Effect of Zinc on Glucose Homeostasis

Inclusion Criteria: * Amish men or women who are 18 to 80 years old * Prediabetes (HgbA1c = 5.7-6.4% or fasting glucose levels 100-125 mg/dL) Exclusion Criteria: * Pregnant * Currently breastfeeding * History of severe gastrointestinal disorders or upper gastrointestinal surgery * Has hemochromatosis, cancer, liver disease, kidney disease, cardiovascular disease, or other coexisting malignancy * Hemoglobin \< 12.5 g/dl (male) or \< 11 g/dl (female) * Severe hypertension (blood pressure \> 160/95 mm Hg) * Has a creatinine greater than 2.0 mg/dl, aspartate aminotransferase (AST) or alanine transaminase (ALT) greater than 2 times the upper limit of normal, hematocrit (Hct) less than 32%, or thyroid-stimulating hormone (TSH) less than 0.4 or greater than 5.5 milli-international units (mIU) per liter. * At the discretion of the study physician or PI, taking medications that affect the outcomes of the study including, but not limited to, corticosteroids, anti-psychotic agents, protease inhibitors, oral contraceptives, estrogens, niacin, and some classes of antidepressants, statins, and antihypertensive medications * Zinc hypersensitivity * Use of denture adhesive containing zinc * Taking other medications or zinc-containing supplements and is unwilling or cannot safely, in the opinion of the study physician, discontinue their use at least 2 weeks prior to protocol initiation * Any other condition that would, in the opinion of the investigator, place them at an unacceptable risk or render them unable to meet the requirements of the protocol.