James G. Penland
Zinc deficiency was first described in Egyptian and Iranian adolescents more than 30 years ago and continues to be a common health problem for children living in both developing and developed countries. As many as 70 percent of school-aged children in Thailand and 34 percent of Chinese preschool children may be zinc deficient. Zinc deficiency in the United States is much less common, with studies showing that about 6 percent of girls and 10 percent of boys are zinc deficient. Such deficiency is known to impair immune function and to retard growth in children. But its impact on brain function and mental performance has been demonstrated only recently.
Zinc is known to be essential for brain development and function in animals. When mice, rats and primates are deprived of zinc during critical periods of brain development, they exhibit many behavioral deficits, particularly in memory, activity, aggression and socialization. Recent work has shown that even mild zinc deprivation of pre-adolescent monkeys results in deficits in both memory and attention. Severe zinc deprivation of adult animals has also impaired their behavior.
When adult men were treated with an agent that removes zinc from the body, they experienced more mood swings and deficits in visual perception and verbal memory. In a highly controlled, 6-month study at the Grand Forks Human Nutrition Research Center we found that men with low zinc intakes had faster, but less accurate performance on tasks measuring verbal and nonverbal memory. In another controlled study at our Center, we found that restricted zinc intakes caused men to perform more poorly on 9 of 15 cognitive and psychomotor tasks. On the other hand, taking a 30-milligram (mg) supplement of zinc each day improved visual memory in a study done with women.
The early studies of severely and moderately zinc-deficient adolescents in Egypt and Iran found "mental disturbances" and "mental lethargy" among those children. Subsequent studies of mental performance of children at risk of zinc deficiency have yielded inconsistent results. In Canada and Guatemala, young school children given an extra 10 mg of zinc daily had no significant improvement in mental performance. But a study of more than 1,000 school-aged children in China conducted by the our Center had different results. Those supplemented with 20 mg of zinc daily showed more improvement in hand-eye coordination, attention and reasoning than the children given a supplement containing most of the essential vitamins and minerals except zinc and four other minerals known to interfere with its absorption. This was the first intervention study to demonstrate in children a relationship between zinc intake and cognition and psychomotor function.
More recently, we found similar effects with zinc supplementation of school-aged Mexican-American children living in southwest Texas. These findings suggest that zinc supplementation most likely improves attention, reasoning and psychomotor function, such as hand-eye coordination. It appears that we are now beginning to uncover the role of zinc for brain function and mental performance of children, and the results of this detective work clearly will have very important implications for the world's population with suboptimal zinc intakes and others who are at risk for zinc deficiency. This work also is another example of the important work on mineral nutrition and human health and performance being conducted at YOUR Grand Forks Human Nutrition Research Center. Good sources of zinc are: oysters, beef, pork, liver, dried beans and peas, whole grains, fortified cereals, nuts, milk, cocoa and poultry.