Influence of Obesity on Vertebral Fracture Prevalence and Vitamin D Status in Postmenopausal Women

A. El Maghraoui; S. Sadni; A. El Maataoui; A. Majjad; A. Rezqi; Z. Ouzzif; A. Mounach

Disclosures

Nutr Metab. 2015;12(44) 

In This Article

Methods

Subjects

This was a cross-sectional study conducted from June 2012 to June 2014 that enrolled menopausal women 50 years old and over, living in the region of Rabat. Participants were recruited from a variety of sources including advertisements, "word of mouth", clinician referrals, or from local hospital staff families. General exclusion criteria were previous diagnosis of osteoporosis, non-Caucasian origin and diseases, drugs, and other major determinants known to affect bone metabolism. Thus, we excluded subjects with gastrectomy, intestinal resection, recent hyperthyroidism or hyperparathyroidism, recent severe immobilization or treatment with corticosteroids (more than 3 months). Our institutional review board approved this study. The procedures of the study were in accordance with the Declaration of Helsinki, and formal ethics committee approval was obtained for the study. Data from four hundred and twenty nine were collected. All the participants gave an informed and written consent. Each subject completed a standardized questionnaire designed to document putative risk factors of osteoporosis. History of fractures, lifestyle (alcohol consumption, gymnastics or jogging/walking, smoking) and diet (milk, yogurt, cSSheese) habits were also recorded. The women were asked whether they usually drank milk, coffee, or alcohol, if they ate cheese or yogurt, if they did gymnastics or jogging/walking, and if they smoked tobacco. Dairy products intake was then arbitrarily classified as low (mean calcium intake <600 mg/day), normal (mean calcium intake > 600 mg/day and ≤ 1000 mg/day), and high (≥1000 mg/day). Physical activity was classified as low if the women walked < 3 h/week, normal (walking time ≥ 3 h/week and <6 h/week), and high (≥ 6 h/week). Menstrual and reproductive history were assessed: all patients were menopausal since at least one year. Height and weight were measured in our centre before DXA measurement, in light indoor clothes without shoes. Body mass index (BMI)] was calculated by dividing weight in kilograms by height in meters squared.

BMD Measurement

Bone mineral density was determined by a Lunar Prodigy Vision DXA system (GE-Lunar Corp., Madison, WI). The DXA scans were obtained by standard procedures supplied by the manufacturer for scanning and analysis. All BMD measurements were carried out by 2 experienced technicians. Daily quality control was carried out by measurement of a Lunar phantom. At the time of the study, phantom measurements showed stable results. The phantom precision expressed as the coefficient of variation percentage was 0.08. Moreover, reproducibility has been assessed in clinical practice and showed a smallest detectable difference of 0.040 g/cm2 (spine) and 0.021 (total hips).[18,19] Patient BMD was measured at the lumbar spine (anteroposterior projection at L1-L4) and at the hip (i.e., femoral neck, trochanter, and total hip). Using the Moroccan female normative data,[20] the World Health Organization (WHO) classification system was applied, defining osteoporosis as T-score ≤ −2.5 and osteopenia as −2.5 < T-score < −1. Study participants were categorized by the lowest T-score of the L1–4 lumbar spine, femur neck, or total femur.

Vertebral Fracture Assessment (VFA)

VFA was classified using a combination of Genant semiquantitative (SQ) approach and morphometry in the following manner: each VFA image was inspected visually by one clinician (AM) who is an experienced reader of VFA which was blinded to clinical data, to decide whether it contained a fracture in any of the visualized vertebrae and assigned a grade based on Genant SQ scale,[21] where grade 1 (mild) fracture is a reduction in vertebral height of 20–25 %, grade 2 (moderate) a reduction of 26–40 %, and grade 3 (severe) a reduction of over 40 %. In case of doubt regarding fracture grade, the vertebrae in question was measured using built-in morphometry. Automatic vertebral recognition by the software was used. Positioning of the six morphometry points was modified only when the software failed to correctly recognize vertebral heights. Subjects with no fractures were included in the non-fracture group, whereas those with grade1 or higher fractures were included in the fracture group. However, as many studies rarely report mild deformities as "fractures", and to realize comparisons with the literature, we performed a double analysis including and excluding grade 1 fractures from the fracture group.

Laboratory Evaluation

All blood samples were collected under fasting conditions on the same day of acquisition of the VFA images, between 8 and 10 a.m., stored at −20 °C, and analyzed at the same time. The serum concentration of 25-hydroxivitamin D (25 (OH) D) was measured using electrochimiluminescence on ELECSYS 2010 analyser (Roche Diagnostics, Mannheim). The intra and inter-assay variation coefficients in our laboratory were 10.5 % and 17.8 %, respectively. In the present study, 25 (OH) D values of ≤ 20 ng/ml were defined as vitamin D insufficiency and of ≤ 10 ng/ml as vitamin D deficiency.

Statistical Analysis

Results are presented as means (SD) and categorical variables are expressed as frequencies. To compare women according to their BMI, women with normal weight, overweight and obesity, chi-square test and analysis of variance ANOVA were used firstly. Women with grade 1 vertebral deformities, women with grade 2/3 VFs and women without VFs were also compared using chi-square test and analysis of variance ANOVA. We performed pairwise comparisons among the 3 groups using the Bonferoni test. Significant risk factors in the univariate analysis for osteoporosis and VFs were entered to a stepwise conditional binary regression analysis and the resulted odds ratios with 95 % confidence intervals were reported. The level for significance was taken as p ≤ 0.05. Excel 2010 and SPSS 20.0 were used for statistical analysis.

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