Bone mass and long-term monophasic oral contraceptive treatment in young women

Abstract

A prospective study has been designed to investigate bone metabolism in young women taking an oral monophasic contraceptive formulation (ethinylestradiol 20 micrograms + desogestrel 0.150 mg) over 5 years. Healthy women (n = 200) between 19 and 22 years of age were divided into two groups. Group A received oral contraception, Group B did not receive any treatment. All the subjects underwent a bone mass density (BMD) evaluation at spinal level L2-L4 with Dexa (Norland XR-26) and a measurement of the serum alkaline phosphatase levels and urinary excretion of OH-proline at baseline and every 12 months over 5 years. Our results demonstrated that Group A did not show any significant BMD change after 5 years of oral contraceptive treatment, while Group B demonstrated a significant increase (p < 0.01) in the bone mass content at the end of the time of observation (+7.8% after 5 years). No significant changes were found in serum alkaline phosphatase levels and in urinary excretion of OH-proline at the end of the study in comparison with basal levels in both groups. Our data suggested that long-term treatment with an oral monophasic contraceptive formulation (ethinylestradiol 20 micrograms + desogestrel 0.150 mg) did not modify the BMD but prevented the occurrence of the physiologic peak of bone mass in young women.

PIP: Between June 1988 and March 1989 in Italy, health workers enrolled 200 women aged 19-23 attending obstetric-gynecology clinics in and around Pavia into a five-year study of the effects of an oral contraceptive (OC) with 20 mcg ethinyl estradiol and 0.15 mg desogestrel on bone mass. They were able to follow 76 of the 100 women using the OC and 71 of the 100 women using no OC for five years. Health workers conducted a bone mass density (BMD) evaluation at spinal level L2-L4 with Dexa (Norland XR-26). They measured serum alkaline phosphatase levels and urinary excretion of hydroxyproline (OH-proline) at baseline and every 12 months for five years. Neither urinary excretion of OH-proline levels nor alkaline phosphatase levels differed significantly in the two groups during the five years from baseline levels. Over the five years, the BMD of OC users did not change significantly while the BMD of the controls increased 7.8% from baseline (p 0.01). These findings suggest that this monophasic OC prevented or delayed the physiologic peak bone mass. Even though the low dosage of ethinyl estradiol (20 mcg) may have contributed to the prevention of bone mass loss, it could not achieve the peak bone mass. More studies are needed to understand the effect of long-term OC treatment on bone mineral content.