps and sores in the mouth.
Bottom line: If you are a vegan, are over 60 or are for any reason not consuming adequate zinc, consider taking a multivitamin/mineral supplement containing zinc.