Recommended daily vitamin D intakes are often insufficient to correct secondary hyperparathyroidism in patients with primary osteoporosis and osteopenia, Canadian researchers report.
“The Osteoporosis Society of Canada recommends that patients with osteoporosis take 800 IU vitamin D daily,” say Edmund Yendt and colleagues from Queens University in Kingston, Ontario.
“At baseline, vitamin D intakes exceeded 800 IU daily in 19% of our patients with secondary hyperparathyroidism, so this dose is clearly inadequate for some patients,” they add.
Yendt and team measured biochemical variables, renal function and calcium and vitamin D intakes in 218 female patients with primary osteoporosis or osteopenia.
At baseline, 75 patients had parathyroid hormone (PTH) levels in the upper sixth of the reference range, indicating hyperparathyroidism. The remaining 143 patients had PTH levels in the rest of the reference range.
Patients were treated with either 1000 IU of vitamin D3 daily or 50 000 IU of vitamin D2 once weekly and followed-up after 1 year. In addition, the researchers followed-up patients with secondary hyperparathyroidism until PTH levels became normal.
In one-third of the hyperparathyroid patients, the standard baseline treatment failed to correct the secondary hyperparathyroidism, the researchers report in the journal Clinical Endocrinology.
Specifically, unusually high doses of vitamin D (50 000 IU vitamin D2 twice weekly) were required to restore serum PTH levels to normal in nine patients with no evidence of celiac disease or other malabsorptive disorders.
There were also six patients whose serum PTH levels only returned to normal when supplemental calcium in the form of calcium carbonate was changed to calcium citrate.
Yendt et al conclude: “Large doses of vitamin D are frequently necessary to suppress secondary hyperparathyroidism in patients with primary osteoporosis and osteopenia. This suggests that vitamin D metabolism may be altered in some of these patients.”