1. Vitamin D Standardization Program; Havre de Grace MD USA
2. Endocrine Laboratory, Department of Clinical Chemistry; VU University Medical Center; Amsterdam The Netherlands
3. Laboratory of Endocrinology; Academic Medical Center; Amsterdam The Netherlands
4. San Francisco, San Francisco Department of Veterans Affairs Medical Center, Endocrine Research Unit; University of California; San Francisco CA USA
5. Section of Specialized Endocrinology, Department of Endocrinology; Oslo University Hospital, Rikshospitalet; Oslo Norway
6. Faculty of Medicine; University of Oslo; Oslo Norway
7. Department of Chronic Diseases, Metabolism and Ageing; Laboratory of Clinical and Experimental Endocrinology; KU Leuven Belgium
8. Division of Nutritional Sciences; Cornell University; Ithaca NY USA
9. Department of Biochemistry; University of Wisconsin-Madison; Madison WI USA
10. Department of Biomedical and Molecular Sciences; Queen's University; Kingston ON Canada
11. Institute of Endocrinology and Diabetes; The Children's Hospital at Westmead; Sydney NSW Australia
12. Department of Medicine, Endocrinology Division, College of Physicians and Surgeons; Columbia University; New York NY USA
13. Division of Endocrinology; San Raffaele University Hospital; Milan Italy
14. Osteoporosis Clinical Research Program and Institute on Aging; University of Wisconsin-Madison; Madison WI USA