Five years after completion of a randomised placebo-controlled trial of calcium supplements, there was no effect of calcium on total fracture incidence, a significant reduction in vertebral and forearm fractures and, in a subset, no effect on bone density. There was no increased risk of cardiovascular events after discontinuation of calcium.
Introduction: The Auckland calcium study was a 5-year randomised controlled trial of 1 g/day calcium citrate in 1,471 postmenopausal women. Calcium did not reduce total, vertebral or forearm fracture incidence, increased hip fracture incidence and had beneficial effects on bone mineral density (BMD). A secondary analysis raised concerns about the cardiovascular safety of calcium. The purpose of this study was to determine whether the effects of calcium on fracture incidence, BMD and cardiovascular endpoints persisted after supplement discontinuation.
Methods: Approximately 5-years post-trial, we collected information on the 1,408 participants alive at trial completion from the national databases of hospital admissions and deaths. We contacted 1,174 women by phone, and from these we obtained information on medical events and post-trial calcium use. We undertook BMD measurements at 10 years in a selected subset of 194 women who took study medication for 5 years in the original trial, and did not take bone-active medications post-trial.
Results: Over the 10-year period, there was no effect on total fracture (HR 0.90, 95% CI 0.75-1.07) or hip fracture incidence (1.40, 0.89-2.21), but significant reductions in forearm (0.62, 0.43-0.89) and vertebral fractures (0.52, 0.32-0.85) in those assigned to calcium. There were no between-group differences in BMD at 10 years at any site. The adverse cardiovascular outcomes observed in the 5-year trial did not persist post-trial.
Conclusion: Calcium supplementation for 5 years had no effect on total fracture incidence at 10 years. The positive benefits on BMD and the adverse cardiovascular effects did not persist once supplements were stopped.