Temporal variation of serum levels of vitamin B12, folate, iron and total iron-binding capacity.

The influence of food ingestion and time of day on the serum levels of B12, folate, iron and total iron-binding values was studied. Food intake had no influence on serum B12, serum iron and total iron-binding capacity (TIBC) levels, but serum folate rose rapidly. Serum B12 showed no change with time of day. Serum iron and TIBC fell significantly from 8 a.m. to 8 p.m. Folate initially rose significantly over 5 h then fell at 12 h, but this fall did not reach statistical significance. Over a period of 1 year serum iron fell, but TIBC showed no significant change. Subjects without pernicious anaemia but with low B12 levels showed no significant change in serum B12 over 4 years.