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Table 1 Age-standardized characteristics of the subjects in the Nurses' Health Study in 1990

From: Protein, iron, and meat consumption and risk for rheumatoid arthritis: a prospective cohort study

  Total protein (g/day) Heme iron (g/day)
Quintile 1 3 5 1 3 5
Intake (mean) 60.1 74.1 90.7 0.77 1.20 1.81
Number of women 15,836 15,822 15,824 15,843 15,996 15,649
Age (mean; years)) 56.4 56.3 57.1 57.3 56.4 56.3
Body mass index (mean; kg/m2) 24.7 25.5 27.1 24.6 25.8 26.6
Current smoker (%) 23 16 14 14 17 21
Age at menarche (mean; years) 12.6 12.5 12.3 12.5 12.5 12.4
Breastfeeding ≥12 months among parous women (%) 14 17 17 18 17 13
Very regular menses (%)a 53 56 54 56 57 50
Mean nutrient intakes       
   Protein (g/day) - - - 67.1 74.6 82.5
   Animal protein (g/day) 42.4 55.8 73.0 47.3 56.5 66.7
   Vegetable protein (g/day) 17.7 18.2 17.7 19.8 18.1 15.7
   Heme iron (g/day) 0.98 1.25 1.50 - - -
   Total iron (g/day) 14.0 15.5 16.5 15.8 15.6 14.8
  1. A total of 79,173 are included, and findings are presented according to lowest, middle, and highest consumption categories of total protein and total heme iron. Values are presented as mean or percentage of the population within each category, and are standardized to the age distribution of the study population over follow up from 1980 to 1990. The lowest, middle, and highest categories are three of the five consumption categories used in Tables 2 to 4. aAt age 20 to 35 years.