Elsevier

Bone

Volume 40, Issue 2, February 2007, Pages 493-497
Bone

Low bone mineral density is related to severity of chronic obstructive pulmonary disease

https://doi.org/10.1016/j.bone.2006.09.005Get rights and content

Abstract

Chronic obstructive pulmonary disease (COPD) appears to be associated with low bone mineral density (BMD). BMD loss can be accelerated by a number of factors associated with COPD, but it is not known whether COPD itself has a direct effect. Our aim was to investigate in a cross-sectional study whether COPD patients have lower BMD than healthy individuals, and whether the severity of the disease affects BMD. Eighty-eight COPD patients attending a rehabilitation program were classified into stages II, III and IV using GOLD criteria. BMD was measured by dual X-ray absorptiometry in lumbar spine (L2–4), femoral neck (FN) and total body (TB). Values were converted to Z-scores (adjusted for age and sex). Associations between Z-scores and steroid use, body mass index, pack-years and six-min walking distance were analyzed.

The Z-scores (mean and (CI)) for all patients were for L2–4: − 0.6 (− 0.9, − 0.3), FN: − 0.8 (− 1.0, − 0.5) and TB: − 0.5 (− 0.8, − 0.2). All scores were significantly different from those of a control population (p < 0.001). For all three variables (ZL2–4, ZFN, ZTB) there were significant differences between the stages. The difference for ZL2–4 was still significant after adjustment for risk factors.

We conclude that BMD is low in COPD patients and decreases with increasing severity of the disease. Low BMD may to some extent be a disease-specific effect.

Introduction

Chronic obstructive pulmonary disease (COPD) appears to be associated with low bone mineral density (BMD) [1], [2], [3], [4], [5] and a higher risk of fractures [4], [6], [7], [8], [9]. In these patients there is a high prevalence of factors known to contribute to BMD loss, like smoking [10], inactivity [11], nutritional impairment [12], corticosteroid use [8], [9], [13] and changes in acid base balance caused by hypercapnia [14] or hypoxia [15]. When correcting for the influence of these factors, there are few data available for determining whether the disease itself has an effect on BMD loss.

In the present cross-sectional study, our aim was to find out whether BMD was lower in a randomly selected group of COPD patients than in a healthy reference population. Secondly, we wished to explore whether the severity of COPD had an impact on BMD, and thirdly, to what extent reduced BMD was associated with the disease itself or with known risk factors for osteoporosis that are often present in patients with COPD.

Section snippets

Subjects

A total of 142 subjects were randomly selected from a population of 363 consecutively admitted COPD patients attending a 4 week rehabilitation program at Glittreklinikken, Norway, in 1998 (weeks 37–50) and 1999 (weeks 18–24 and 34–48). The clinic offers rehabilitation programs for lung patients with various diagnoses and disease severity, who are referred from all over the country.

The diagnosis was based on previous clinical history and on FEV1 < 80% and FEV1/FVC < 70% [16]. Spirometry measurements

Results

The total number of 363 COPD patients admitted to the clinic in the period, consisted of 186 men and 177 women. The randomly selected group of 142 patients consisted of 86 men and 56 women; of these 41 were excluded (Table 1) and 13 declined the invitation. This resulted in a study group of 88 patients, 57 men and 31 women.

Age and FEV1 did not differ between the study group and the total patient group. However, the proportion of men was significantly higher in the study group (Table 2), owing

Discussion

We found that BMD was significantly lower in COPD patients than in a healthy reference population and that it decreased with increasing severity of COPD. Even after adjusting for variables known to be risk factors for osteoporosis, there were significant differences in ZL2–4 for patients in stage IV compared with those in stages II and III, indicating a disease-specific effect of COPD on lumbar BMD. Bolton et al. also found an association between BMD loss and severity of lung disease [23].

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