Background/Purpose:

Current smoking is a known risk factor for loss of bone mineral density (BMD), and is part of the FRAX ™ 10-year fracture risk stratification tool developed by the World Health Organisation (1).

Reduction in BMD due to smoking seems to be more in men than women, but far less data exists looking at the effects of smoking on BMD in males. The site of maximal bone loss has not been clearly identified, varying between the hip and lumbar spine in different studies in a recent review of three meta-analyses (2). There could also be a potentially confounder in abdominal aortic calcification due to atherosclerosis falsely increasing the lumbar spine BMD (3).  This study aimed to establish the anatomical area of maximal BMD reduction due to smoking and to examine the differential impact in each gender.

Methods:

Data was analysed from male and female patients having dual-energy X-ray absorptiometry (DEXA) assessment between 2004 and 2011. Patients were categorised as never-smoked, current smokers, and previous smokers. Student’s t-test was performed to identify whether differences existed between smokers and non-smokers by gender. Logistic models, adjusting for age and body mass index (BMI) were then fitted examining the odds of a low bone density in both sites by gender. Finally the odds of being diagnosed as having osteoporosis (OP) (T score <-.25 at either spine or hip) was ascertained using logistic regression.

Results:

25,904 patients were included in the study, of which 3,136 were ex-smokers and 2,224 were current smokers.  This included 3901 males (15%). Mean age at scan in the whole cohort was 62.6 years (SD12.6). Current smokers were more likely to be male 398/1826 vs 3503/20169 (17.9% vs 14.8% P <0.001).  Using Student’s t-test, the BMD in women was not significantly different in the lumber spine (1.06g/cm2 vs 1.05 g/cm2 p=NS) but was significantly reduced in the hip (0.84 vs 0.85 P =0.004). In men, despite the lower numbers both spine and hip BMD were significantly lower (1.08 vs 1.13 p <0.001 and 0.88 vs 0.90 p=0.02). In females, after adjustment for age at scan and BMI the odds of a low BMD in the lumbar spine were higher than the odds in the femoral neck when adjusted for age and BMI (0.54 95%CI 0.41, 0.73 vs 0.38 95%CI 0.24, 0.60 respectively) indicating more loss in the femoral neck. In men the effect was also greater in the femoral neck (OR 0.45 95%CI 0.25, 0.81 in the lumbar spine vs 0.25 95%CI 0.10 0.66 in the femoral neck). The odds of OP in female smokers was 2.13 (95%CI 1.93,2.35) and in male smokers it was 3.17 (95%CI 2.56,3.92).

Conclusion:

Smoking causes significant BMD loss at both the spine and the hip but the effect appears to be more pronounced in male smokers. Abdominal aortic calcification appears to have a minor impact on assessing BMD in the lumbar spine. 

1.   http://www.shef.ac.uk/FRAX/index.aspx

2.  Wong P.K.K. et al “The effects of smoking on bone health.” Clinical Science. 2007; 113: 233-241

3.  Zhu D.X. et al “Mechanisms and clinical consequences of vascular calcification.” Frontiers in Endocrinology. 2012; 3(95): 1-12

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-differential-effect-of-smoking-on-bone-mineral-density-at-the-lumbar-spine-and-neck-of-femur-in-each-gender-an-observational-study/