Vitamin D Insufficiency: Disease or No Disease?

• Published in: Journal of bone and mineral research Vol. 23; no. 7; pp. 1052 - 1060
• Main Authors: Hansen, Karen E, Jones, Andrea N, Lindstrom, Mary J, Davis, Lisa A, Engelke, Jean A, Shafer, Martin M
• Format: Journal Article
• Language: English
• Published: Washington, DC John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR) 01.07.2008; American Society for Bone and Mineral Research; Amer Soc Bone & Mineral Res
• Subjects: Biological and medical sciences; Calcium - metabolism; calcium absorption; Female; Fundamental and applied biological sciences. Psychology; Humans; Mass Spectrometry; menopause; Middle Aged; nutrition; Original; Postmenopause; Skeleton and joints; treatment; Vertebrates: osteoarticular system, musculoskeletal system; vitamin D; Vitamin D - metabolism; Vitamin D Deficiency - metabolism; Vitamin D Deficiency - physiopathology; Osteoarticular system; Vertebrata; Absorption; Mammalia; Treatment; Calcium; Nutrition; Vitamin D; Menopause; calcium absorption; Inorganic element
• ISSN: 0884-0431; 1523-4681
• DOI: 10.1359/jbmr.080230

Vitamin D insufficiency (VDI) is widely reported. In patients with normal PTH, the diagnosis rests on increases in fractional calcium absorption (FCA) when 25(OH)D increases above 30 ng/ml. However, estimates of increased FCA after correction of VDI vary dramatically, depending on study methods. We used a dual stable calcium isotope to clarify the impact of vitamin D repletion on FCA in postmenopausal women with VDI. We hypothesized that FCA would increase with vitamin D repletion. We studied postmenopausal women with VDI [25(OH)D = 16–24 ng/ml] and an estimated calcium intake ≤1100 mg daily. Exclusion criteria included hypercalcemia, hypercalciuria, renal insufficiency, nephrolithiasis, gastrointestinal disorders, osteomalacia, prior adult fragility fracture, baseline T‐score < −3.0, and use of medications known to interfere with vitamin D or calcium metabolism. Each woman underwent inpatient FCA studies before and after correction of VDI. We used ergocalciferol 50,000 IU/d for 15 days to achieve vitamin D repletion. During each study, women consumed their typical diet. They ingested 44Ca orally with breakfast and received 42Ca intravenously. We collected urine for 24 h and measured its calcium isotope content by mass spectrometry. Eighteen women completed the study; all but two had normal PTH. During the first and second FCA studies, their mean 25(OH)D level was 22 ± 4 and 64 ± 21 ng/ml, respectively (p < 0.001). Subjects' average FCA was 24 ± 7% initially and 27 ± 6% after vitamin D repletion (p = 0.04). Thus, FCA increased by 3 ± 1% with correction of VDI. Postmenopausal women with VDI experience small FCA increments with vitamin D therapy. In existing literature, this small change in FCA does not associate with lower fracture rates or consistently higher bone mass. Future studies should ascertain whether small FCA increments favorably affect the skeleton.