An open, crossover trial of calcium-fortified milk in prevention of early postmenopausal bone loss

Objective: To establish whether calcium-enriched milk reduces bone loss in women who are within five years of the menopause and have a basal calcium intake less than or equal to 1250 mg. Design: Two-year open, crossover study. Setting: A community-based study carried out in Adelaide, South Australia, between September 1997 and June 2000. Participants: 115 women recruited by newspaper advertisement, who were less than five years postmenopausal, were not taking hormone or other therapy that could affect bone and had a usual calcium intake less than or equal to 1250 mg daily. Intervention: Participants were randomly allocated to Group 1 (who received a supplement of 3 L of calcium-fortified milk weekly in the first year) or Group 2 (who followed their usual diets in the first year). In the second year, Group 1 reverted to their usual diets, and Group 2 received the milk supplement. Main outcome measures: Difference in loss of bone mineral density (BMD) at the spine and forearm in the same individuals on and off the milk supplement; urinary excretion of bone resorption markers in a subset of 72 participants in the first year. Results: With each woman serving as her own control, the rate of bone loss from the spine was 1.76 percentage points less when the women were taking the milk supplement than when they were on their usual diet (95% Cl, 0.54%-2.98%; P = 0.006). However, there was no significant difference in bone loss in the forearm. Fasting urine levels of two markers of bone resorption (hydroxyproline and deoxypyridinoline) were significantly lower in 36 women in the milk group than in 36 women in the usual-diet group (P = 0.03 for both markers). Conclusion: Supplementing the diet with calcium-fortified milk early in the postmenopausal period delays bone loss at the spine but not at the forearm, and reduces the excretion of bone resorption markers.