Table 2 Associations in HUNT2 between use of systemic MHT and prevalence of chronic LBP in cross-sectional analysis, among nonpregnant women aged 40–69 years

Use of systemic MHT

 Number of women included

12,974

11,072

 Never

9600

2682 (27.9)

1.00 (reference)

1.00 (reference)

 Former

997

425 (42.6)

1.47 (1.36–1.59)

1.46 (1.34–1.59)

 Current

2377

900 (37.9)

1.30 (1.22–1.38)

1.29 (1.20–1.38)

 P for categorical effect

 < 0.001

 < 0.001

Duration of use of systemic MHT (year)

 Number of women included

11,988

10,284

 Never used

9600

2682 (27.9)

1.00 (reference)

1.00 (reference)

 0-2^c

1256

509 (40.5)

1.40 (1.30–1.51)

1.39 (1.28–1.50)

 3–5

682

250 (36.7)

1.25 (1.12–1.39)

1.27 (1.13–1.42)

 6–8

224

86 (38.4)

1.29 (1.09–1.53)

1.31 (1.10–1.56)

 ≥ 9

226

112 (49.6)

1.68 (1.47–1.93)

1.63 (1.40–1.89)

 P for categorical effect

 < 0.001

 < 0.001

 P for linear trend^d

0.25

0.41

Use of systemic MHT by type in current users

 Number of women included

11,825

10,107

 Never used systemic

9600

2682 (27.9)

1.00 (reference)

1.00 (reference)

 Oestrogen only

554

238 (43.0)

1.46 (1.32–1.62)

1.45 (1.30–1.62)

 Combination

1671

604 (36.1)

1.24 (1.15–1.34)

1.23 (1.14–1.34)

 P for categorical effect

 < 0.001

 < 0.001

 P for difference between oestrogen only and combination

0.051

0.042