The influence of a monophasic sub-50 oral contraceptive (OC), Marvelon, on fasting total homocysteine levels was investigated in OC users and controls. Homocysteine levels in serum of OC users were significantly higher (P less than .01) than in controls during the low-hormonal phase of the cycles and comparable with levels determined in heterozygotes for homocystinuria. Blood levels of pyridoxal phosphate (PLP) were significantly lower (P less than .05) in OC users both in the low and high hormonal phase. However, there were no significant differences in the levels of homocysteine nor in folate and vitamin B12 between both groups in the high-hormonal phase. In contrast to the control group, the homocysteine levels in OC users in the high-hormonal phase of the cycle were significantly decreased compared with those on a low-hormonal day (P less than .05). These data suggest that cyclically recurrent periods of hyperhomocysteinemia do occur during sub-50 OC use in normal women and might be considered a predisposition to the occurrence of vascular complications.
PIP: Serum level of the amino acid homocysteine, and vitamins folate, B12 and pyridoxal phosphate, and red blood cell folate levels were determined on Cycle days 3 and 21 in 26 women using the oral contraceptive Marvelon (30 mcg ethinyl estradiol and 150 mcg desogestrel), compared with 15 menstruating women. The 26 pill users had taken Marvelon for mean 3.7 years. Fasting homocysteine was assayed with an amino acid autoanalyzer; folate and B12 by radioimmunoassay; pyridoxal by high-performance liquid chromatography. The pill users had significantly higher homocysteine on Day 3 than controls (p0.01), levels comparable to those in heterozygote carriers of homocystinuria. Homocysteine levels were significantly lower in pill users on Day 21 compared to their levels on Day 3. Pyridoxal levels were significantly lower in Marvelon users on both days tested (p0.05). Homocysteine, folate and B12 were not significantly different in pill users and non-users on Day 21. The data indicate a cycle of high and low homocysteine levels in users of Marvelon. High homocysteine has been implicated in vascular disease, and may be a causative factor in the risk for thrombosis in pill users.