Circadian variation of plasma cobalamin, transcobalamin-bound cobalamin and unsaturated binding capacity of transcobalamin and haptocorrin in healthy elderly.

Blood samples were drawn every second hour during a 24-h period from healthy elderly subjects. Plasma levels of cobalamin, albumin, transcobalamin-bound cobalamin and unsaturated binding capacity of transcobalamin and haptocorrin were determined. During night, all components decreased in parallel with plasma albumin. The nocturnal decreases were therefore ascribed to plasma volume changes due to bed-rest. Reports on the recently proposed role of cobalamin for the biological clock were reviewed, but the proposed role could not be explained by this study.