Microminerals (trace elements) Zinc Dr. Sherin Bakhashab

Zinc Sources: Zinc is found in a variety of food. Oysters contain more zinc than other food, but red meat and poultry provide the majority of zinc. Other food sources include: beans, nuts, whole grain and dairy products. Recommended daily allowance (RDA): 10-20 mg/ day. Plasma Zinc: 70-150 µg/dl

Absorption Zinc absorption occurs mainly in small intestine, especially from the duodenum. Only 20% of dietary zinc is absorbed by the body. A zinc-binding factor, secreted by the pancreas, helps the absorption of zinc. Zinc is delivered to metal-binding protein (metallothionin) in the intestinal mucosal cells. Absorption of zinc suppress copper and iron absorption. Phytates decrease zinc absorption, where phytic acid forms a highly insoluble complex with zinc, which inhibit zinc absorption. Zinc absorption affects the copper absorption directly. Zinc absorption affects the iron absorption indirectly. ↑ Zn absorption lead to ↓ Cu absorption as both competing for binding to intestinal receptor (metallothionin) → ↓ cereulloplasmin which decrease Fe absorption and transport.

Functions Zinc is required for mobilization of vitamin A from the liver and subsequently maintain the normal concentration of vitamin A in plasma. It plays a role in the tissue repair and wound healing. Zinc is important for growth and reproduction. Zinc forms a complex with insulin in B islet cells or the pancreas. This helps crystallization, storage and release of insulin. Zinc is essential component of a number of enzymes example: Alkaline phosphatase Carbonic anhydrase Superoxide dismutase (also contains Cu) Carboxypeptidase

Functions Zinc is an important structure in zinc-finger motif (finger like structure) that stabilizes the structure of a number of proteins. Zinc-finger regulates the gene expression by acting as transcription factor (binding to DNA and influencing the transcription of specific genes).

Excretion The excretion of Zn is mainly in the feces, this is consisted of unabsorbed dietary Zn. Very little amount of Zn is excreted in urine. MAO catalyses deamination of monoamines

Deficiency Zinc deficiency rarely results from decreased intake. It may occur in case of liver cirrhosis and in alcoholics due to increased excretion in urine. Deficiency leads to: Poor appetite Growth retardation Hypogonadism Delayed wound healing and falling of hair. MAO catalyses deamination of monoamines