Zinc

 Main Characteristics

• Vital component for the synthesis and activity of more than three hundred enzymes.

• Participates in the synthesis and degradation of: carbohydrates, proteins, lipids and nucleic acids.

• Plays an important role in the regulation of gene expression.

• Its function in the body is subdivided into three categories: structural, enzymatic and regulatory

• It is present in food in organic form (proteins and phytates) or in the form of inorganic salts (supplements or fortified foods).

• Zinc in the body is controlled by gastrointestinal absorption, uptake and distribution, as well as its excretion through the skin, kidneys and feces, which is regulated by a homeostatic mechanism.

• After being absorbed, it is transported to the liver, where it is then bound to albumin or another protein, and performs its function in tissues.

• It is important to note that the presence of concomitantly consumed glucose increases the absorption of the mineral, which occurs mainly in the proximal part of the small intestine by passive diffusion or protein transport.

• In some situations, such as intense physical exercise or high ambient temperatures, zinc excretion through sweat may increase.

• In situations where daily zinc intake is increased, it is metabolized and excreted through urine, but the most common way is through feces.

 

Main Functions and Mechanisms of Action

• Structural:

Genetic regulation (reinforcing DNA transcription factors)

Antioxidant action (responsible for destroying the superoxide radical)

Action on vitamin D and retinoic acid receptors (through gene expression)

 • Enzymatic:

Action on the catalytic activity of many enzymes (through electron receptors)

Acts on the immune system and healing for the synthesis and action of T lymphocytes and fibroblasts

• Regulatory:

Essential in cognitive activity and memory (acts on apoptosis and regulates the activity of protein kinase c)

It is essential for the action of insulin, thymus, thyroid, adrenal and testicular hormones

Acts on the modulation of prolactin, DNA replication, and protein synthesis:

• Acts as an insulin regulator (being an important component of its synthesis)

• Acts in the prevention of hypothyroidism (in the conversion of thyroxine to triidothyronine)

• helps the pancreas (in its digestive function)

• acts on the reproductive system (is responsible for sperm maturation, ovulation and fertilization)

 

Bioavailability

• Zinc bioavailability is controlled by environmental and physiological factors, therefore, even with adequate daily intake, zinc deficiency may occur if zinc bioavailability in the diet is low.

• One of the causes of zinc deficiency may be low bioavailability, as there are several foods that have components that can interfere with zinc absorption.

 

Possible interactions

• Serum zinc depletion may occur when using: oral contraceptives, loop and thiazide diuretics, H2 receptor antagonists, D-penicillin, ethambutol and zidovudine (AZT).

Interaction between Nutrients

• Calcium: Doses of 600 mg of calcium reduce zinc bioavailability by 50%

• Phytates: These in turn reduce zinc absorption when they form complexes in the intestine between phytate and zinc. This occurs in the presence of whole grains, legumes and soy-based infant formulas, as well as the presence of calcium in the diet. However, when a certain protein is consumed in the diet, this can increase the availability of this mineral, even in the presence of phytates.

• Iron: The interaction between zinc and iron can occur both in excess and in deficiency, which is why it is important to maintain homeostasis, since the two minerals are chemically similar and can compete for the same absorption site.

• Copper: There appears to be an antagonism mechanism between these minerals, since high concentrations of zinc induce the synthesis of metallothionein, which when bound to copper accumulates in the enterocytes, preventing its transfer to the plasma, apparently causing a deficiency of this mineral.

• Cadmium: In the presence of this heavy metal, it binds to zinc, forming a complex in the gastrointestinal tract, and both are excreted. Therefore, polluted environments and smoking habits increase the need for zinc intake.

 • Vitamin A: There are two relevant factors to be described. The first is that zinc functions as a cofactor for the synthesis of retinol-binding protein, and the second occurs through an oxidation/reduction reaction between vitamin A and zinc that occurs in the intestine, liver, testicles, and retina. In the deficiency of both, it is difficult to initiate the nocturnal visual cycle, which is necessary for adaptation to the dark.

• Protein: Increases bioavailability by forming a complex, preventing zinc from being absorbed.

 

Scientific evidence regarding the effectiveness of supplementation

• In the immune system, zinc plays a role in suppressing the phosphorylation of the protein that sequesters NF-kappaB in the cytoplasm (inflammatory processes), as well as in hypersensitivity reactions, in the response of T lymphocytes, and in the activity of natural killer cells. Therefore, its deficiency affects the body's defense mechanisms, as it has anti-inflammatory and antioxidant properties.

• In rheumatoid arthritis, a study with patients with arthritis demonstrated a decrease in swelling, stiffness of the hands, longer duration of light physical exercise, and quality of life.

• In patients with bowel cancer, positive results were obtained with supplementation of 21 mg/day of zinc and 200 mg/day of selenium.

• In the reproductive system, it is more important to mention that zinc helps in the production of sperm and fetal and child development. Supplementation is essential, as its deficiency can affect cognitive and motor development and bone mass, delay in sexual maturation, and impotence.

• In pregnant women, zinc supplementation is important for treating acne, constipation, mood swings, and hair loss, which are usually caused by excessive folic acid supplementation (5 mg), which is most commonly used to prevent spina bifida.

• In the gastrointestinal tract, zinc is important for the production of stomach hydrochloric acid, and its deficiency can cause hypochlorhydria or achlorhydria, in addition to impairing taste and causing other intestinal disorders.

• There are studies that show that in thyroid disorders, zinc and selenium supplementation could increase the activity of T3 (deiodinases I and II) and normalize TSH concentrations.

• Zinc acts as a stimulator of bone formation and increases the activity of vitamin D, thus preventing osteoporosis, so supplementation is important in cases of deficiency and for maintaining bone mass.

• A study observed a decrease in total cholesterol, triglycerides and HDL cholesterol, considering doses of 100mg/day, and a reduction in glycosylated hemoglobin with doses of 30mg, verifying its importance in the prevention of diabetes mellitus and cardiovascular diseases.

Risks of overdose

 • One of the greatest pieces of evidence of its toxicity is that high levels of Zinc can lead to Copper deficiency, causing diarrhea, dizziness, drowsiness, vomiting, loss of muscle coordination and lethargy.

 

Food sources

Food Household measure – Grams (g) Zinc content (mg)

Raw oysters 12 units – 168 g 63.80

Beef liver 1 small steak – 80 g 4.24

Ground beef (20% fat) 3 tablespoons – 75 g 4.76

Steamed shrimp 13 units – 104 g 1.60

Cooked salmon 1 fillet – 100 g 0.70

Skinless chicken breast 1 small fillet – 70 g 0.70

Cooked black beans 1 tablespoon – 25 g 0.28

Cooked lentils 1 tablespoon – 24 g 0.30

Whole-grain yogurt 1 cup – 165 g 1.00

Cooked white rice 2 tablespoons – 60 g 0.24

Cooked potato 1 unit – 135 g 0.40

Avocado 4 tablespoons – 120 g 0.70

Cooked spinach 2 tablespoons – 50 g 0.37