Serum vitamin vitamin B12 levels were determined in 199 women who were on a regimen of oral contraceptives of either the combination or sequential type and in a control group of 196 women. The group using oral contraceptive agents (OCA) had significantly lower serum levels of vitamin B12 vitamin as compared to those of the control group. A total of 19 women using OCAs had serum vitamin B12 levels that were lower than normal values. However, the Schilling test and urinary methylmalonate excretion in this group were normal. The OCA group had a significantly lower total serum vitamin B12 binding capacity, a lower total transcobalamin I level, and a higher transcobalamin III level. Our study suggests that the fall of serum vitamin B12 in OCA users is due to the changes in vitamin B12 binders of serum and does not represent vitamin B12 deficiency. Therefore, according to our data, there is no justification for vitamin B12 supplementation in users of oral contraceptives.
PIP: Serum vitamin B12 levels were determined in 199 women who were on a regimen of either the sequential or combination oral contraceptive (OC) for 4 months and a control group of 196 women. All subjects were interviewed regarding their diet, previous pregnancies, significant sickness, and medications. The B12 value was originally determined by L. leichmannii microbiological assay in 169 women using OCs and 166 control subjects. The group using OCs had significantly lower serum levels of vitamin B12 vitamin as compared to those of the control group. 19 women using OCs had serum vitamin B12 levels that were lower than normal values. The Schilling test and urinary methylmalonate excretion in this group were normal. The OC group had a significantly lower total serum vitamin B12 binding capacity, a lower total transcobalamin 1 level, and a higher transcobalamin 3 level. The fall of serum vitamin B12 in OC users appears to be due to changes in vitamin B12 binders of serum and does not represent vitamin B12 deficiency, giving no justification for vitamin B12 supplementation in users of OCs.