Table 4.

Associations between vitamin D status and risk of chronic LBP by season of blood sample collection*

	Summer/autumn		Winter/spring
	OR (95% CI)	p	OR (95% CI)	p
Total data set
25(OH)D (nmol/L)		0.87†		0.79†
<50.0	1.00 (Reference)		1.00 (Reference)
50.0–74.9	0.93 (0.72 to 1.20)		1.08 (0.85 to 1.38)
≥75.0	0.96 (0.66 to 1.39)		0.96 (0.58 to 1.58)
Per 10 nmol/L	0.99 (0.93 to 1.06)	0.78	1.03 (0.97 to 1.10)	0.37
Women
25(OH)D (nmol/L)		0.56†		0.27†
<50.0	1.00 (Reference)		1.00 (Reference)
50.0–74.9	1.13 (0.81 to 1.57)		1.26 (0.92 to 1.73)
≥75.0	0.89 (0.53 to 1.47)		1.34 (0.76 to 2.35)
Per 10 nmol/L	1.00 (0.92 to 1.09)	0.94	1.11 (1.02 to 1.20)	0.012
Men
25(OH)D (nmol/L)		0.15†		0.20†
<50.0	1.00 (Reference)		1.00 (Reference)
50.0–74.9	0.70 (0.46 to 1.05)		0.84 (0.56 to 1.27)
≥75.0	1.01 (0.58 to 1.76)		0.37 (0.12 to 1.17)
Per 10 nmol/L	0.97 (0.88 to 1.08)	0.58	0.90 (0.81 to 1.01)	0.08

*Adjustment for age, sex, work status, physical activity at work and in leisure time, education, smoking, body mass index, and subsample.

†For categorical effect.

25(OH)D, 25-hydroxyvitamin D; LBP, low back pain.