Effects and blood concentrations of cobalt after ingestion of 1 mg/d by human volunteers for 90 d1-3

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 similar to 1.0 mg Co/d (0.080-0.19 mg Co . kg(-1) . d(-1)) 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 similar to 90 d of dosing, mean cobalt blood concentrations were lower hi men than in women. Mean cobalt whole blood and serum concentrations in men were 20 mu g/L (range: 12-33 mu g/L) and 25 mu g/L (range: 15-46 mu g/L), respectively. In women, mean cobalt whole blood and serum concentrations were 53 mu g/L (range: 6-117 mu g/L) and 71 mu g/L (range: 9-149 mu g/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 +/- 1.3 mL/min) than in men (5.5 +/- 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 mu g/L were not associated with clinically significant changes in basic hematologic and clinical variables. This study was registered at clinicaltrials.gov as NCT01990794.