Zinc Deficiency

Zinc is needed for the catalytic activity of hundreds of enzymes, and it plays a role in immune function, protein and DNA synthesis, wound healing, cell signaling and division, growth and the sense of taste (NIH Office of Dietary Supplements). The body holds only about 1.5 g (women) to 2.5 g (men), mostly in muscle and bone, so it depends on a steady daily intake. Zinc deficiency means that supply is too low for those jobs. It ranges from rare severe deficiency, with a clear rash, diarrhea and hair loss, to marginal deficiency, which is hard to diagnose and often causes vague or no obvious symptoms. The effects depend on age. In infants and young children, diarrhea is a common sign. In older children, hair loss (alopecia), delayed growth and frequent infections become more common, and deficiency during growth periods results in growth failure. In adults and older people, chronically low zinc is described with poor appetite, mental lethargy, skin changes, delayed wound healing and altered taste and smell; in men, low testicular function (hypogonadism) is reported. Severe deficiency, with skin lesions, diarrhea, hair loss, mental disturbances and repeated infections, can be fatal if untreated, but it responds to zinc replacement. In pregnancy, deficiency in populations with low intakes raises the risk of maternal illness and poor birth outcomes, although a 2021 Cochrane review of 25 trials found not enough evidence that routine zinc supplements improve pregnancy outcomes. Deficiency is common worldwide but uncommon in well-fed populations. An estimate based on national food supplies suggests 17.3% of the world's population is at risk of inadequate zinc intake, mainly in Sub-Saharan Africa and South Asia, where diets rely on cereals and legumes whose phytate binds zinc. In the United States most people get enough, but about 15% of adults have intakes below the average requirement. Higher-risk groups include people with inflammatory bowel disease, celiac disease, chronic liver disease or alcohol use disorder, people who have had bariatric surgery, vegetarians and vegans, pregnant and breastfeeding women, and exclusively breastfed infants after 6 months. Supplements help most when deficiency or a high risk of it is real. In a Cochrane review of 80 trials of preventive zinc in children aged 6 months to 12 years (205,401 children), zinc cut diarrhea incidence by about 13% but had a very small effect on height, no clear effect on lower respiratory infections or malaria, more vomiting and a negative effect on copper status; its authors judged the benefits to outweigh the harms where deficiency risk is high; a separate Cochrane review of zinc for treating childhood diarrhea does not support its use in well-nourished children. Taking zinc without need has costs: 50 mg or more a day for weeks can impair copper absorption (case reports describe copper deficiency with anemia and nerve damage), and high intakes cause nausea, vomiting and stomach upset.

• •Diarrhea (a common sign in infants and children)
• •Slow growth or stunting in children
• •Hair loss (alopecia)
• •Frequent or repeated infections
• •Skin rash or dermatitis (severe)
• •Acral rash with diarrhea and hair loss (inherited form)
• •Poor appetite
• •Altered taste and smell
• •Slow wound healing
• •Mental lethargy, mood or cognitive changes
• •Low testicular function in men (hypogonadism)

• •Low intake of absorbable zinc (little meat, fish or seafood)
• •High-phytate diets based on unrefined cereals and legumes
• •Vegetarian and vegan diets
• •Pregnancy and breastfeeding (higher needs)
• •Exclusive breastfeeding after 6 months of age
• •Inflammatory bowel disease (Crohn's disease, ulcerative colitis)
• •Celiac disease
• •Bariatric surgery that removes part of the gut
• •Chronic liver disease and cirrhosis
• •Alcohol use disorder
• •Chronic kidney disease
• •Sickle cell disease (possibly iron chelation therapy)
• •Thiazide diuretics (more zinc lost in urine)
• •Acrodermatitis enteropathica (inherited zinc-transporter defect)

Low intake of absorbable zinc is the most common root cause worldwide. Zinc from meat, fish and other seafood is well absorbed, whereas zinc from beans, nuts and whole grains is bound by phytate, which can cut absorption anywhere from over 50% to as little as 5% depending on the diet. Populations eating mostly unrefined cereals and few animal foods have the highest rates of deficiency, and in a meta-analysis of 26 studies vegetarians had lower zinc intakes (about 0.9 mg a day) and lower serum zinc than non-vegetarians. Needs rise in pregnancy (3 mg a day more), lactation (4 mg a day more), infancy and adolescence. Human milk zinc falls by about 75% between the first and ninth month, so breast milk alone cannot meet an infant's needs after 6 months. Other causes are poor absorption or extra losses: inflammatory bowel disease (about 15-40% affected), celiac disease (about half of newly diagnosed patients at high risk of inadequacy), bariatric surgery that removes part of the gut, chronic liver disease (in a Japanese series, 28.1% of 1,973 patients, and 49.8% of those with cirrhosis, had serum zinc below 60 mcg/dL), chronic kidney disease, sickle cell disease, alcohol use disorder (30-50%), and thiazide diuretics, which increase zinc loss in urine. A rare inherited form, acrodermatitis enteropathica, is caused by mutations in SLC39A4, the gene for a zinc transporter, and shows as the triad of acral rash, diarrhea and hair loss. Zinc status can also look low without true depletion: infection, inflammation, recent meals and the time of day all change blood zinc.