Zinc

Figure 1. The crystal structure of Zinc.

Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is the 24th most abundant element in Earth's crust and the 2nd most abundant trace metal in humans after iron. In the human body, Zinc is stored and transferred in metallothioneins (i.e. in the membrane of Golgi apparatus inside eukaryotic cells). Zinc is the only trace metal that appears in all enzyme classes and is required for the function of over 300 enzymes and 1000 transcription factors (proteins that control the rate of transcription of genetic information from DNA to messenger RNA).  

Zinc is a major player in the growth of cells, building proteins, healing damaged tissue, and supporting a healthy immune system. Because Zinc helps cells to grow and multiply, it is critically required during times of rapid growth, such as childhood, adolescence, and pregnancy (especially for prenatal and postnatal development). Zinc is also involved with the senses of taste and smell.

Food Sources

Meats, poultry, and seafood are rich in zinc. Some good food sources include:

• Shellfish such as oysters, crab, mussels, lobster and clams
• Meat such as beef, pork, and lamb
• Poultry such as turkey and chicken
• Fish such as flounder, sardines, salmon and sole
• Legumes such as chickpeas, lentils, black beans, and kidney beans
• Nuts and seeds such as pumpkin seeds, cashews, and hemp seeds
• Dairy products such as milk, yogurt and cheese
• Eggs
• Whole grains such as oats, quinoa, and brown rice
• Certain vegetables such as mushrooms, kale, peas, asparagus and beet greens

The recommended daily intake for Zinc is 11 mg for adult men and 8 mg for adult women. For pregnant and breastfeeding women, they should consume 11mg and 12mg per day, respectively.

Taken as a Dietary Supplement

As a dietary supplement, Zinc is mainly promoted to help with Zinc deficiency. Mild forms of zinc deficiency are more common, especially in children in developing countries where diets are often lacking in important nutrients. Severe Zinc deficiency is rare, but may be higher in risk in people with the following diets or conditions:

• People with gastrointestinal diseases like Crohn’s disease
• Vegetarians and vegans
• Pregnant and breastfeeding women
• Older infants who are exclusively breastfed
• People with sickle cell anaemia
• People who are malnourished, including those with anorexia or bulimia
• People with chronic kidney disease
• People who abuse alcohol 

Symptoms of Zinc deficiency may include diarrhoea, decreased immunity, thinning hair, decreased appetite, mood disturbances, dry skin, fertility issues and impaired wound healing. 

Consuming excessive Zinc supplements may lead to Zinc toxicity. Zinc toxicity may lead to acute and chronic symptoms, including nausea and vomiting, loss of appetite, diarrhoea, abdominal cramps, headaches, reduced immune function, and decreased “good” HDL cholesterol levels. Additionally, excessive Zinc may cause deficiency in other nutrients such as interfering with the body's absorption of copper and iron. It is generally good practice to stay away from high-dose Zinc supplements unless prescribed by a doctor to treat Zinc deficiency conditions.