Context: Other sources include fortified food and dietary supplements, which come in various forms. A 1998 review concluded that zinc oxide, one of the most common supplements in the United States, and zinc carbonate are nearly insoluble and poorly absorbed in the body. This review cited studies which found low plasma zinc concentrations after zinc oxide and zinc carbonate were consumed compared with those seen after consumption of zinc acetate and sulfate salts. However, harmful excessive supplementation is a problem among the relatively affluent, and should probably not exceed 20 mg/day in healthy people, although the U.S. National Research Council set a Tolerable Upper Intake of 40 mg/day.

Question: What is the most common supplement in the US?
Answer: zinc oxide

Question: Why is zinc carbonate poorly absorbed in the body?
Answer: nearly insoluble

Question: What is the recommended daily dose of zinc supplement in healthy adults?
Answer: 20 mg/day

Question: What is the Tolderable Upper intake of zinc?
Answer: 40 mg/day

Question: What is the only common supplement in the US?
Answer: Unanswerable

Question: Why is zinc carbonate perfectly absorbed in the body?
Answer: Unanswerable

Question: What is the recommended daily dose of zinc supplement in unhealthy adults?
Answer: Unanswerable

Question: What is the Intolerable Upper Intake of zinc?
Answer: Unanswerable