Menopausal hormone therapy, oral contraceptives and risk of chronic low back pain: the HUNT Study

Table 5 Associations between use of OC in HUNT2 and risk of chronic LBP in HUNT3 in cohort analysis, among women aged 20–69 years at baseline

	Total number of women^a	Number of women with chronic LBP (%)^a	RR (95% CI) with adjustment for age only	RR (95% CI) with comprehensive adjustment^b
Use of OC
Number of women included			10,586	9113
Never	4523	869 (19.2)	1.00 (reference)	1.00 (reference)
Former	5066	1049 (20.7)	1.15 (1.05–1.27)	1.17 (1.06–1.30)
Current	997	166 (16.6)	1.03 (0.86–1.23)	1.07 (0.88–1.29)
P for categorical effect			0.010	0.008
Duration of use of OC (year)
Number of women included			10,322	8899
0	4523	869 (19.2)	1.00 (reference)	1.00 (reference)
0-4^c	2833	571 (20.2)	1.16 (1.04–1.30)	1.18 (1.05–1.33)
5–9	1794	357 (19.9)	1.18 (1.04–1.35)	1.22 (1.06–1.40)
10–14	833	172 (20.6)	1.17 (1.00–1.38)	1.20 (1.02–1.41)
≥ 15	339	63 (18.6)	1.02 (0.80–1.29)	1.02 (0.80–1.30)
P for categorical effect			0.039	0.021
P for linear trend^d			0.56	0.54

OC Oral contraceptives, HUNT Trøndelag Health Study, LBP Low back pain, RR Relative risk, CI Confidence interval, MHT Menopausal hormone therapy
^aIn analysis adjusted for age only
^bAdjustment for age, BMI, physical activity, education, smoking, age at menarche, nulliparity, age at first childbirth, use of systemic MHT
^cMust have used OC for at least one month
^dAmong all women who had used OC for at least one month

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