Zinc is an essential trace mineral required for a myriad of processes in human physiology. It's the second most abundant in the body after iron, but isn't stored like iron, so it must be consumed regularly through diet. Zinc originates in the soil, where it's taken up by plants. The plants are eaten by animals, then those animals are consumed by others. This leaves Zinc much more concentrated and usable from animal dietary sources. While a large percentage of the world population is deficient and prone to problems. Taking too much leads to challenges too.
Forms of Zinc
Elemental Zinc is unstable when it's by its self, and doesn't stay that way for long. When we see Zinc on a label, we assume that it is combined with other elements or compounds to form a stable salt. These salts differ in their ability to be absorbed by the human body. Some examples of these salts are: Zinc Picolinate, Zinc Acetate, Zinc Gluconate, Zinc Citrate, and Zinc methionine. Zinc attached to amino acids like methionine tends to be absorbed very well.
Zinc is Absorbed in the Small Intestines
Dietary Zinc is absorbed especially in the proximal region of the small intestine. Cells lining the intestine (enterocytes) absorb the Zinc using a carrier mediated process. This uses energy, and works best when the Zinc is coupled with an amino acid. Receptors on the cells can grab hold of the amino acid portion and yank the Zinc into them.
Animal and Plant Sources Impact Zinc Absorption
The presence of animal protein enhances Zinc absorption, while plant compounds like phytic acid make it poorly soluble and hard for the body to use. This is why folks on vegetarian diets -especially those high in grains and legumes -may experience Zinc deficiency. In fact, about one quarter of the world population may be deficient in Zinc!
Imbalances of other dietary trace minerals like Copper and Iron may reduce copper absorption. Calcium also reduces absorption, especially when mixed with plant products like phytates.
Zinc Does it All
Zinc is required for so many things in human physiology it can be hard to keep track. It's a cofactor in enzymes that speed up and direct chemical reactions in the body. For instance, it is required to make testosterone, and directs the vital enzyme carbonic anhydrase to covert carbon dioxide from cellular respiration to bicarbonate. Bicarbonate then floats around in the blood, acting like a buffer to help regulate pH. In the lungs, with the help of zinc, it is then turned back into carbon dioxide and exhaled. The shape of a protein determines how it will function. Zinc linked to amino acids causes them to fold in intricate shapes. It's thought that at least 10% of all body proteins contain Zinc linkages. This explains why animal protein is so high in it. Zinc helps with vision, and is also used to read DNA for creating proteins.
Zinc Deficiency is Widespread in Humans
While all the tissues contain considerable zinc, some organs like the kidney and liver store it. Though unlike iron, this isn't a big reservoir and won't last for long in times of deficiency. Zinc is mainly lost through the GI tract, kidneys, and the skin. The skin sheds cells and sweat, rich in Zinc. Zinc is literally everywhere in the human body, yet it isn't stored the way iron is. There's only a few days reserve of a usable form in small reservoir pools. Normal serum levels of Zinc range from 0.66 to 1.10 mcg/ml. Optimal serum ratio of Copper and Zinc is 0.70 -1.00. Zinc blood levels may be misleading though, since the body must maintain a certain level of the trace metal to maintain life. Lack of Zinc is associated with major depression, loss of appetite, impaired immune function, and even diarrhea. Zinc appears to protect the GI tract vs bacteria and viruses that cause gastroenteritis.
The General Recommendations
The US Recommended Dietary Allowance for Zinc is fairly meager -ranging up to 13 mg/day for adults. Taking over 25mg of iron may decrease Zinc absorption. High levels of Zinc may decrease copper absorption. The accepted dosing ratio for Zinc and copper is 8-15 mg of Zinc for every mg of copper.
Too Much Zinc is Toxic Too
Taking large amounts of Zinc hinders iron and copper absorption. Folks may experience loss of smell, nausea, vomiting, loss of appetite, diarrhea, and headaches. Large doses of Zinc mess with metabolism and shut down the immune system. Another issue with too much Zinc is being prone to candida and other chronic infections.
A Mechanism for Why Too Much Zinc Impacts Immunity
White blood cells require copper to create an enzyme called super oxide dismutase (SOD). SOD generates a powerful nasty radical compound called Super Oxide, which is used to kill bacteria and viruses. With too much Zinc, copper levels fall, along with the ability to make SOD.
Drugs and Zinc
Drugs may interfere with Zinc or cause negative interactions. Many antibiotics will counteract each other, resulting in both not being absorbed. Thiazide diuretics and furosemide may increase urinary excretion of Zinc. Angiotensin converting enzyme inhibitors (ACE) and angiotensin receptor blockers (ARB)s may also cause depletion.