Dietary Calcium Intake Protects Women Consuming Oral Contraceptives from Spine and Hip Bone Loss

Context: It is estimated that 80% of all women have used oral contraceptives (OCP), but OCP use may prevent attainment of maximal peak bone mass in young women and thus increase the risk of osteoporosis later in life.

Objective: This study examined whether increased calcium intake could reduce the detrimental effects of OCP use on bone mass in young women.

Design: The study design was a 1-yr intervention.

Setting: The study was performed in a general community setting.

Subjects: One hundred fifty-four young (18-30 yr old) healthy women with a dietary calcium intake of less than 800 mg/d began the study, and 135 completed the trial.

Intervention: Subjects were randomly assigned to one of three diet intervention groups: 1) control, continuous established (<800 mg/d) dietary calcium intake; 2) medium dairy, increase calcium intake to approximately 1000-1100 mg/d; and 3) high dairy, increase calcium intake to approximately 1200-1300 mg/d. Randomization was stratified by OCP use.

Main Outcome Measures: The main outcome measures were total body bone mineral density (BMD) and content (BMC); total hip BMD, BMC, and bone area; and spine BMD, BMC, and bone area.

Results: Dairy product intervention positively impacted the percentage change in total hip BMD and BMC. In addition, dairy product intake prevented a negative percentage change in total hip and spine BMD in OCP users.

Conclusion: Dairy product intake, at levels necessary to achieve the recommended intakes of calcium, protected the total hip BMD and spine BMD from loss observed in young healthy women with low calcium intakes who were using OCP.