Elsevier

Bone

Volume 40, Issue 3, March 2007, Pages 716-722
Bone

Associations of vitamin D status with bone mineral density, bone turnover, bone loss and fracture risk in healthy postmenopausal women. The OFELY study

https://doi.org/10.1016/j.bone.2006.09.026Get rights and content

Abstract

Introduction

Vitamin D status is considered as an important determinant of bone health but supplementation trials with vitamin D3 have yielded conflicting results. The aim of this study was to investigate the associations between serum 25-hydroxyvitamin D (25-OH D), bone turnover markers, bone mineral density (BMD), radius bone loss and incidence of fracture in postmenopausal women.

Methods

669 postmenopausal women (mean age: 62.2 years) belonging to a population-based cohort were followed prospectively for a median of 11.2 years. At baseline, 25-OH D levels, BMD, bone turnover markers and clinical risk factors of osteoporosis were assessed. BMD loss at the radius was estimated by annual measurements of BMD and all incident fractures which occurred in 134 women were confirmed by radiographs.

Results

73% and 35% of women had serum 25-OH D levels below 75 and 50 nmol/l which correspond respectively to the median and lowest optimal values recently proposed for fracture prevention. 11% of women had levels below 30 nmol/l. Serum 25-OH D correlated modestly with intact PTH (r2 = 0.023, p < 0.0001), but not with bone turnover markers or BMD at the hip and radius after adjustment for age. When levels of 25-OH D were considered as a continuous variable, there was no significant association between 25-OH D levels and radius BMD loss or fracture risk. After adjustment for age, there was no significant difference in incidence of fracture, BMD, radius BMD loss, bone turnover markers, grip strength and the percentage of fallers in the previous year between women with 25-OH D levels below or above 75, 50 or 30 nmol/l.

Conclusions

In a population of home-dwelling healthy postmenopausal women with few of them with severe vitamin D deficiency, vitamin D status may not be an important determinant of bone health.

Introduction

Vitamin D status has for long been recognized as an important factor for bone health and its contribution has recently received increased attention [1], [2], [3], [4]. From a physiopathological point of view, vitamin D insufficiency, that corresponds to a smaller decrease of 25-hydroxyvitamin D (25-OH D) than vitamin D deficiency, may lead to secondary hyperparathyroidism resulting in higher bone remodeling, bone loss and ultimately increased skeletal fragility. Additionally, vitamin D insufficiency may increase postural instability through increased body sway and muscle weakness and reduced ability to counteract falls further increasing the risk of fracture [5]. However, most of studies which have supported these relationships have been performed in institutionalized subjects or older women of the community presenting with a high prevalence of vitamin D deficiency [6], [7], [8], [9]. Conversely, there are few prospective studies that have examined the relationships between mild vitamin D insufficiency and bone fragility in younger home-dwelling postmenopausal women from whom the majority of fractures arise. Supplementation trials with vitamin D3 in such population using bone loss or fracture incidence as an outcome have yielded conflicting results [3], [4], [10], [11], [12], [13]. Part of this controversy could be attributed to differences in starting levels of 25-OH D levels and/or to difference in the dose of vitamin D levels given as suggested by a recent meta-analysis [14].

The aim of our study was to investigate the associations between serum levels of 25-OH D, bone turnover, BMD and incidence of fracture in healthy postmenopausal women followed prospectively for a median of 11.2 years.

Section snippets

Participants

We investigated the postmenopausal women of the OFELY (“Os des Femmes de Lyon”) cohort, a prospective study of the determinants of bone loss which has been previously described in details [15]. The cohort of this study comprises 1039 Caucasian women 31–89 years of age, including 671 postmenopausal women, recruited between February 1992 and December 1993, from the regional section of a large health insurance company (Mutuelle Génerale de l'Education Nationale, Lyon, France) of the Rhône district

Relationships between serum 25-OH D and serum PTH

Serum 25-OH D levels decreased (r =  0.19, p < 0.0001) whereas intact PTH increased (r = + 0.19, p < 0.001) with age. The relationships between serum 25-OH D levels and PTH were tested using different models and the best fitting curve was obtained with linear regression. As shown on Fig. 1, there was a moderate negative association between serum 25-OH D and serum intact PTH (r =  0.15, p < 0.0001 after adjustment for age) (Fig. 1). Consequently in the subsequent analyses, cut-off values of 25-OH D were

Discussion

In this study, we analyzed the associations between serum 25-OH D levels, bone turnover, BMD, BMD loss and incidence of fracture in a population of healthy postmenopausal women from age 50 to 80 years. Although women with 25-OH D levels below 50 nmol/l or 30 nmol/l had a higher incidence of fracture than the other individuals, this difference disappeared after adjustment for age. No significant age-independent association could be detected between 25-OH D levels and BMD at the hip and forearm,

Acknowledgments

This study was partly supported by a contract INSERM/MSD Chibret (the OFELY study).

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