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

Table 3 Associations between use of systemic MHT in HUNT2 and risk of chronic LBP in HUNT3 in cohort analysis, among nonpregnant women aged 40–69 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 systemic MHT
Number of women included			6007	5330
Never	4559	904 (19.8)	1.00 (reference)	1.00 (reference)
Former	385	79 (20.5)	1.06 (0.86–1.31)	1.03 (0.83–1.29)
Current	1063	262 (24.6)	1.30 (1.14–1.47)	1.30 (1.14–1.49)
P for categorical effect			< 0.001	0.001
Duration of use of systemic MHT (year)
Number of women included			5564	4955
Never used	4559	904 (19.8)	1.00 (reference)	1.00 (reference)
0-2^c	513	106 (20.7)	1.08 (0.90–1.29)	1.13 (0.94–1.36)
3–5	321	82 (25.5)	1.36 (1.11–1.66)	1.39 (1.12–1.72)
6–8	96	26 (27.1)	1.48 (1.06–2.08)	1.45 (1.02–2.07)
≥ 9	75	26 (34.7)	1.83 (1.33–2.51)	1.84 (1.31–2.59)
P for categorical effect			< 0.001	0.001
P for linear trend^d			0.001	0.003
Use of systemic MHT by type in current users
Number of women included			5554	4933
Never used systemic	4559	904 (19.8)	1.00 (reference)	1.00 (reference)
Oestrogen only	216	56 (25.9)	1.37 (1.08 -1.74)	1.49 (1.16–1.91)
Combination	779	195 (25.0)	1.33 (1.16–1-54)	1.35 (1.16–1.57)
P for categorical effect			< 0.001	< 0.001
P for difference between oestrogen only and combination			0.54	0.18

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

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