Table 4.

Iron and colorectal adenoma risk in the serologic sample (n = 356 cases; n = 396 controls) from the PLCO Cancer Screening Trial

VariableQ1Q2Q3Q4Ptrend
Dietary variables
Red meat (g/1,000 kcal)
 Quartile median, quartile cutoff points13.8 (≤20.1)26.2 (>20.1–31.3)37.5 (>31.3–46.8)59.8 (>46.8)
 Cases/controls72/9670/9696/96104/96
 ORa (95% CI)Ref0.97 (0.63–1.50)1.33 (0.88–2.02)1.45 (0.96–2.20)0.04
 ORb (95% CI)Ref1.08 (0.69–1.71)1.42 (0.91–2.21)1.59 (1.02–2.49)0.03
Total dietary iron, mg/1,000 kcal
 Quartile median (quartile cutoff points)6.6 (≤7.4)8.1 (>7.4–8.7)9.4 (>8.7–10.3)11.6 (>10.3)
 Cases/controls74/96108/9687/9673/96
 ORa (95% CI)Ref1.46 (0.97–2.20)1.18 (0.77–1.79)0.99 (0.64–1.52)0.54
 ORb (95% CI)Ref1.49 (0.97–2.28)1.24 (0.80–1.92)0.98 (0.62–1.55)0.98
Heme iron, mg/1,000 kcal
 Quartile median (quartile cutoff points)76.3 (≤108.0)141.4 (>108.0–170.1)211.0 (>170.1–259.5)355.7 (>259.5)
 Cases/controls74/9577/9683/96105/96
 ORa (95% CI)Ref1.03 (0.67–1.58)1.11 (0.72–1.69)1.41 (0.93–2.14)0.07
 ORb (95% CI)Ref1.08 (0.69–1.69)1.09 (0.69–1.71)1.46 (0.94–2.29)0.08
Serologic indices
Ferritin (ng/mL)
 Quartile median (quartile cutoff points)54 (≤83)119 (>83–161)209 (>161–276)419 (>276)
 Cases/controls80/98125/10077/9974/99
 ORa (95% CI)Ref1.53 (1.03–2.29)0.96 (0.63–1.46)0.92 (0.60–1.41)0.15
 ORb (95% CI)Ref1.60 (1.05–2.43)0.93 (0.59–1.47)0.86 (0.53–1.38)0.08
Iron, μg/dL
 Quartile median (quartile cutoff points)74 (≤86)96 (>86–105)118 (>105–130)154 (>130)
 Cases/controls95/10177/9588/10096/100
 ORa (95% CI)Ref0.86 (0.57–1.30)0.94 (0.63–1.40)1.02 (0.69–1.52)0.77
 ORb (95% CI)Ref0.85 (0.55–1.30)0.95 (0.63–1.45)1.02 (0.66–1.55)0.78
Transferrin saturation, %
 Quartile median (quartile cutoff points)20 (≤24)27 (>24–29)33 (>29–37)43 (>37)
 Cases/controls82/9873/95102/10799/96
 ORa (95% CI)Ref0.92 (0.60–1.40)1.14 (0.76–1.70)1.23 (0.82–1.85)0.20
 ORb (95% CI)Ref0.92 (0.59–1.43)1.18 (0.78–1.79)1.28 (0.83–1.98)0.16
TIBC, μg/dL
 Quartile median (quartile cutoff points)300 (≤323)338 (>323–351)369 (>351–389)421 (>389)
 Cases/controls119/9772/10282/9783/100
 ORa (95% CI)Ref0.58 (0.38–0.86)0.69 (0.46–1.03)0.68 (0.45–1.01)0.10
 ORb (95% CI)Ref0.51 (0.34–0.78)0.62 (0.41–0.95)0.57 (0.37–0.88)0.03
UIBC, μg/dL
 Quartile median (quartile cutoff points)185 (≤209)228 (>209–243)263 (>243–280)314 (>280)
 Cases/controls118/9877/10180/9981/98
 ORa (95% CI)Ref0.63 (0.42–0.95)0.67 (0.45–1.00)0.69 (0.46–1.02)0.08
 ORb (95% CI)Ref0.59 (0.39–0.90)0.60 (0.39–0.91)0.62 (0.40–0.95)0.04
  • aOR adjusted for age only.

  • bMultivariate OR adjusted for age (≤59, 60–64, 65–69, ≥70 years), gender, season of blood draw (May–Sep, Oct–Apr), sigmoidoscopy interval (3 or 5 years), race (non-Hispanic white, other), study center, year of entry to study, education (≤12 years or completed high school, post–high school training other than college/some college, college graduate or postgraduate), smoking (never, former, current, cigar/pipe), regular NSAID use (yes/no), and family history of colorectal cancer (yes/no).