Cigarette smoking is associated with decreased Bone Gla-protein (BGP) levels in hemodialysis patients

Bone gamma-carboxyglutamic acid (Gla)-protein (BGP or osteocalcin) is a vitamin K-dependent protein involved in the regulation of bone mineralization. Smoking is a risk factor for osteoporosis. We carried out a secondary analysis of the vitamin K Italian (VIKI) study to investigate the association between cigarette smoking and BGP levels in patients with end-stage renal disease. Data were collected in 370 haemodialysis patients, 37% (136) smokers (or ex-smokers) and 63% (234) non-smokers. Vascular calcifications and vertebral fractures (quantitative morphometry) were identified on spine radiographs. Smokers had significantly lower BGP levels (152 vs 204 μg/L, p= 0.003). Smokers had lower plasma phosphate levels (4.2 vs 4.7 mg/dl, p<0.01). Lower BGP levels were associated with aortic calcification (p<0.001), iliac calcification (p=0.042) and vertebral fractures (p=0.023). In addition, the regression model showed that smoking is associated with a significant reduction of total BGP levels by about 18% (p=0.01). This is the first clinical study in a haemodialysis population, which identifies cigarette smoking as a potential factor that can lower BGP levels, a protective agent in bone and vascular health.