The authors are indebted to Dr Heaney for noting this important secondary result of our study. The lack of response in the calcium-only group of the trial, both in regard to parathyroid hormone (PTH) and bone resorption, is indeed significant.

Our results indicate that in severely vitamin D-deficient elderly subjects, bone loss cannot be prevented by only raising calcium intake from 600–700 (baseline) to 1200 mg per day. On the other hand, vitamin D repletion above the midpoint of the reference range of 25-hydroxyvitamin D serum concentrations, together with an increased calcium intake of 1200 mg per day, was successful in achieving a significant decrease in bone resorption and PTH levels in our trial.

According to findings described in Dr Heaney's letter and our results, calcium is more efficacious in conjunction with vitamin D. This is particularly important to elderly patients, who have a high rate of vitamin D deficiency.