- RDA – Adult males (11 mg); adults females (9mg)
- UL – 40 mg/day
- Bioavailability is higher in animals/animal products than plant-based sources due to phytates
- Iron supplements can decrease zinc absorption
- Excessive zinc supplementation can induce a copper deficiency
- Food Sources – Meat, eggs, oysters, lobster, crab, legumes, nuts, dairy
Recommended Dietary Allowance (RDA)
The RDA for adult males is 11 mg and 9mg for adult females. RDA values vary significantly with age. In the United States it is estimated that average dietary zinc intake is 13 mg/day for adult men and 9 mg/day for adult women.
Most zinc in the body can be found in the muscle and in the bone. Zinc has many important functions in the body. Zinc is key in enzymatic functions related to insulin production, taste perception, vitamin A metabolism, wound healing, spermatogenesis, growth of the developing fetus, and in digestive enzymes. Zinc has structural importance in the body as well. Zinc fingers are amino acids sequences high in cysteine and histidine which bind zinc and are necessary for protein folding and function. When zinc is not present, protein structure is altered and the function of proteins are lost. Superoxide dismutase, a protein and powerful antioxidant in the body, requires zinc.
Additionally, metallothioneins are a class of protein which bind zinc – they are important in the uptake, transport, and regulation of zinc. These metallothioneins modulate oxidative stress and regulate gene transcription.
Zinc has several regulatory functions in the body as well. Zinc is important for gene repression and activation. Zinc plays a role in apoptosis (programmed cell death) and in the proper functioning of the immune system. Zinc has a role in cytokine gene relation. Zinc is also a regulator of cell signaling pathways; these include hormone release and nerve impulse transmission. Zinc is found abundantly in the central nervous system. It influences synaptic transmission by affecting NMDA and GABA receptors.
Zinc absorption is inhibited by phytates. These phytates are found in products such as grains and legumes. The bioavailability of zinc is higher in foods such as meats, eggs, and seafoods and lower in whole grains and legumes. Zinc absorption may be inhibited by calcium. Zinc absorption is inhibited by intake of supplemental iron (38-65 mg/day) but not by the iron found in foods.
Severe zinc deficiency is rare but dietary zinc deficiency (marginal zinc deficiency) is estimate to affect 2 billion people.
In children, zinc deficiency can cause stunted growth and immature sexual development. In adults, it can cause impaired digestion and absorption, poor motor and cognitive ability, impaired vitamin A metabolism which can lead to vision problems, a weakened immune system, alopecia (hair loss), skin lesions, nail dystrophy, and delayed wound healing.
Toxicity/Excess/Upper Intake Level (UL)
The UL for zinc is 40 mg/day. Zinc toxicity is typically due to zinc supplementation and can cause nausea, vomiting, diarrhea, headache, fatigue, and induce a copper deficiency.
- Oysters, 6 medium, cooked – 27-50 mg – 493% DV
- Beef, 3 oz, cooked – 3.7-5.8 mg – about 30-40% DV
- Beans, baked, 1/2 cup – 0.9-2.9 mg – about 10-20% DV
- Cashews, 1 oz – 1.6 mg – 11% DV
- Chickpeas (garbanzo beans), 1/2 cup, 0.5-1.3 mg – 6-9% DV
- Almonds, 1 oz, 0.9 mg – 6% DV
- Peanuts, 1 oz, 0.9 mg – 6% DV