Though zinc is best known for its potential as a cold-busting immune booster, this critical mineral is the ultimate multitasker. Found in every tissue in the human body, zinc is required for cell growth and division, thyroid hormone metabolism, reproduction, blood cell function, taste, vision and smell, blood sugar balance and physical performance. Zinc deficiency is fairly widespread, even in developed nations and estimates are that 20 – 30% of the world’s population is affected. The actual figure is likely much higher, as these numbers are based only on zinc intake by food source and don’t take into account absorption issues caused by stress, medication and other components of the modern diet. When it comes to nutrients, it’s not so much what you take in but, rather, what you absorb and what your body can use.
Vegetarians and alcoholics are at greatest risk but women taking birth control medication or hormone replacement therapy may suffer as well. Even if you don’t fall into one of those categories, you may have a zinc deficiency if you consume a high-carbohydrate diet. Whole grains contain a compound called phytic acid, which binds to and blocks the absorption of minerals including zinc. Certain forms of dairy may also inhibit absorption and high sugar intake can drastically increase urinary zinc excretion.
Symptoms of zinc deficiency include: low energy levels, ringing in the ears, poor immune function, low libido, infertility, memory issues and slow wound healing. Low zinc levels can also alter your sense of taste, leading to cravings for salty and sweet foods.
Researchers have developed a taste test to determine zinc status. The test involves oral administration of 10 mL of a zinc sulphate solution and a subsequent gauge of taste perception. Taste responses to the solution are classified as follows:
- Category 1: No specific taste or other sensation is noted, even after the solution has been kept in the mouth for about ten seconds.
- Category 2: No immediate taste noted; after several seconds a slight taste is noted, described as dry-mineral, furry or sweet.
- Category 3: A definite but not strongly unpleasant taste is experienced almost immediately and usually intensifies with time.
- Category 4: A strong and unpleasant taste is noted immediately.
The less a person tastes the solution, the poorer their zinc status. If the taste response falls in categories 1 or 2, a zinc deficiency is indicated.
The test is simple, inexpensive and can be performed at home.
Oysters contain the highest zinc content of any food, though they are not widely consumed. Grass-fed beef and lamb and pasture-raised turkey are also good sources but consuming these foods in combination with grains and legumes can dramatically reduce the amount of the mineral that is accessible to the body due to the phytic acid factor. Soaked and sprouted nuts, grains and legumes have lower levels of phytic acid, allowing for increased absorption of zinc and other minerals. Since casein has also been shown to hinder zinc absorption, it may be necessary to limit or avoid dairy consumption while eating zinc-rich foods.
Adults who consume very few animal products and eat mostly processed foods are at the greatest risk for zinc deficiency. In these cases, supplementation can be helpful. Your body absorbs zinc in supplement form much better than that from food sources. Many forms of zinc are available as over-the-counter nutritional supplements, however zinc citrate and zinc monomethionine have been shown to possess superior bioavailability, meaning your body can access and metabolize more of the mineral. Research suggests a dose of 15 to 25 mg is adequate for correcting a deficiency ( 40 mg/day is the Tolerable Upper Intake Level [UL] set by the Institute of Medicine at the National Academy of Sciences).
There are several important considerations when supplementing with zinc:
- Absorption is reduced as your body gets used to the supplement. Solution: cycle off of the supplement after 3 months of continuous use.
- Other minerals – calcium, iron – may compete with zinc for absorption. Solution: take your zinc supplement on its own, separate from other mineral supplements or multivitamins.
- Long-term use of zinc can deplete copper levels. Solution: consume more copper-rich foods, such as sesame and sunflower seeds (preferably sprouted), cashews, oysters, crab and shitake mushrooms. Some zinc supplements contain copper.