Zinc is a nutritionally essential mineral needed for catalytic, structural, and regulatory functions in the body.
The RDA (recommended daily allowance) for adult women and men is 8 mg a day and 11 mg a day of zinc, respectively.
Severe zinc deficiency is a rare, genetic or acquired condition. Dietary zinc deficiency, often called marginal zinc deficiency, is quite common in the developing world, affecting an estimated 2 billion people. Zinc deficiency can cause impaired growth and development in children, pregnancy complications, immune dysfunction, and increased susceptibility to infections. Long-term consumption of zinc in excess of the tolerable upper intake level of 40 mg a day for adults can result in copper deficiency.
Zinc bioavailability is relatively high in meat, eggs, and seafood. Zinc is less bioavailable from whole grains and legumes due to the inhibitory effects of phytic acid on absorption of the mineral.
Vitamin C, or L-ascorbic acid, or ascorbate, is an essential nutrient for humans, a water-soluble vitamin. Humans, unlike most animals, are unable to synthesize vitamin C, so it is an essential dietary component.
Vitamin C is required for the biosynthesis of collagen (an essential component of connective tissue), L-carnitine, and certain neurotransmitters, it is also involved in protein metabolism.
Vitamin C is also an important physiological antioxidant and has been shown to regenerate other antioxidants within the body, including alpha-tocopherol (vitamin E). Vitamin C regenerates vitamin E by reducing vitamin E radicals formed when vitamin E scavenges the oxygen radicals.
Vitamin C plays an important role in immune function and improves the absorption of nonheme iron, the form of iron present in plant-based foods.
Approximately 70%–90% of vitamin C is absorbed at moderate intakes of 30–180 mg a day. At doses above 1 g a day, absorption falls to less than 50% and absorbed, unmetabolized ascorbic acid is excreted in the urine.
Insufficient vitamin C intake causes scurvy, which is characterized by fatigue or lassitude, connective tissue weakness, and capillary fragility.
Cells accumulate vitamin C. The total body content of vitamin C ranges from 300 mg (at near scurvy) to about 2 g.
High levels of vitamin C are maintained in cells and tissues, and are highest in leukocytes (white blood cells), eyes, adrenal glands, pituitary gland, and brain.
Relatively low levels of vitamin C are found in extracellular fluids, such as plasma, red blood cells, and saliva.