Table 2

Rate ratios of rheumatoid arthritis by protein and iron intakes among women in the Nurses' Health Study, 1980 to 2002
Nutrients
 Quintile
 Median intake
 Number of cases
 Age-adjusteda rate ratio (95% CI)
 Multivariateb rate ratio (95% CI)
Total proteinc
 1
 60.8 g/day
 95
 1.00
 1.00

2
 68.4 g/day
 109
 1.12 (0.86–1.48)
 1.11 (0.84, 1.47)

3
 73.9 g/day
 89
 0.90 (0.67–1.20)
 0.90 (0.67, 1.21)

4
 79.5 g/day
 133
 1.35 (1.04–1.76)
 1.34 (1.03, 1.76)

5
 89.0 g/day
 120
 1.23 (0.94–1,61)
 1.17 (0.88, 1.55)




P for trend = 0.04d
 P for trend = 0.12d
Animal proteine
 1
 42.5 g/day
 101
 1.00
 1.00

2
 50.4 g/day
 99
 0.97 (0.74–1.28)
 0.93 (0.71–1.24)

3
 56.1 g/day
 104
 1.02 (0.78–1.34)
 1.03 (0.78–1.36)

4
 62.3 g/day
 125
 1.23 (0.95–1.60)
 1.21 (0.92–1.59)

5
 72.9 g/day
 117
 1.13 (0.87–1.49)
 1.13 (0.84–1.50)




P for trend = 0.08d
 P for trend = 0.14d
Vegetable proteine
 1
 12.2 g/day
 111
 1.00
 1.00

2
 15.5 g/day
 95
 0.81 (0.61–1.06)
 0.83 (0.62–1.11)

3
 17.5 g/day
 101
 0.82 (0.62–1.08)
 0.89 (0.66–1.21)

4
 19.3 g/day
 127
 1.04 (0.79–1.36)
 1.14 (0.84–1.55)

5
 22.2 g/day
 112
 0.90 (0.67–1.20)
 1.02 (0.74–1.41)




P for trend = 0.89d
 P for trend = 0.36d
Total iron intake (diet and supplements)f
 1
 8.00 mg/day
 101
 1.00
 1.00

2
 10.0 mg/day
 110
 1.01 (0.76–1.34)
 1.01 (0.76–1.35)

3
 11.8 mg/day
 111
 1.00 (0.75–1.33)
 0.99 (0.74–1.33)

4
 15.2 mg/day
 117
 1.12 (0.84–1.49)
 1.10 (0.81–1.48)

5
 24.4 mg/day
 107
 1.00 (0.75–1.34)
 1.00 (0.74–1.36)




P for trend = 0.81d
 P for trend = 0.98d
Dietary irong
 1
 8.10 mg/day
 117
 1.00
 1.00

2
 9.78 mg/day
 80
 0.90 (0.67–1.20)
 1.01 (0.76–1.35)

3
 10.6 mg/day
 113
 1.01 (0.77–1.34)
 0.99 (0.74–1.33)

4
 11.9 mg/day
 114
 1.10 (0.83–1.44)
 1.10 (0.81–1.48)

5
 14.4 mg/day
 122
 1.20 (0.92–1.56)
 1.00 (0.74–1.36)




P for trend = 0.21d
 P for trend = 0.92d
Iron from supplementsg
 1
 0.00 mg/day
 371
 1.00
 1.00

2
 2.08 mg/day
 41
 0.73 (0.52–1.03)
 0.79 (0.56–1.11)

3
 10.0 mg/day
 134
 0.92 (0.75–1.12)
 0.94 (0.77–1.16)




P for trend = 0.27d
 P for trend = 0.68d

1
 0.80 mg/day
 99
 1.00
 1.00
Heme iron intakeh
 2
 1.04 mg/day
 121
 1.21 (0.92–1.57)
 1.16 (0.88–1.52)

3
 1.23 mg/day
 106
 1.08 (0.82–1.42)
 0.99 (0.74–1.31)

4
 1.46 mg/day
 113
 1.08 (0.82–1.43)
 0.99 (0.74–1.32)

5
 1.90 mg/day
 107
 1.18 (0.89–1.57)
 0.96 (0.70–1.31)




P for trend = 0.49d
 P for trend = 0.51d

In all, 82,063 women were included and there were 546 incident cases of rheumatoid arthritis (RA). Diet was assessed in 1980, 1984, 1986, 1990, 1994, and 1998. Nutrient intakes were cumulatively updated over follow up. Total intakes include multivitamins and supplements. Dietary intakes are from food sources only. aThe age-adjusted models were adjusted for the total energy intake as well as age. bThe multivariate models were adjusted for age, body mass index, smoking, and total lifetime breastfeeding. cProtein was adjusted for total iron as well as for the same variables adjusted for in all the multivariate models. dAll P values for trend were calculated with median intake of each nutrient in each quintile as a continuous variable. eAnimal and vegetable protein were adjusted for each other, total iron, and for the same variables adjusted for in all the multivariate models. fTotal iron was adjusted for total protein as well as for the same variables adjusted for in all the multivariate models. gDietary and supplemental iron were adjusted for each other, total protein, and the same variables adjusted for in all of the multivariate models; supplemental iron is given in tertiles. hHeme iron models are additionally adjusted for total protein. CI, confidence interval.

Benito-Garcia et al. Arthritis Research & Therapy 2007 9:R16   doi:10.1186/ar2123

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