Calcium bioavailability from heated oyster shell-seaweed calcium (active absorbable algae calcium) as assessed by urinary calcium excretion

The bioavailability of heated oyster shell-seaweed calcium (active absorbable algae calcium, AAA Ca) was compared to that of calcium carbonate by measuring increases of urinary calcium excretion after oral load. Eight normal male volunteers ingested 1000 mg calcium in the form of either calcium carbonate (CaCO₃) or AAA Ca in a crossover design with a 1-week interval between the two tests. The urinary calcium/creatinine (Ca/Cr) ratio was measured from 4h before to 6h after the administration at 2-h intervals. Urinary calcium excretion 4–6 h after oral ingestion of AAA Ca was 249 ± 119% (SD) of the baseline level, which was significantly higher than that after calcium carbonate, 170 ± 103% (SD) (P = 0.039). Paired comparison of the increment of urinary Ca/Cr over the pretest level was also significantly greater 4–6h after the ingestion of AAA Ca (0.21 ± 0.14) than that after calcium carbonate (0.132 ± 0.158) (P = 0.025). AAA Ca is thus suggested to be more biologically available than calcium carbonate in human subjects.