INTRODUCTION AND AIMS: Bone 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 evaluated the effects of cigarette smoking on BGP levels in patients with end stage renal disease (ESRD).
METHODS: Secondary analysis of the VIKI study, involving 370 hemodialysis patients from 18 dialysis centers in Italy. Study subjects were administered a questionnaire to ascertain smoking status (i.e., current, past, or never smoker). Potential associations of smoking, BGP levels, fractures, and vascular calcifications were evaluated.
RESULTS: Among dialysis patients, smokers had significant lower BGP levels (152 vs. 204 mcg/L, p= 0.003). Smokers also had lower levels of phosphate ([4.25 (3.7, 5.3)] vs. [4.86 (4.0, 5.6)] mg/dl, p= 0.008) and albumin ([3.8 (3.5, 4.0)] vs. [3.9 (3.6, 4.2)] g/dL, p= 0.001). Lower BGP levels were associated with aortic calcification (p<0.001), iliac calcification (p=0.042) and vertebral fractures (p=0.023) (Figure 1). Severe aortic vascular calcifications was significantly associated with lower BGP levels (218 mcg/L vs 165 mcg/L, p=0.002). Stratification by gender showed lower median BGP levels in male smokers [147 mcg/L (83.8, 247)] compared to non smokers [206 mcg/L (97.2, 355.3)], p = 0.0055. No significant differences of BGP levels were found in females: smokers 187 mcg/L (107, 361.9), non smokers: 204 mcg/L (115, 403.3) p = 0.7905. The regression model showed that cigarette smoking patients had a statistically significant reduction of 18% in the median values of BGP (parameter estimate -0,199; p = 0.0105; R2 = 0.53).
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