That question is perhaps more easily answered after considering the general role of zinc in nutrition. It was not until the early 1960s that zinc was first identified as an essential micronutrient in humans. Because the human body cannot manufacture zinc, it must be obtained from dietary sources or vitamin supplements. Current USDA recommended allowances are in the range of 8–11 milligrams per day for healthy adults, an amount that can be obtained by eating balanced meals or a bowl of certain breakfast cereals. Curiously, individuals suffering from chronic zinc deficiency exhibit a variety of symptoms ranging from skin disorders to diminished growth and development to cognitive dysfunction, depending on the severity of the condition.
That zinc contributes to overall brain health is not necessarily surprising, especially given its emerging role as a modulator of neurotransmission. There is mounting evidence that suggests zinc modifies communication between certain neurons, particularly within the hippocampus — a region of the brain strongly engaged in learning and memory formation — as well as in other parts of the brain that govern olfactory, auditory, and somatosensory perception. Mice genetically engineered in such a way that their hippocampal neurons cannot accumulate zinc tend to develop comparably to normal mice, but have impaired spatial, contextual, and social memory function — particularly when auditory or visual cues are required. Such data indicate zinc is probably beneficial for memory formation.
On the other hand, like many things in life, too much zinc can also be problematic. Mice dosed with artificially high levels of zinc in water over a three-month period actually exhibited a net reduction in the amount of zinc in the hippocampus, as well as a decrease in receptors and other proteins that facilitate neurotransmission. These mice had significantly impaired performance in tests designed to measure spatial memory and other behavioral assays relative to control groups. The findings from this study suggest that, at least in mice, excessive zinc consumption can have deleterious effects.
The Food and Nutrition Board of the National Academy of Medicine recommends a tolerable upper intake level of 40 milligrams per day for adults across all dietary and supplementary sources in the absence of other medical advice. Taken together, the best evidence supports that adequate zinc intake is important for learning and memory formation, but in moderation.
Jacob M. Goldberg is an assistant professor of chemistry. His research interests span the fields of chemical biology, bioinorganic chemistry, and metalloneurochemistry. He and a collaborator from the University of Pittsburgh recently received an award of $134,000 from the Picker Interdisciplinary Science Institute for their project “Chemical Probes for Synaptic Zinc.” They will develop and prepare a new generation of small-molecule sensors that will be used to detect and quantitate zinc ions in the brain.
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