Decreased retinol transport proteins in Thai post-menopausal women with osteoporosis

High vitamin A ingestion or high serum retinol have been postulated to increase the risk of fractures and osteoporosis by reduced bone mineral density (BMD). Retinol is carried and transported to the tissues bound to retinol binding protein 4 (RBP4) and transthyretin (TTR). The relationships between retinol, retinol transport protein, retinol binding protein 4 (RBP4) and transthyretin (TTR) and BMD and osteoporosis are unclear. To examine the association between retinol and RBP4 and TTR and osteoporosis, 73 osteoporotic and 71 normal Thai postmenopausal women were studied. RBP4 and retinol levels did not differ between the groups. Serum TTR was significantly higher in control than osteoporotic subjects (89.47 and 144.53 microg/ml, respectively, p = 0.003, Mann-Whitney U test). TTR was positively correlated with BMD at several sites, such as the total radius bone (r = 0.172, p = 0.008, Spearman rank test). Osteoporosis risk was analyzed with binary logistic regression. Lean elderly Thais with lower TTR levels had a higher risk of osteoporosis. RBP4 and retinol levels had no relationship with disease status among Thai post-menopausal women. These results suggest calcium, minerals, vitamins and the retinol transport protein, transthyretin may be involved in the pathogenesis of osteoporosis.