Zinc is the second most abundant mineral in your body after iron. It is mostly stored in muscles, bones, prostate, and the liver - but is found in almost all body tissues.
Zinc aids in enzyme function to control DNA expression, vitamin A metabolism, cell membrane stability, and your senses of smell and taste, among other things. The recommended daily allowance is 11mg for men and 8mg for women - or 11mg if pregnant or lactating. The maximum tolerable intake is 40mg daily (1).
Zinc is primarily absorbed in the jejunum, the second part of your small intestine. Dietary sources of zinc include pork, lamb, beef, nuts, legumes, and yeast. Plant sources have less absorption because of a complex called phytate.
Phytate inhibits zinc absorption by up to 50%, which is further worsened when calcium is also present. When ingested with animal proteins, zinc forms complexes with digested peptides (small proteins) promoting its absorption. This effect is not seen with single amino acids however. Citrate, primarily in human and animal milk, promotes zinc absorption (2).
Supplemental zinc is variably bioavailable, with zinc citrate and picolinate being the best followed by zinc sulfate, acetate and gluconate. Zinc oxide is poorly bioavailable and should be avoided as a supplemental compound. Between zinc citrate and picolinate, both are equally bioavailable, but zinc citrate may be better retained as opposed to picolinate which has been shown to increase urinary zinc excretion.
Co-ingestion of iron rich and zinc rich foods impairs zinc absorption. Elevated serum zinc impairs copper absorption, but copper has no effect on zinc absorption. Other metals such as cadmium and tin (found in potatoes, leafy greens and tomatoes) also decrease zinc absorption. High blood protein like albumin, promotes zinc absorption because this protein is the main transport molecule for the divalent cation (3).
Zinc interferes with antibiotic absorption, specifically the fluoroquinolone group whose names end in “-floxacin” used to treat urinary and respiratory tract infections.
Zinc also decreases tetracycline antibiotic group absorption. This group is primarily used to treat pneumonias (azithromycin/ Z-pack) or tick/mosquito-borne diseases (doxycycline).
Thiazide diuretics, used to treat high blood pressure, named chlorthalidone or hydrochlorothiazide increase urinary losses of zinc. Ask your health care provider if zinc supplementation while on this class of medications is right for you.
Zinc is ubiquitously utilized by enzymes throughout the body. It has a catalytic role in aiding enzymes to appropriately fold proteins, which is essential for correct protein function.
Zinc also plays a structural role in cellular and nuclear receptors that respond to estrogen, thyroid hormones, and fat soluble vitamins like D and A. Zinc also is a cofactor for transcription factors which control which genes are expressed.
Collagen synthesis and wound repair mandate zinc as a cofactor for transcription factors and enzymes (tiny machines) called metalloproteinases to promote auto-debridement and migration of the cells called keratinocytes, which form a water-tight protective barrier in injured skin. In bacterial or other infections, zinc acts as an anti-oxidant via metallothioneins to buffer reactive oxygen species and bacterial toxins (4).
Zinc plays a role in the maturation and function of almost all immune cells like neutrophils, macrophages natural killer T cells, and other T and B cells. Macrophages are cells that consume pathogens, they can use a high concentration of zinc intracellularly to kill pathogens they phagocytose.
Some chronic disease can be delayed or prevented with appropriate zinc ingestion. Adequate zinc intake has been significantly correlated with a 10-50% decreased incidence of type II diabetes mellitus.
Zinc is essential for insulin creation, release and utilization. Insulin release from the pancreas co-occurs with zinc release. Zinc then acts to stimulate cellular glucose uptake alongside insulin.
Zinc supplementation has also been shown to improve blood pressure, blood glucose control, LDL cholesterol levels and overall metabolic syndrome/pre-diabetes prevention due to its role in insulin function (5).
Age related macular degeneration progression can be delayed by zinc intake; it does not prevent AMD but slows disease progression. Zinc can treat acute and chronic diarrhea by blocking intestinal secretions.
Zinc has been promoted to expedite recovery from the common cold – a main mechanism being competitive inhibition of ICAM-1, the molecule that rhinovirus uses to attack your nose.
Some studies have shown that taking at least 75mg/day of zinc in the form of lozenges or cough syrups can reduce cold symptoms by up to 33%.
While Zinc alone can be effective in boosting your immune system, it's most effective when coupled with diet and exercise.
Although 75mg/day is a large dose, the use of zinc at a level of up to 180mg/day for two weeks has been shown to be safe. In other words, the adverse effects of zinc toxicity can be avoided at this level, suggesting that short-term, high-intake of zinc can be highly beneficial.
If you begin to over-supplement zinc to a dangerous degree, nausea will likely be your first warning sign to decrease or stop zinc therapy.
Zinc-deficient children experience stunted growth. Both adults and children with low zinc have decreased appetites, impaired immune function and increased susceptibility to diarrhea, pneumonia and malaria, as well as difficulty with night vision.
In severe zinc deficiency, people experience hair loss, impotence, diarrhea, hypogonadism, eye/skin lesions, weight loss, delayed wound healing, taste abnormalities, and mental lethargy.
In males, zinc deficiency results in decreased testicular volume and weight, hypogonadism (explained more below), and dysregulated spermatogenesis.
Extreme zinc deficiency has been linked to disease processes such as major depressive disorder, schizophrenia and multiple sclerosis. Those at risk for deficiency include people with alcohol use disorder, pregnant and lactating women due to zinc’s crucial role in fetal and infant development, as well as those with sickle cell disease (6).
Zinc plays many roles in the human body, including promoting healthy growth of nails and hair. If you're experiencing brittle nails, or reduced nail growth, zinc supplementation can potentially improve nail growth, or nail health.
Again, Zinc alone may not be the answer to nail health. A balanced diet is the first place to focus on when trying to have more healthy nails.
In the majority of people, zinc supplementation should not cause constipation. Much like being nauseous, the majority of people that use zinc supplements will not experience stomach pain or nausea.
That being said, if you are experiencing constipation or nausea, you may want to reduce or eliminate your zinc supplementation. Talk to your doctor if you have concerns sypmtoms that you believe may be related to your zinc consumption.
Those at risk for zinc toxicity are most commonly people who overuse denture creams by ingesting more than 1.5g of zinc per day. Additionally, zinc toxicity is common from inhalation during jobs like welding, galvanizing, brass plating and electroplating, as well as the use of some makeup and sunscreen.
Zinc inhalation leads to "metal fume fever" which is characterized by flu-like symptoms including cough, shortness of breath, fatigue, muscle aches, excessive thirst and salivation, and a metallic taste (7).
Short term excessive zinc ingestion can cause you to vomit blood, injure the kidneys (the organs that filter your blood and make urine) and liver (another filter and protein-making organ) leading to blood clotting abnormalities.
Long term toxicity impacts your bone marrow (your blood-making tissue), leading to low blood counts of all cell lines and affects your spinal cord causing numbness and loss of motor function starting at your fingers and toes and moving upward. These latter two toxicities occur due to zinc-induced copper deficiency, explained above.
The male reproductive system relies heavily on zinc for antibacterial effects, testosterone synthesis and sperm maturation.
Male fertility has been directly linked to zinc stores, the average infertile male contains up to 1/3 less zinc than a typical male. This is because seminal fluid contains 10 times the concentration of zinc than in your blood.
The prostate is a gland responsible for 30% of seminal fluid volume, with high concentration of citrate, a metabolic intermediate which zinc plays a crucial role in sequestering in the gland.
When ejaculated, citrate is used to maintain the integrity of sperm heads as well as thin semen which allows for faster sperm motility to find and fertilize the egg more easily. In the testicles, zinc supports germ or immature sperm cells in their progression through spermatogenesis, think of this like sperm puberty (8).
We know that zinc is important in immune function elsewhere in the body, it is also important in fighting bacteria that are nearby or enter the male reproductive tract, being able to neutralize notoriously difficult pathogens such as spore-forming and gram negative bacteria.
FSH and LH are hormones made by the anterior pituitary gland in the brain which stimulate cells in the testicles, both hormones require zinc for synthesis. Their receptors in the testes rely on zinc to transmit their signal.
FSH stimulates Sertoli cells leading to sperm maturation. LH stimulates Leydig cells to synthesize and secrete testosterone.
5α-Reductase, the enzyme that intracellularly transforms testosterone into its most active form, dihydrotestosterone, requires zinc as a cofactor. Without adequate zinc, your body with neither produce adequate testosterone nor be able to utilize it to it’s fullest capacity (9).
Men who are zinc deficient and supplement with zinc can expect significantly increase their serum testosterone, a couple studies have shown almost a doubling in testosterone production. In these cases, it may be beneficial to supplement with 20mg daily instead of the generally recommended 11mg daily. Be careful not to exceed 40mg daily total zinc intake for longer than 2 weeks to avoid the zinc toxicities outlined above.