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Table 6 Non-genetic factors and risk of anti-CCP-positive and anti-CCP-negative rheumatoid arthritis, Denmark 1998 to 2003

From: Environmental risk factors differ between rheumatoid arthritis with and without auto-antibodies against cyclic citrullinated peptides

 

Anti-CCP-positive rheumatoid arthritis

Anti-CCP-negative rheumatoid arthritis

Test for homogeneity anti-CCP-positive versus anti-CCP-negative rheumatoid arthritis (p)

 

Number of patients/controls

ORa (95% CI)

ORb (95% CI)

Number of patients/controls

ORa (95% CI)

ORb (95% CI)

 

Age at menarche (women only)

       

   ≤12 years

48/145

1 (ref)

1 (ref)

27/145

1 (ref)

1 (ref)

 

   13 years

52/130

1.24 (0.77 to 1.99)

1.33 (0.79 to 2.26)

22/130

0.88 (0.47 to 1.66)

1.06 (0.52 to 2.14)

 

   14 years

46/105

1.35 (0.82 to 2.22)

1.54 (0.88 to 2.69)

26/105

1.24 (0.67 to 2.29)

1.86 (0.93 to 3.70)

0.68

   ≥15 years

52/80

1.91 (1.16 to 3.16)

2.07 (1.18 to 3.63)

27/80

1.75 (0.93 to 3.29)

2.27 (1.13 to 4.57)

 

   Trend test (p)

 

0.01

0.01

 

0.06

0.01

 

Oral contraceptive pills (women only)

       

   Never

64/165

1 (ref)

1 (ref)

33/165

1 (ref)

1 (ref)

 

   Ever

145/312

1.37 (0.93 to 2.02)

1.65 (1.06 to 2.57)

70/312

1.20 (0.73 to 1.98)

1.19 (0.68 to 2.07)

0.34

   Test for homogeneity (p)

 

0.11

0.03

 

0.48

0.53

 

Marital status

       

   Married or cohabiting with partner

227/581

1 (ref)

1 (ref)

106/581

1 (ref)

1 (ref)

 

   Widowed

8/24

0.79 (0.33 to 1.89)

0.50 (0.19 to 1.34)

5/24

0.86 (0.30 to 2.47)

0.72 (0.23 to 2.24)

 

   Divorced or separated

30/99

0.76 (0.48 to 1.19)

0.62 (0.36 to 1.04)

11/99

0.58 (0.29 to 1.13)

0.48 (0.22 to 1.06)

0.77

   Unmarried

44/65

1.98 (1.25 to 3.14)

1.65 (0.96 to 2.84)

14/65

1.47 (0.75 to 2.92)

1.19 (0.53 to 2.67)

 

   Test for homogeneity (p)

 

0.01

0.03

 

0.24

0.28

 

Smoker status

       

   Never

84/298

1 (ref)

1 (ref)

51/298

1 (ref)

1 (ref)

 

   Former

60/155

1.53 (1.02 to 2.29)

1.57 (0.99 to 2.48)

33/155

1.41 (0.84 to 2.34)

1.35 (0.76 to 2.39)

0.03

   Current

165/316

2.13 (1.54 to 2.95)

1.73 (1.17 to 2.56)

52/316

1.01 (0.65 to 1.57)

0.83 (0.49 to 1.39)

 

   Test for homogeneity (p)

 

<0.001

0.02

 

0.35

0.22

 

Pack-years smoked c

       

   0 pack-years

84/298

1 (ref)

1 (ref)

51/298

1 (ref)

1 (ref)

 

   >0 to 10 pack-years

51/142

1.32 (0.86 to 2.01)

1.31 (0.81 to 2.12)

27/142

1.22 (0.71 to 2.08)

1.20 (0.66 to 2.17)

 

   >10 to 20 pack-years

73/125

2.47 (1.65 to 3.69)

2.41 (1.51 to 3.82)

19/125

0.84 (0.46 to 1.52)

0.72 (0.37 to 1.40)

0.08

   >20 pack-years

100/196

2.25 (1.53 to 3.32)

1.65 (1.03 to 2.64)

37/196

1.31 (0.78 to 2.19)

1.00 (0.54 to 1.88)

 

   Trend test (p)

 

<0.001

0.03

 

0.47

0.76

 

Coffee consumption d

       

   0 cups per day

44/142

1 (ref)

1 (ref)

25/142

1 (ref)

1 (ref)

 

   >0 to 5 cups per day

110/326

1.20 (0.76 to 1.91)

1.33 (0.77 to 2.30)

53/326

0.84 (0.47 to 1.53)

0.79 (0.41 to 1.52)

 

   >5 to 10 cups per day

112/234

1.83 (1.12 to 2.97)

1.70 (0.95 to 3.05)

45/234

1.07 (0.57 to 2.00)

0.94 (0.47 to 1.90)

0.46

   >10 cups per day

43/65

2.75 (1.52 to 4.99)

2.18 (1.07 to 4.42)

13/65

1.38 (0.61 to 3.15)

1.23 (0.48 to 3.16)

 

   Trend test (p)

 

<0.001

0.02

 

0.22

0.44

 

Alcohol consumption d,e

       

   0 drinks per week

58/93

1.68 (1.10 to 2.55)

1.98 (1.22 to 3.19)

18/93

0.88 (0.48 to 1.64)

0.72 (0.34 to 1.48)

 

   >0 to 5 drinks per week

124/302

1 (ref)

1 (ref)

60/302

1 (ref)

1 (ref)

 

   >5 to 10 drinks per week

63/163

0.96 (0.66 to 1.39)

1.10 (0.73 to 1.66)

27/163

0.89 (0.53 to 1.48)

1.01 (0.58 to 1.74)

0.01

   >10 to 15 drinks per week

26/75

0.82 (0.49 to 1.38)

0.98 (0.55 to 1.76)

9/75

0.67 (0.31 to 1.45)

0.78 (0.33 to 1.84)

 

   >15 drinks per week

32/130

0.58 (0.35 to 0.94)

0.60 (0.35 to 1.04)

21/130

1.36 (0.73 to 2.52)

1.36 (0.68 to 2.74)

 

   Trend test (p)

 

0.002

0.01

 

0.45

0.34

 

Wine consumption d

       

   0 glasses per week

96/200

1.18 (0.86 to 1.63)

1.18 (0.82 to 1.71)

36/200

0.98 (0.62 to 1.55)

0.86 (0.51 to 1.45)

 

   >0 to 5 glasses per week

168/390

1 (ref)

1 (ref)

72/390

1 (ref)

1 (ref)

 

   >5 to 10 glasses per week

30/124

0.52 (0.33 to 0.81)

0.59 (0.36 to 0.98)

17/124

0.77 (0.43 to 1.38)

0.76 (0.39 to 1.45)

0.03

   >10 to 15 glasses per week

7/33

0.46 (0.20 to 1.09)

0.45 (0.17 to 1.21)

6/33

0.99 (0.38 to 2.56)

0.83 (0.27 to 2.61)

 

   >15 glasses per week

5/19

0.66 (0.24 to 1.84)

0.90 (0.29 to 2.76)

5/19

1.59 (0.54 to 4.66)

2.29 (0.71 to 7.42)

 

   Trend test (p)

 

0.003

0.04

 

0.77

0.46

 

Body mass index d

       

   <18.5 kg/m2 (underweight)

19/41

1.22 (0.65 to 2.29)

0.88 (0.43–1.80)

4/41

0.34 (0.10 to 1.19)

0.35 (0.09 to 1.34)

 

   18.5 to <25 kg/m2 (normal weight)

184/464

1 (ref)

1 (ref)

77/464

1 (ref)

1 (ref)

 

   25 to <30 kg/m2 (overweight)

77/196

1.04 (0.74 to 1.45)

1.01 (0.69 to 1.47)

35/196

1.20 (0.75 to 1.93)

1.24 (0.74 to 2.10)

0.004

   ≥30 kg/m2 (obese)

25/51

1.34 (0.79 to 2.28)

1.15 (0.62 to 2.13)

20/51

3.22 (1.73 to 5.98)

3.45 (1.73 to 6.87)

 

   Trend test (p)

 

0.53

0.63

 

<0.001

<0.001

 

Physical activity at work d

       

   Not physically demanding

34/153

1 (ref)

1 (ref)

23/153

1 (ref)

1 (ref)

 

   Slightly physically demanding

63/177

1.60 (0.99 to 2.58)

1.10 (0.65 to 1.87)

39/177

1.51 (0.85 to 2.69)

1.41 (0.74 to 2.67)

 

   Moderately physically demanding

93/191

2.24 (1.41 to 3.54)

1.64 (0.98 to 2.73)

30/191

1.08 (0.59 to 1.97)

1.02 (0.52 to 1.99)

0.84

   Very physically demanding

70/152

2.03 (1.26 to 3.27)

1.18 (0.68 to 2.06)

34/152

1.53 (0.84 to 2.77)

1.33 (0.66 to 2.67)

 

   Unemployed

48/96

2.58 (1.45 to 4.61)

1.95 (1.00 to 3.81)

10/96

0.47 (0.18 to 1.23)

0.41 (0.13 to 1.23)

 

   Trend test (p)f,g

 

0.002

0.30

 

0.34

0.57

 

Physical activity in leisure time d

       

   Not physically demanding

35/57

1 (ref)

1 (ref)

11/57

1 (ref)

1 (ref)

 

   Slightly physically demanding

108/226

0.74 (0.45 to 1.21)

0.97 (0.56 to 1.70)

49/226

0.95 (0.45 to 1.98)

0.87 (0.39 to 1.94)

 

   Moderately physically demanding

137/405

0.51 (0.32 to 0.83)

0.76 (0.43 to 1.32)

66/405

0.69 (0.33 to 1.42)

0.76 (0.34 to 1.67)

0.75

   Very physically demanding

29/80

0.60 (0.32 to 1.13)

0.90 (0.44 to 1.86)

10/80

0.60 (0.23 to 1.59)

0.59 (0.20 to 1.70)

 

   Trend test (p)f

 

0.008

0.32

 

0.10

0.29

 

Pets as adult

       

   Never

52/87

1 (ref)

1 (ref)

20/87

1 (ref)

1 (ref)

 

   Ever

257/682

0.59 (0.40 to 0.87)

0.62 (0.39 to 0.99)

116/682

0.65 (0.37 to 1.14)

0.61 (0.33 to 1.16)

0.98

   Test for homogeneity (p)

 

0.01

0.04

 

0.13

0.13

 

Asthma h

       

   Never

288/699

1 (ref)

1 (ref)

131/699

1 (ref)

1 (ref)

 

   Ever

21/68

0.73 (0.43 to 1.23)

0.58 (0.32 to 1.08)

4/68

0.32 (0.11 to 0.91)

0.28 (0.09 to 0.85)

0.23

   Test for homogeneity (p)

 

0.23

0.09

 

0.03

0.02

 

Schizophrenia among first-degree relatives

       

   No

299/758

1 (ref)

1 (ref)

134/758

1 (ref)

1 (ref)

 

   Yes

10/11

3.36 (1.32 to 8.51)

4.18 (1.54 to 11.3)

2/11

1.16 (0.24 to 5.55)

0.51 (0.06 to 4.44)

0.16

   Test for homogeneity (p)

 

0.01

0.005

 

0.85

0.54

 
  1. Due to missing values for some individuals, numbers do not always add up to 309 anti-CCP-positive and 136 anti-CCP-negative patients with RA and 769 controls. aAdjusted for gender, birth year, and year or pseudo-year of RA diagnosis. bAdjusted for gender, birth year, year or pseudo-year of RA diagnosis, place of residence, educational status, history of urinary tract infection, and all other variables in the table. Smoking variables not adjusted for the other measure of smoking, and alcohol and wine variables not adjusted for each other. cOne pack-year is equivalent to 7,300 cigarettes (20 cigarettes per day for 1 year). dTen years prior to interview. eOne drink is equivalent to one bottle of normal beer, 0.67 bottle of strong beer, or one glass of wine, dessert wine, or spirits. fTrend tests based on original categories enumerated by consecutive numbers starting with one. gIncluding only individuals who were employed. hPhysician-verified diagnosis before age 45 years. CI, confidence interval; OR, odds ratio; ref, reference.
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Arthritis Research & Therapy

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