Vitamin D status is associated with bone mineral density and functional exercise capacity in patients with chronic obstructive pulmonary disease

Figures & data

Table I. Patients’ characteristics.

	Total group (n = 151)	Normal vitamin D (n = 64)	Vitamin D deficiency (n = 87)	P value
25(OH)D, nmol/L	49.0 ± 16.1	64.4 ± 10.7	37.7 ± 7.9	< 0.001
Men, n (%)	88 (58)	39 (61)	48 (55)	0.479
Age, years	64.8 ± 8.8	64.2 ± 9.1	65.3 ± 8.6	0.479
BMI, kg/m2	25.1 ± 5.4	24.5 ± 3.6	25.6 ± 6.4	0.179
FEV1, % predicted	45.8 ± 16.6	49.2 ± 15.7	43.3 ± 16.8	0.032
FVC, % predicted	94.7 ± 20.6	100.5 ± 20.9	90.5 ± 19.4	0.003
GOLD stage				0.001
II, %	28	38	21
III, %	36	42	31
IV, %	36	20	48
DLCO, % predicted	53.2 ± 19.7	55.6 ± 22.0	51.4 ± 17.7	0.157
PaO2, kPa	9.6 ± 1.3	9.7 ± 1.4	9.6 ± 1.2	0.415
PaCO2, kPa	5.3 ± 0.6	5.2 ± 0.6	5.4 ± 0.6	0.099
MRC score	3.5 ± 1.1	3.6 ± 1.0	3.5 ± 1.1	0.789
BMD
Lumbar spine, g/cm2	1.08 ± 0.20	1.11 ± 0.21	1.06 ± 0.19	0.088
Hip, g/cm2	0.82 ± 0.14	0.84 ± 0.15	0.80 ± 0.14	0.073
Total, g/cm2	1.08 ± 0.12	1.10 ± 0.11	1.07 ± 0.12	0.168
Lowest T score	–1.98 ± 1.12	–1.78 ± 1.12	–2.13 ± 1.11	0.059
Bone classification
Normal bone, %	21	26	16
Osteopenia, %	41	44	39
Osteoporosis, %	38	30	45
Muscle mass and strength
FFMI, kg/m2	17.2 ± 2.3	17.2 ± 2.2	17.2 ± 2.3	0.947
QMVC, kg	28.6 ± 9.8	29.9 ± 9.6	27.4 ± 9.9	0.207
QMVC/FFM	0.59 ± 0.16	0.62 ± 0.15	0.57 ± 0.17	0.159
6MWD, m	425.7 ± 122.0	477.7 ± 124.2	387.0 ± 105.3	< 0.001
Vitamin D intake, μg	5.5 ± 3.1	5.6 ± 3.4	5.5 ± 2.9	0.843
Use of corticosteroids (%)
Oral	13.9	6.3	19.5	0.059
Inhaled	88.1	87.5	88.5	0.897

Results are presented as mean ± standard deviation unless otherwise indicated. The P values represent the differences between normal vitamin D and vitamin D deficiency.

25(OH)D = 25-hydroxyvitamin D; 6MWD = 6-minute walking distance; BMD = bone mineral density; BMI = body mass index; D_LCO = diffusing capacity for carbon monoxide; FEV₁ = forced expiratory volume in the first second; FFM = fat-free mass; FFMI = fat-free mass index; FVC = forced vital capacity; MRC = Medical Research Council dyspnoea scale; PaCO₂ = partial pressure of carbon dioxide in arterial blood; PaO₂ = partial pressure of oxygen in arterial blood; QMVC = quadriceps maximum voluntary contraction strength.

Figure 1. Plasma 25(OH)D concentrations among the GOLD stages.

Table II. Univariate regression analyses for bone mineral density (T score).

	B	95% CI	P-value
Men	0.188	–0.177 to 0.553	0.311
Age	–0.022	–0.042 to –0.002	0.035
BMI	0.077	0.046 to 0.109	< 0.001
FEV1	0.011	0.000 to 0.022	0.044
25(OH)D	0.012	0.001 to 0.023	0.034
6MWD	0.001	0.000 to 0.003	0.109
Oral corticosteroids	0.032	0.000 to 0.000	0.697
Inhaled corticosteroids	0.032	0.000 to 0.000	0.696

25(OH)D = 25-hydroxyvitamin D; 6MWD = 6-minute walking distance; BMI = body mass index; FEV₁ = forced expiratory volume in 1 second.

Table III. Multivariate regression analyses for bone mineral density (T score).

	B	95% CI	P value
Age	–0.024	–0.042 to –0.005	0.011
BMI	0.078	0.047 to 0.109	< 0.001
FEV1	0.005	–0.005 to 0.015	0.360
25(OH)D	0.015	0.005 to 0.025	0.005

Adjusted R² = 0.22.

25(OH)D = 25-hydroxyvitamin D; BMI = body mass index; FEV₁ = forced expiratory volume in 1 second.

Table IV. Univariate regression analyses for quadriceps muscle strength and 6MWD.

	QMVC			6MWD
	B	95% CI	P value	B	95% CI	P value
Men	11.529	8.357 to 14.701	< 0.001	36.463	–3.023 to 75.949	0.070
Age	–0.215	–0.433 to 0.003	0.053	–4.162	–6.292 to –2.033	< 0.001
Height	0.591	0.421 to 0.761	< 0.001	3.103	0.939 to 5.267	0.005
FFMI	2.541	1.782 to 3.299	< 0.001	3.774	–5.083 to 12.631	0.401
FEV1	0.158	0.045 to 0.271	0.007	1.443	0.273 to 2.613	0.016
25(OH)D	0.097	–0.019 to 0.212	0.099	2.778	1.635 to 3.921	< 0.001
QMVC	–	–	–	5.783	3.696 to 7.871	< 0.001
6MWD	0.041	0.026 to 0.056	< 0.001	–	–	–
MRC	0.792	–1.287 to 2.871	0.450	4.550	–16.754 to 25.853	0.673
Oral corticosteroids	–0.099	–0.002 to 0.001	0.329	–0.009	–0.015 to 0.013	0.908
Inhaled corticosteroids	–0.099	–0.002 to 0.001	0.330	–0.009	–0.015 to 0.013	0.909

25(OH)D = 25-hydroxyvitamin D; 6MWD = 6-minute walking distance; FEV₁ = forced expiratory volume in 1 second; FFMI = fat-free mass index; MRC = Medical Research Council dyspnoea scale; QMVC = quadriceps maximum voluntary contraction strength.

Table V. Multivariate regression analyses for quadriceps muscle strength and 6MWD.

	QMVC			6MWD
	B	95% CI	P value	B	95% CI	P value
Men	4.106	–0.569 to 8.781	0.084	27.941	–34.708 to 90.589	0.378
Age	–0.249	–0.412 to –0.087	0.003	–2.033	–4.404 to 0.338	0.092
Height	0.215	0.009 to 0.421	0.041	–1.368	–4.357 to 1.621	0.366
FFMI	1.403	0.573 to 2.234	0.001	–	–	–
FEV1	0.020	–0.068 to 0.108	0.654	0.491	–0.702 to 1.685	0.416
25(OH)D	0.004	–0.088 to 0.097	0.927	2.489	1.287 to 3.691	< 0.001
QMVC	–	–	–	4.503	1.806 to 7.201	0.001
6MWD	0.023	0.010 to 0.037	0.001	–	–	–

Adjusted R² for QMVC = 0.58. Adjusted R² for 6MWD = 0.37.

25(OH)D = 25-hydroxyvitamin D; 6MWD = 6-minute walking distance; FEV₁ = forced expiratory volume in 1 second; FFMI = fat free mass index; MRC = Medical Research Council dyspnoea scale; QMVC = quadriceps maximum voluntary contraction strength.