Comparative Absorption of Vitamin B12 Analogues by Normal Humans. II. Chloro-, Sulfato-, Nitro- and Thiocyanato- vs Cyanocobalamin

Abstract
The comparative absorption of several cobalamins by normal humans was determined by urinary excretion, fecal excretion and blood level measurements, and by fecal excretion determinations with rats. Radioactive (C06O labeled) cobalamins were employed for the excretion studies. All evidence supports the contention that the non-cyano cobalamins are less readily absorbed from the gastro-intestinal tract than is orally administered vitamin B12.