Adding Phosphorus to Osteoporosis Drug Treatment

National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), Office of Dietary Supplements (ODS)

Osteoporosis causes bones to weaken and break more easily. Calcium and phosphorus are two minerals that are essential for normal bone formation. Unfortunately, calcium salts commonly prescribed in anti-osteoporosis treatment bind phosphorus from food and restrict phosphorus available for bone building. Teriparatide is a drug that reduces the risk of fractures by increasing bone thickness and strength. Vitamin D is also necessary for strong bones and teeth. The purpose of this study is to evaluate the bone-building effectiveness of two calcium supplements, one with a source of phosphorus and one without, in combination with teriparatide and vitamin D in women with osteoporosis.

Osteoporosis is the most common type of bone disease. Calcium supplements normally used in anti-osteoporosis treatment are calcium salts of carbonate or citrate; however, these salts bind phosphorus from food in the intestine and restrict phosphorus available for bone building. This study will evaluate the efficacy of adding calcium phosphate to a regimen of teriparatide and vitamin D in increasing bone mineral density in women with osteoporosis. It is hypothesized that the group taking the phosphate-containing calcium supplement will have greater gains in bone mineral density (BMD) during the course of the study than the group not receiving phosphate. All participants will receive teriparatide and vitamin D during the course of the 12-month study. Participants will be randomly assigned to one of two groups. One group will receive calcium phosphate and the other will receive calcium carbonate. BMD will be measured at spine and hip at baseline and at 3, 6, and 12 months of treatment.

Participants will receive teriparatide and vitamin D during the course of the 12-month study. They will also receive calcium phosphate.

Participants will receive teriparatide and vitamin D during the course of the 12-month study. They will also receive calcium carbonate.

Participants will receive teriparatide and vitamin D during the course of the 12-month study. They will also receive calcium carbonate.

Participants will receive teriparatide and vitamin D during the course of the 12-month study. They will also receive calcium phosphate.

Bone mineral density (BMD, measured by dual X-ray absorptiometry - DEXA) measured at several intervals during the study. BMD measured as grams per square centimeter (g/cm2).

The principle outcome measure was change in bone mineral density (BMD) under treatment with an anabolic agent (teriparatide).

Change From Baseline in Urinary Calcium to Creatinine Ratio, Urinary Phosphorus to Creatinine Ratio at 12 Months

Inclusion Criteria: Bone mineral density (BMD) T-score less than -1.0 One or more vertebral fractures Serum creatinine less than 1.3 mg/dL Serum phosphorus less than 3.6 mg/dL Daily phosphorus intake below NHANES-III median Body mass index (BMI) less than 30 kg/m2 Exclusion Criteria: Paget's disease or history of osteosarcoma Systemic corticosteroid therapy Hyperparathyroidism Recent history of kidney stone Anticonvulsant therapy known to alter vitamin D metabolism Radiation therapy to bone

Heaney RP, Recker RR, Watson P, Lappe JM. Phosphate and carbonate salts of calcium support robust bone building in osteoporosis. Am J Clin Nutr. 2010 Jul;92(1):101-5. doi: 10.3945/ajcn.2009.29085. Epub 2010 May 19.

Heaney RP, Watson P. Variability in the measured response of bone to teriparatide. Osteoporos Int. 2011 Jun;22(6):1703-8. doi: 10.1007/s00198-010-1376-1. Epub 2010 Sep 9.