Zinc deficiencies are quite common in people living in poor countries. Phytate, a substance found in unleavened bread (pita, matzos, and some crackers) significantly reduces absorption of zinc, increasing the chance of zinc deficiency. However, phytate-induced deficiency of zinc appears to be a significant problem only for people already consuming marginally low amounts of zinc.
Even in developed countries, low-income pregnant women and pregnant teenagers are at risk for marginal zinc deficiencies. Supplementing with 25-30 mg per day improves pregnancy outcome in these groups.312, 313
People with liver cirrhosis appear to be commonly deficient in zinc.314 This deficiency may be due to cirrhosis-related zinc malabsorption.315
People with Down's syndrome are also commonly deficient in zinc.316 Giving zinc supplements to children with Down's syndrome has been reported to improve impaired immunity317 and thyroid function,318 though optimal intake of zinc for people with Down's syndrome remains unclear.
Children with alopecia areata (patchy areas of hair loss) have been reported to be deficient in zinc.319, 320
The average diet frequently provides less than the Recommended Dietary Allowance for zinc, particularly in vegetarians. To what extent (if any) these small deficits in zinc intake create clinical problems remains unclear. Nonetheless, a low-potency supplement (15 mg per day) can fill in dietary gaps. Zinc deficiencies are more common in alcoholics and people with sickle cell anemia, malabsorption problems, and chronic kidney disease.321