Zinc is a metallic element that reacts with hydrochloric acid when it's in its elemental state. This reaction generates the very flammable element H2, or hydrogen gas. Despite the fact that your stomach produces hydrochloric acid, the zinc in food and supplements doesn't react with stomach acid, because the zinc is not in elemental form.
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Zinc is in a group of elements from the periodic table called transition metals. These metals have variable reactivity and occur in nature in elemental form to varying degrees. Zinc occurs in nature both in elemental form -- as a shiny gray metal -- and in the form of a salt. Humans and many other organisms depend upon a certain amount of nonmetallic zinc -- that is, zinc in salt form -- to maintain cellular function.
Zinc and Hydrochloric Acid
While not all metals react with hydrochloric acid, or HCl, some do. A metal's ability to react with HCl depends upon the metal's so-called activity, where metals with high activity react with HCl. Metallic zinc's activity is high enough to allow it to react with HCl, which produces H2 gas and the compound zinc chloride, or ZnCl2, explains Dr. Martin Silberberg in his book “Chemistry: The Molecular Nature of Matter and Change."
Zinc as a Mineral
You take in zinc anytime you consume certain foods, especially meats and shellfish. Zinc plays an important role as an essential mineral, explains Dr. Lauralee Sherwood in her book "Human Physiology." A number of your enzymes require zinc in order to function, where an enzyme is a chemical that helps reactions take place faster than they would otherwise. Many of the metabolic enzymes that you use to help process nutrients depend upon zinc.
Zinc in the Body
While you have HCl in your stomach -- it assists in digestion of food -- you don't produce either H2 or ZnCl2 when you consume zinc in food. This is because the zinc you take in through food or supplement sources is not in metallic form. Instead, it has lost some of its electrons, forming positively charged particles called zinc ions. The body doesn't use metallic zinc, and the zinc in food doesn't react with HCl.