Table 4.

Multivariate ORs^* for colorectal adenoma risk associated with intake of total iron (mg/day), dietary iron (mg/1000 kcal), iron from meat (mg/1000 kcal), heme iron from meat (mg/1000 kcal), and supplemental iron (mg/day).

Characteristic	Quartile 1	Quartile 2	Quartile 3	Quartile 4	P Trenda	Continuous (per 10 unit)
Total iron b
Median (Cut-points)	10.8 (≤ 12.6)	15.0 (>12.6–22.9)	28.3 (>22.9–30.2)	33.4 (>56.6)
Cases/Controls	47/161	43/158	29/158	36/159
OR (95% CI)c	1.00	1.21 (0.66–1.92)	0.73 (0.42–1.27)	0.91 (0.52–1.59)	0.34	0.96 (0.79–1.17)
Dietary iron
Median (Cut-points)	6.3 (≤ 7.0)	7.5 (>7.0–8.1)	8.8 (>8.1–9.7)	10.9 (>9.7)
Cases/Controls	36/159	43/161	41/157	35/159
OR (95% CI)	1.00	1.30 (0.76–2.22)	1.55 (0.87–2.75)	1.11 (0.57–2.16)	0.77	1.29 (0.50–3.34)
Iron from meat d
Median (Cut-points)	0.16 (≤ 0.23)	0.31 (>0.23–0.38)	0.47 (>0.38–0.58)	0.78 (>0.58)
Cases/Controls	26/163	47/162	41/162	44/162
OR (95% CI)	1.00	1.67 (0.94–2.96)	1.75 (0.97–3.15)	1.71 (0.94–3.14)	0.17	1.06 (0.87–1.28)e
Heme iron from meat
Median (Cut-points)	0.05 (≤ 0.09)	0.11 (>0.09–0.14)	0.17 (>0.14–0.21)	0.28 (>0.21)
Cases/Controls	30/160	46/162	39/158	40/156
OR (95% CI)	1.00	1.53 (0.88–2.66)	1.50 (0.84–2.66)	1.50 (0.83–2.73)	0.32	1.06 (0.89–1.27)f
Supplemental iron g
Cut-points	0.0	0.3–12.9	18.0–39.4
Cases/Controls	76/247	22/130	57/259
OR (95% CI)	1.00	0.72 (0.41–1.26)	0.82 (0.54–1.25)		0.34	0.94 (0.76–1.15)

^*OR adjusted for age (continuous), education (high school or less, vocational/technical/business, 1–3 years or college/junior college, college graduate, graduate/professional degree), race (White, African-American, other), smoking status (never, former, current), physical activity (no moderate or vigorous activity, moderate, vigorous), BMI (continuous, kg/m²), study center (Bethesda, Portsmouth, San Diego, Washington D.C.), current HRT use (yes, no), family history of colorectal polyps or cancer (yes, no), regular NSAID use (defined as once a week for at least one month at any time prior to three months before colonoscopy; yes, no, don’t know/missing), alcohol intake (<5 g/day, 5–14.9 g/day, ≥15 g/day), fiber (continuous, g/1,000 kcal), dietary calcium (continuous, g/1,000 kcal), calcium from supplements (continuous, g/day), and total caloric intake (continuous, kcal/day).

^aP trend calculated using the median of each quartile.

^bDietary iron (residual energy adjusted) plus iron from supplements.

^cNutrients in this model were residual energy adjusted.

^dLimited to only those meats in the heme iron database.

^ePer 0.30 mg/1000 kcal.

^fPer 0.10 mg/1000 kcal.

^gDue to the small number of people taking supplements containing iron, iron from supplements was broken into three levels.