We assessed blood kinetics, biochemical responses, and clinical effects in 5 adult men and 5 adult women who voluntarily ingested ~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.

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.

After ~90 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 μg/L (range: 12–33 μg/L) and 25 μg/L (range: 15–46 μg/L), respectively. In women, mean cobalt whole blood and serum concentrations were 53 μg/L (range: 6–117 μg/L) and 71 μg/L (range: 9–149 μg/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.

Peak cobalt whole blood concentrations ranging between 9.4 and 117 μg/L were not associated with clinically significant changes in basic hematologic and clinical variables. This study was registered at clinicaltrials.gov as NCT01990794.