The popularity of zinc supplements may encourage some consumers to exceed the upper limit. Excessive zinc intake interferes with copper absorption and can increase magnesium excretion. By taking zinc lozenges for colds, you can get almost four times the upper limit. Studies of the effectiveness of zinc lozenges on cold symptoms are inconclusive, with only half showing any positive effect.
A Turkish study looked at 56 heart failure patients and 30 healthy volunteers, and it found that the serum zinc levels were 11 percent lower in the afflicted group.
Various studies show zinc-deficient people experience more frequent infections due to impaired immune function, similar to that seen in age-related immune decline. Tufts University researchers showed that nursing home residents, ages 65 and older, with low-serum zinc levels were twice as likely to develop pneumonia.
A University of Washington study found that adequate dietary zinc intake was significantly associated with a 54 percent reduced risk of malignant melanoma, a rare but deadly type of skin cancer.
British scientists have found that dyslexic children often have lower levels of zinc in their sweat (which is thought to be a more useful measure than that in blood serum). In addition, animal studies have shown that zinc deficiency during pregnancy can result in learning impairment for the offspring.