Zinc deficiencies are quite common in people living in poor countries. Phytate, a substance found in unleavened bread (pita, matzos, and some biscuits) 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.^{1, 2}

People with liver cirrhosis appear to be commonly deficient in zinc.³ This deficiency may be due to cirrhosis-related zinc malabsorption.⁴

People with Down’s syndrome are also commonly deficient in zinc.⁵ Giving zinc supplements to children with Down’s syndrome has been reported to improve impaired immunity⁶ and thyroid function,⁷ 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.^{8, 9}

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 anaemia, malabsorption problems, and chronic kidney disease.¹⁰