LAUSR

SummaryWe aimed to determine whether the effect of calcium supplements on bone metabolism is modified by physical activity (PA) through a subgroup analysis of an RCT. PA may be a favorable effect modifier of the association between calcium intake and bone loss in perimenopausal and postmenopausal women.PurposePhysical exercise can potentially modify bone metabolism. Here we aimed to determine whether the effect of calcium supplements on bone metabolism is modified by physical activity (PA) through a subgroup analysis of a randomized, double-blind, placebo-controlled trial.MethodsThe trial was conducted over the course of 2 years, and participants were 450 healthy women between 50 and 75 years of age who were randomly assigned to three equally-sized (N = 150 each) groups (500 mg calcium, 250 mg calcium, and placebo). Levels of PA at baseline were evaluated by quantifying moderate (4 METs) and vigorous (6 METs) activities based on a 7-day activity recall, and the total MET-hours per week was calculated. Follow-up BMD examinations were conducted 2 years later. Two-year changes in BMD were compared between the intention-to-treat higher PA subgroup (≥ 10 MET-hours/week) and the lower PA subgroup (< 10 MET-hours/week).ResultsOf the 450 participants, 418 underwent follow-up BMD measurements. Regarding the lower PA subgroup, spinal BMD in the 500 mg/day calcium supplement group decreased significantly less (− 0.029 g/cm2, P = 0.042) than in the placebo group (− 0.045 g/cm2), and femoral neck BMD in the 500 mg/day calcium supplement group decreased significantly less (− 0.027 g/cm2, P = 0.049) than in the placebo group (− 0.038 g/cm2). In contrast, changes in neither spinal nor femoral neck BMD significantly differed between the three treatment groups in the higher PA subgroup.ConclusionsPA is a favorable effect modifier of the association between calcium intake and bone loss in perimenopausal and postmenopausal women with low calcium intake.Clinical trials registry numberUMIN000001176