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Previous Volume 329:1281 October 21, 1993 Number 17 Next

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To the Editor: In our study describing the effects of calcium supplementation on bone loss in normal postmenopausal women (Feb. 18 issue),¹ the bone mineral density of the lumbar spine increased significantly during the first six months in both the placebo and calcium-treated groups. We speculated that this increase was attributable to a change in the software for the bone densitometer between the base-line and six-month visits. Further consultation with the manufacturer confirmed that the new software changed the values for bone mineral density of the lumbar spine. We therefore reanalyzed the earlier scans using the new software. This reanalysis resulted in higher values for bone density at base line in both groups, eliminating the apparent increase between base line and six months in the placebo group (Figure 1). The new mean (±SE) rates of change of bone density in the lumbar spine were -0.0067 ±0.0020 g per square centimeter per year in the placebo group and +0.0017 ±0.0019 g per square centimeter per year in the calcium group (P = 0.003), a greater statistical difference than that reported earlier. The reanalyzed data provide a more realistic description of the changes in bone density with or without calcium supplementation at this important fracture site.

View larger version (14K): [in this window] [in a new window]   Figure 1. Mean (±SE) Lumbar Spinal Bone Mineral Density (BMD) in Postmenopausal Women Given Calcium Supplementation or Placebo for Two Years, Based on Reanalysis of the Base-Line Measurements.

 

Ian R. Reid
University of Auckland School of Medicine
Auckland, New Zealand

References

1. Reid IR, Ames RW, Evans MC, Gamble GD, Sharpe SJ. Effect of calcium supplementation on bone loss in postmenopausal women. N Engl J Med 1993;328:460-464. [Free Full Text]

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