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: One year intervention

Setting: General community

Subjects: Healthy women (n = 154) young (18-30 yr old), with a dietary calcium intake of less than 800 mg/day, and 135 completed the trial.

Intervention: Random assignment to one of three diet intervention groups: 1) control, continue established (< 800 mg/day) dietary intake; 2) medium dairy, increase calcium intake to approximately 1000-1100 mg/day; 3) high dairy, increase calcium intake to approximately 1200-1300 mg/day. Randomization was stratified by OCP use.

Main Outcome Measures: Total body bone mineral density (BMD) and content (BMC); total hip BMD, BMC and bone area; spine BMD, BMC and bone area.

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

Conclusion: Dairy product intake, at levels 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.