Elsevier

Bone

Volume 45, Issue 3, September 2009, Pages 423-426
Bone

25-hydroxy vitamin D levels in healthy premenopausal women: Association with bone turnover markers and bone mineral density

https://doi.org/10.1016/j.bone.2009.05.012Get rights and content

Abstract

Background

Vitamin D deficiency is very common in elderly people while there are very few reports on its incidence, determinants and metabolic consequences in young subjects.

Results

In 608 young healthy premenopausal women participating in the BONTURNO study, levels of 25-hydroxyvitamin D [25(OH)D] below 20 ng/ml were found in almost a third of the women. Its levels were inversely (P < 0.001) related with age and body mass index (BMI kg/m2) and directly with sunlight exposure during the summer time, and latitude: i.e. the higher the latitude over Italy, the higher the 25(OH)D level. In women on contraceptive pill the mean 25(OH)D level was significantly increased even when the data were adjusted for age, BMI and sun exposure.

25(OH)D levels, adjusted for age and BMI, were significantly and positively related with serum C-telopeptide of type 1 collagen, serum phosphate and spine bone mineral density (BMD) and negatively with serum PTH, serum magnesium, serum bone alkaline phosphatase (bone AP).

Conclusion

Vitamin D deficiency is rather common in young otherwise healthy Italian women and particularly among those living in the Southern part of the country. The most close determinants of vitamin D deficiency were BMI and sunlight exposure. Vitamin D insufficiency is associated with low spine BMD and increased bone AP even in young individuals.

Introduction

Vitamin D deficiency is very common in elderly people [1] and is associated with an increased risk of falls and fragility fractures [2]. Its incidence is particularly high in southern European countries [3], [4]. Most of the epidemiogical studies have been performed in elderly persons, who are more likely to be affected by the advocated explanations for vitamin D deficiency, i.e. low dietary vitamin D intake and inadequate skin production of the vitamin [1].

The optimal serum concentration of 25-hydroxyvitamin D [25(OH)D] is generally defined as the concentration that maximally suppresses the serum parathyroid hormone (PTH). This is a useful criterion, but PTH may also fluctuate according to dietary calcium intake [5], [6] and renal function [7] which again are more likely to be inadequate in the elderly than in young individuals.

In few studies 25(OH)D levels were found to be correlated with bone mineral density (BMD) but most of these reports were from elderly patients [8], [9], [10], [11].

A negative correlation between 25(OH) D levels and bone turnover markers has been reported in a number of studies including mostly elderly individuals [4], [12], [13], [14], [15], [16].

The BONTURNO study [17] was designed to establish standard values for bone turnover markers, their relationship with BMD and their main determinants in young healthy premenopausal women. Here we describe the distribution and main determinants of 25(OH)D levels in this cohort of young women. We also determined whether there is an association between 25(OH)D levels and BMD or bone turnover markers in healthy young women.

Section snippets

Methods

The inclusion criteria of the women participating in the BONTURNO study, their baseline characteristics and the study procedures are described in detail elsewhere [17].

Briefly, healthy subjects with regular monthly cyclic menses were enrolled from 20 different sites uniformly distributed across Italy. Each centre was asked to recruit 5 healthy individuals for each 5 year age range from 20 to 49. Most volunteers were from the hospital staff or their relatives. Subjects with abnormal laboratory

Results

The main clinical characteristics of the entire study population and according to 25(OH)D levels lower or higher than 20 ng/ml, are listed in Table 1. The distribution frequencies for various 25(OH)D cut-off levels are listed in Table 2. 25(OH)D levels lower than 20 ng/ml were found in almost a third of the women and these women differ significantly from the other for a number of aspects such as sun exposure, physical activity and BMI (Table 1).

The 25(OH)D levels had to be logarithmically

Discussion

Vitamin D deficiency or insufficiency is very common among elderly subjects particularly from Southern European countries. In this study we found that vitamin D insufficiency, as defined by 25(OH)D levels lower than 20 ng/ml, is also common among otherwise healthy young women, accounting for a third of the cohort. The study population was made mostly by hospital staff, which might not be fully representative of the general population, even though we cannot predict in what direction they might

Conflict of interest

S.A. receives consultancy honoraria from MSD and Servier.

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