Vitamin D status and sex hormone binding globulin: Determinants of bone turnover and bone mineral density in elderly women

Authors

  • Marcel E. Ooms,

    Corresponding author
    1. Institute for Research in Extramural Medicine (EMGO-Institute) Vrije Universiteit, Amsterdam, The Netherlands
    • EMGO-Institute Medical Faculty of the Vrije Universiteit Van der Boechorststraat 7 1081 BT Amsterdam, The Netherlands
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  • Paul Lips,

    1. Institute for Research in Extramural Medicine (EMGO-Institute) Vrije Universiteit, Amsterdam, The Netherlands
    2. Department of Endocrinology, Free University Hospital, Amsterdam, The Netherlands
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  • Jan C. Roos,

    1. Department of Nuclear Medicine, Free University Hospital, Amsterdam, The Netherlands
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  • Wim J. F. van der Vijgh,

    1. Clinical Research Laboratory, Free University Hospital, Amsterdam, The Netherlands
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  • Corrie Popp-Snijders,

    1. Endocrinological Laboratory, Free University Hospital, Amsterdam, The Netherlands
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  • P. Dick Bezemer,

    1. Department of Epidemiology and Biostatistics, Vrije Universiteit, Amsterdam, The Netherlands
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  • Lex M. Bouter

    1. Institute for Research in Extramural Medicine (EMGO-Institute) Vrije Universiteit, Amsterdam, The Netherlands
    2. Department of Epidemiology and Biostatistics, Vrije Universiteit, Amsterdam, The Netherlands
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Abstract

To examine the relation of the vitamin D status and the remaining estrogen activity with bone turnover and bone mineral density (BMD) in elderly women, BMD was measured at both hips using dual-energy X-ray absorptiometry and at the distal radius using single photon absorptiometry, in 330 healthy women aged 70 and over. Vitamin D metabolites, sex hormone binding globulin (SHBG), PTH(1–84), osteocalcin, alkaline phosphatase, and hydroxyproline and calcium excretion in 2 h fasting urine were measured. Multiple linear regression was used to adjust for potential confounders. In 65% of the women, serum 25(OH)D was below 30 nmol/l. Only values below a threshold for 25(OH)D were negatively related to serum PTH(1–84) (p = 0.02, threshold at 25 nmol/l) and to osteocalcin levels (p = 0.04, threshold at 30 nmol/l). BMD of the femoral neck and trochanter was positively related to serum 25(OH)D (left neck p = 0.001) with thresholds at 30 nmol/l whereas the distal radius was not (p = 0.32). Serum PTH was negatively related to BMD at all measurement sites (all p < 0.001). Serum SHBG, an inverse measure of estrogen activity, was positively related to osteocalcin levels (p = 0.004) and the urinary hydroxyproline/creatinine ratio (p = 0.002) and negatively related to the BMD of the trochanter (left trochanter p = 0.02) and the distal radius (p = 0.001). We conclude that in elderly women, serum 25(OH)D levels below 30 nmol/l are associated with secondary hyperparathyroidism and increased bone turnover. SHBG is positively related to bone turnover. Vitamin D deficiency especially influences BMD of the femoral neck, a cortical area. SHBG mainly influences BMD at the trochanteric region and distal radius, predominantly trabecular areas, which may reflect the effects of remaining estrogen activity.

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