Effects of contraceptive use on bone biochemical markers in young women

The purpose of this study was to compare biochemical markers of bone resorption and formation in young women using different hormonal contraceptive methods. Women aged 18-39 yr who were using depot medroxyprogesterone acetate (DMPA) contraception were recruited for the study; comparison women were matched by age and clinic location. There were 116 women using DMPA, 39 using oral contraceptives containing estrogen and progestin, and 72 not currently using hormonal contraceptives. Biochemical measurements were serum calcium, PTH and osteocalcin, and urine N-telopeptide. Bone density was measured using dual-energy x-ray absorptiometry. The N-telopeptide levels, adjusted for age and other risk factors, were 42.4 +/- 2.3 nmol/mmol creatinine in the DMPA group, 26.2 +/- 3.3 nmol/mmol in the oral contraceptive group, and 35.4 +/- 2.9 nmol/mmol in the nonusers; significant differences were seen in all pairwise comparisons. Osteocalcin levels showed the same pattern, although the difference between the DMPA users and nonusers was not statistically significant. There were no differences among groups in the PTH levels. The bone density at the spine was 1.086 +/- 0.085 g/cm(2) in the DMPA group, 1.103 +/- 0.095 g/cm(2) in the oral contraceptive group, and 1.093 +/- 0.090 g/cm(2) in nonusers (P = 0.051). The results suggest that in women using DMPA bone resorption exceeded bone formation.