Table 2 Subgroup analyses for the associations of dietary, total, and heme iron intake with breast cancer risk
From: Iron intake, body iron status, and risk of breast cancer: a systematic review and meta-analysis
Subgroups | Dietary iron intake (highest vs. lowest) | Total iron intake (highest vs. lowest) | Heme iron intake (highest vs. lowest) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
No. of RRs | RR (95% CI) | I2 (%)a | P heterogeneity b | P difference c | No. of RRs | RR (95% CI) | I2 (%)a | P heterogeneity b | No. of RRs | RR (95% CI) | I2 (%)a | P heterogeneity b | |
Overall | 11 | 1.01 (0.89–1.15) | 55 | 0.01 |  | 4 | 0.97 (0.82–1.14) | 46 | 0.14 | 6 | 1.12 (1.04–1.22) | 39 | 0.15 |
Study design | Â | Â | Â | Â | 0.20 | Â | Â | Â | Â | Â | Â | Â | Â |
 Cohort | 4 | 1.10 (0.94–1.27) | 63 | 0.05 |  | 2 | 0.95 (0.75–1.20) | 78 | 0.03 | 5 | 1.10 (1.04–1.16) | 0 | 0.86 |
 Case-control | 7 | 0.91 (0.73–1.12) | 45 | 0.10 |  | 2 | 1.08 (0.79–1.47) | 0 | 0.76 | 1 | 1.50 (1.19–1.88) | NA | NA |
Geographic location | Â | Â | Â | Â | 0.65 | Â | Â | Â | Â | Â | Â | Â | Â |
 North America | 4 | 1.02 (0.90–1.16) | 54 | 0.09 |  | 4 | 0.97 (0.82–1.14) | 46 | 0.14 | 4 | 1.10 (1.04–1.16) | 0 | 0.78 |
 Europe | 5 | 0.93 (0.65–1.34) | 63 | 0.03 |  | 0 | NA | NA | NA | 1 | 1.00 (0.70–1.43) | NA | NA |
 Asia | 2 | 1.23 (0.93–1.62) | 0 | 0.37 |  | 0 | NA | NA | NA | 1 | 1.50 (1.19–1.88) | NA | NA |
Menopausal statusd | Â | Â | Â | Â | 0.78 | Â | Â | Â | Â | Â | Â | Â | Â |
 Premenopausal | 3 | 1.12 (0.94–1.32) | 0 | 0.62 |  | 1 | 0.88 (0.74–1.04) | NA | NA | 3 | 1.21 (0.97–1.51) | 68 | 0.05 |
 Postmenopausal | 5 | 1.11 (0.92–1.33) | 64 | 0.03 |  | 3 | 0.97 (0.81–1.17) | 50 | 0.14 | 5 | 1.08 (0.99–1.18) | 21 | 0.28 |
Study quality | Â | Â | Â | Â | 0.03 | Â | Â | Â | Â | Â | Â | Â | Â |
 High (NOS score ≥ 7) | 5 | 1.12 (0.98–1.29) | 60 | 0.04 |  | 3 | 0.97 (0.81–1.16) | 62 | 0.07 | 6 | 1.12 (1.04–1.22) | 39 | 0.15 |
 Low (NOS score < 7) | 6 | 0.84 (0.72–0.96) | 0 | 0.53 |  | 1 | 1.27 (0.41–3.92) | NA | NA | 0 | NA | NA | NA |
Dietary assessment method | Â | Â | Â | Â | 0.34 | Â | Â | Â | Â | Â | Â | Â | Â |
 Structured interview | 5 | 1.13 (0.85–1.51) | 63 | 0.03 |  | 0 | NA | NA | NA | 2 | 1.25 (0.85–1.86) | 72 | 0.06 |
 Self-administered | 6 | 0.98 (0.84–1.13) | 57 | 0.04 |  | 4 | 0.97 (0.82–1.14) | 46 | 0.14 | 4 | 1.10 (1.04–1.16) | 0 | 0.78 |
Adjustments for confounders | |||||||||||||
 BMI |  |  |  |  | 0.33 |  |  |  |  |  |  |  |  |
  Yes | 9 | 1.05 (0.91–1.21) | 56 | 0.02 |  | 2 | 0.95 (0.75–1.20) | 78 | 0.03 | 6 | 1.12 (1.04–1.22) | 39 | 0.15 |
  No | 2 | 0.86 (0.72–1.02) | 0 | 0.70 |  | 2 | 1.08 (0.79–1.47) | 0 | 0.76 | 0 | NA | NA | NA |
 Physical activity |  |  |  |  | 0.13 |  |  |  |  |  |  |  |  |
  Yes | 3 | 1.22 (0.93–1.59) | 63 | 0.07 |  | 0 | NA | NA | NA | 3 | 1.20 (0.96–1.48) | 70 | 0.04 |
  No | 8 | 0.94 (0.80–1.10) | 52 | 0.04 |  | 4 | 0.97 (0.82–1.14) | 46 | 0.14 | 3 | 1.08 (1.00–1.18) | 0 | 0.64 |
 Alcohol intake |  |  |  |  | 0.95 |  |  |  |  |  |  |  |  |
  Yes | 8 | 1.01 (0.88–1.17) | 61 | 0.01 |  | 2 | 0.95 (0.75–1.20) | 78 | 0.03 | 5 | 1.10 (1.04–1.16) | 0 | 0.86 |
  No | 3 | 1.02 (0.72–1.44) | 55 | 0.11 |  | 2 | 1.08 (0.79–1.47) | 0 | 0.76 | 1 | 1.50 (1.19–1.88) | NA | NA |
 OC and/or HRT use |  |  |  |  | 0.35 |  |  |  |  |  |  |  |  |
  Yes | 5 | 1.08 (0.93–1.25) | 59 | 0.05 |  | 2 | 0.95 (0.75–1.20) | 78 | 0.03 | 5 | 1.10 (1.04–1.16) | 0 | 0.86 |
  No | 6 | 0.93 (0.74–1.17) | 50 | 0.08 |  | 2 | 1.08 (0.79–1.47) | 0 | 0.76 | 1 | 1.50 (1.19–1.88) | NA | NA |
 Family history of breast cancer |  |  |  |  | 0.20 |  |  |  |  |  |  |  |  |
  Yes | 7 | 1.07 (0.93–1.23) | 57 | 0.03 |  | 2 | 0.95 (0.75–1.20) | 78 | 0.03 | 6 | 1.12 (1.04–1.22) | 39 | 0.15 |
  No | 4 | 0.86 (0.69–1.07) | 15 | 0.32 |  | 2 | 1.08 (0.79–1.47) | 0 | 0.76 | 0 | NA | NA | NA |