Effects and blood concentrations of cobalt after ingestion of 1 mg/d by human volunteers for 90 d

Background: Over-the-counter cobalt supplements are available for sale in the United States, but little is known regarding their clinical effects and biokinetic distribution with long-term use. Objective: We assessed blood kinetics, biochemical responses, and clinical effects in 5 adult men and 5 adult women who voluntarily ingested w1.0 mg Co/d (0.080–0.19 mg Co $ kg 21 $ d 21 ) of a commercially available cobalt supplement over a 3-mo period. Design: Volunteers were instructed to take the cobalt dietary supplement in the morning according to the manufacturer’s label. Blood samples were collected and analyzed for a number of biochemical variables before, during, and after dosing. Hearing, vision, cardiac, and neurologic functions were also assessed in volunteers before, during, and after dosing. Results: After w90 d of dosing, mean cobalt blood concentrations were lower in men than in women. Mean cobalt whole blood and serum concentrations in men were 20 mg/L (range: 12–33 mg/L) and 25 mg/L (range: 15–46 mg/L), respectively. In women, mean cobalt whole blood and serum concentrations were 53 mg/L (range: 6–117 mg/L) and 71 mg/L (range: 9–149 mg/L), respectively. Estimated red blood cell (RBC) cobalt concentrations suggested that cobalt was sequestered in RBCs during their 120-d life span, which resulted in a slower whole blood clearance compared with serum. The renal clearance of cobalt increased with the serum concentration and was, on average, lower in women (3.5 6 1.3 mL/min) than in men (5.5 6 1.9 mL/min). Sex-specific differences were observed in cobalt absorption and excretion. There were no clinically significant changes in biochemical, hematologic, and clinical variables assessed in this study. Conclusion: Peak cobalt whole blood concentrations ranging between 9.4 and 117 mg/L were not associated with clinically significant changes in basic hematologic and clinical variables. This study was registered at clinicaltrials.gov as NCT01990794. Am J Clin Nutr doi: 10.3945/ajcn.113.071449.