1. Immune system function: Zinc is necessary for the development and function of immune cells, including white blood cells and T cells. It helps to maintain the integrity of the skin and mucous membranes, which serve as a barrier against infections.
2. Growth and development: Zinc is essential for the growth and development of children, particularly during fetal development and infancy. It is necessary for the synthesis of proteins and for cell division and differentiation.
3. Wound healing: Zinc plays a critical role in wound healing, as it is required for the synthesis of collagen, which is the main structural component of connective tissue. It also helps to promote the growth of new blood vessels, which is necessary for the healing of wounds.
4. Sense of taste and smell: Zinc is required for the development and maintenance of the sense of taste and smell.

1. Animal sources: The best sources of zinc are animal products, particularly red meat, poultry, seafood, and dairy products.
2. Plant sources: Zinc is also found in plant sources, including whole grains, legumes, nuts, and seeds.
3. Supplements: Zinc supplements are available in various forms, including zinc gluconate, zinc sulfate, and zinc acetate.

Zinc deficiency can occur due to inadequate intake of dietary zinc, malabsorption, increased losses of zinc from the body, or increased physiological requirements. Certain populations are at a higher risk of zinc deficiency, including pregnant and lactating women, infants and young children, the elderly, people with gastrointestinal disorders, and vegetarians and vegans who consume little or no animal products.

The symptoms of zinc deficiency can include:

1. Impaired immune function: Zinc is essential for the normal development and function of immune cells. Zinc deficiency can impair immune function and increase the risk of infections, especially in children.
2. Delayed growth and development: Zinc is critical for normal growth and development, especially during fetal development and childhood. Zinc deficiency can result in stunted growth, delayed sexual maturation, and impaired neurological development.
3. Skin and eye disorders: Zinc is involved in the synthesis of DNA and protein, which are essential for the growth and repair of skin and tissues. Zinc deficiency can cause dermatitis, skin lesions, and impaired vision.
4. Loss of appetite and weight loss: Zinc deficiency can cause loss of appetite, taste disturbances, and weight loss.
5. Impaired cognitive function: Zinc plays an important role in brain development and function. Zinc deficiency can impair cognitive function and memory.
6. Impaired fertility and reproduction: Zinc is essential for normal reproductive function in both men and women. Zinc deficiency can impair fertility, fetal development, and increase the risk of birth defects.
7. Diarrhea and other gastrointestinal problems: Zinc deficiency can cause diarrhea and other gastrointestinal problems, especially in children.

If left untreated, severe zinc deficiency can lead to immune dysfunction, growth retardation, and other serious health problems.