Abstract
BackgroundVitamin D deficiency has long been studied as a risk factor for osteoporosis. However, the association between serum vitamin D status, bone mineral density (BMD) and the incidence of vertebral fractures (OVFs) remain controversial. It is believed that free portion of the circulating vitamin D carries the metabolic activities of vitamin D. Therefore, the aim of the present study is to analyse if free vitamin D correlates with BMD and osteoporotic fragile vertebral fractures in the elderly population.MethodsA total of 90 consecutive patients, including 81 female and 9 male patients, aged > 48 years, were included in this cross sectional study between March and July of 2018. Total vitamin D (total 25(OH)D), free vitamin D (free 25(OH)D), calcium and phosphorus were measured. BMD was measured using dual energy X-ray absorptiometry (DEXA) and osteoporotic vertebral fracture was assessed using plain radiograph. Multiple linear regression was performed to find out the association between total vitamin D, free vitamin D and BMD at various sites. To evaluate the association with osteoporotic vertebral multivariate logistic regression model was used.ResultsThe mean total vitamin D and free vitamin D were 25.1 ± 10.2 and 6.1 ± 1.7 respectively. Free vitamin D had a linear correlation with total vitamin D (R2 = 0.69). While free vitamin D had a positive correlation with lumbar BMD roles (p < 0.05), total vitamin D didn’t have any association with BMD at any site. Of the total patients, 62 patients (68.9%) had thoracolumbar junction OVFs. Free vitamin D level correlated with the prevalence of OVFs as well as lumbar osteoporosis (p < 0.05). However, there was no statistical correlation between serum vitamin D status and the OVFs.ConclusionsFree vitamin D was significantly related to the occurrence of thoracolumbar junction OVFs and lumbar BMD, which assumed to be a positive predictor for fracture and osteoporosis prevention. However, total serum vitamin D levels did not have any association with BMD at different sites as well as fragile vertebral fracture.Trial registrationThe study is registered at clinicaltrials.gov NCT03605173.
Highlights
Vitamin D deficiency has long been studied as a risk factor for osteoporosis
Relationship between Total and free vitamin D When plotted a scattered plot graph (Fig. 1), free vitamin D had a linear correlation with total vitamin D (r = 0.83, 95%CI: 0.76–0.88)
Free vitamin D concentration was found to be lower in 62 patients with Osteoporotic vertebral fracture (OVF) (5.9 ± 1.6 pg/ml) than patients without OVFs (6.8 ± 1.7 pg/ml) (p < 0.05) (Fig. 3)
Summary
The association between serum vitamin D status, bone mineral density (BMD) and the incidence of vertebral fractures (OVFs) remain controversial. Osteoporosis is an inevitable chronic condition that results in the reduction of the bone mineral density and fragility of the bone. It is the predisposing factor for millions of fractures worldwide every year. Vitamin D is a fat-soluble pro-hormone obtained through skin exposure to sunlight and from dietary intake This vitamin is bound to vitamin D-binding protein (DBP) in circulation and undergoes hydroxylation first in the liver and in the kidney to form 25-hydroxy vitamin D (25(OH)D) and active hormone 1,25-dihydroxyvitamin D (1,25(OH)2D) respectively. In clinical practice, measuring serum 25(OH) D concentration is considered to be the best estimation of Vitamin D status [6]
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