Available high- quality RCTs did not support a beneficial effect of cholecalciferol on systemic IL-6 and CRP .
Plasma 1,25(OH)2D levels decrease in postmenopausal women with hypovitaminosis D.
OBJECTIVE Although calcitriol ( 1,25(OH)2D ) is considered the biologically active vitamin D metabolite , several studies have shown that calcidiol ( 25OHD ) is the vitamin D metabolite that is most closely linked to parathyroid function and indices of calcium homeostasis . Moreover , low levels of 25OHD have been associated with increased risk of different diseases including cancer , diabetes , and myopathy . DESIGN Cross-sectional study . METHODS We studied relations between  plasma concentrations of 25OHD , 1,25(OH)2D , and parathyroid hormone ( PTH ) in fasting plasma sample s from 315 healthy postmenopausal women r and omly selected from the local background population . RESULTS P-1,25(OH)2D levels varied in a concentration-dependent manner with P-25OHD levels ( P<0.001 ) . Thus , P-1,25(OH)2D levels were the lowest in women with vitamin D insufficiency , i.e. , P-1,25(OH)2D levels were reduced by approximately one-third in subjects with P-25OHD levels below 25 nmol/l compared with levels above 80 nmol/l ( P<0.01 ) . The association was most pronounced at P-25OHD concentrations below 80 nmol/l , whereas no major increase in P-1,25(OH)2D was observed at P-25OHD concentrations above 80 nmol/l . In multiple regression analysis , PTH was a minor although significant predictor of P-1,25(OH)2D levels . CONCLUSIONS In normal postmenopausal women , the conversion of 25OHD to active vitamin D depends on the substrate concentration . Our data support that vitamin D insufficiency should be considered at P-25OHD levels below 80 nmol/l
Available high- quality RCTs did not support a beneficial effect of cholecalciferol on systemic IL-6 and CRP .