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  • Title: Oral contraceptives and the cobalamin (vitamin B12) metabolism.
    Author: Hjelt K, Brynskov J, Hippe E, Lundström P, Munck O.
    Journal: Acta Obstet Gynecol Scand; 1985; 64(1):59-63. PubMed ID: 3976378.
    Abstract:
    The mean concentrations of serum (S)-cobalamin (vitamin B12) and S-unsaturated B12 binding capacity (UBBC) were significantly decreased in 101 women (mean age: 30.4 years) taking oral contraceptives (OC) of the combination type, compared to 113 controls. OC users more frequently showed decreased concentrations of S-cobalamin (less than 200 pmol/l) than did their controls. However, the incidence of particularly low concentrations (less than 150 pmol/l) in OC users was not increased. To study a possible dose-dependent effect, 27 women (mean age: 50.5 years) given high-dose estrogen preparations (1-4 mg estrogen) were compared with 31 controls. The two groups showed no difference with regard to S-cobalamin, but the mean S- and plasma-UBBC levels were significantly decreased in the high-dose estrogen group. 12 OC users with decreased S-cobalamin (less than 200 pmol/l), 9 OC users with normal S-cobalamin and 10 controls were studied more intensively. The mean hemoglobin concentration was significantly decreased in those OC users having decreased S-cobalamin. On the contrary, the absorption and excretion of radiolabeled cobalamin and the concentrations of erythrocyte-folate, S-iron and -transferrin did not show any difference between the groups, and all results were normal, by and large. No characteristic changes in plasma volume were found. It is concluded that routine measurement of S-cobalamin in women taking OC is not justified. This study investigated the incidence and etiology of cobalamin (vitamin B12) deficiency in oral contraceptive (OC) users. Mean concentrations of serum (S)-cobalamin and S-unsaturated B12 binding capacity were significantly decreased in 101 women who had been taking combination OCs with an estrogen content of 50 mcg for at least the past 6 months compared to 113 controls who had not used OCs for at least the past 6 months. However, the incidence of particularly low concentrations of S-cobalamin (under 150 pmol/1) was not increased in OC users. To investigate the possibility of a dose-dependent effect, 27 women who wrere using high-dose estrogen OCs with an estrogen content of 1-4 mg were compared with 31 controls who had not used sex steroids. Although the group showed no difference in terms of S-cobalamin concentrations, mean serum and plasma-unsaturated B12 binding capacity levels were significantly decreased in the high-dose estrogen group. When 12 OC users with decreased S-cobalamin (under 200 pmol/1), 9 OC users with normal S-cobalamin, and 10 controls were studied more extensively, the mean hemoglobin concentration was found to be significantly decreased in OC users with decreased S-cobalamin levels. The absorption and excretion of radiolabeled cobalamin and concentrations of erythrocyte-folate, S-iron, and S-transferrin remained normal in all 3 groups and no changes in plasma volume were observed. it is concluded that the decreased S-cobalamin levels found in OC users are caused by a decreased S-unsaturated vitamin B12 binding capacity, possibly reflecting a lowering of the white blood cell count. Routine measurement of S-cobalamin in OC users is not recommended.
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