Table 3 Subgroup analyses for the associations of serum/plasma ferritin and iron with breast cancer risk
From: Iron intake, body iron status, and risk of breast cancer: a systematic review and meta-analysis
Subgroups | Serum/plasma ferritin (highest vs. lowest) | Serum/plasma iron (highest vs. lowest) | ||||||
|---|---|---|---|---|---|---|---|---|
No. of RRs | RR (95% CI) | I2 (%)a | P heterogeneity b | No. of RRs | RR (95% CI) | I2 (%)a | P heterogeneity b | |
Overall | 6 | 1.13 (0.78–1.62) | 65 | 0.01 | 5 | 1.22 (1.01–1.47) | 61 | 0.04 |
Study design | ||||||||
 Cohort | 1 | 0.97 (0.54–1.74) | NA | NA | 4 | 1.27 (1.02–1.59) | 68 | 0.03 |
 Nested case-control/case-cohort | 5 | 1.18 (0.76–1.84) | 72 | 0.01 | 1 | 1.04 (0.78–1.40) | NA | NA |
Geographic location | ||||||||
 North America | 1 | 1.05 (0.77–1.45) | NA | NA | 0 | NA | NA | NA |
 Europe | 1 | 0.67 (0.49–0.92) | NA | NA | 3 | 1.10 (0.95–1.28) | 35 | 0.21 |
 Asia | 3 | 1.81 (1.16–2.83) | 0 | 0.50 | 1 | 1.62 (1.22–2.14) | NA | NA |
 Australia | 1 | 0.97 (0.54–1.74) | NA | NA | 1 | 1.64 (0.90–2.98) | NA | NA |
Menopausal statusc | ||||||||
 Premenopausal | 3 | 0.79 (0.46–1.35) | 61 | 0.08 | 2 | 1.01 (0.84–1.20) | 0 | 0.78 |
 Postmenopausal | 5 | 1.23 (0.87–1.75) | 18 | 0.30 | 2 | 1.39 (0.90–2.15) | 35 | 0.21 |
Study quality | ||||||||
 High (NOS score ≥ 7) | 5 | 1.02 (0.70–1.48) | 61 | 0.04 | 5 | 1.22 (1.01–1.47) | 61 | 0.04 |
 Low (NOS score < 7) | 1 | 1.77 (0.96–3.27) | NA | NA | 0 | NA | NA | NA |
Biological sample | ||||||||
 Serum | 4 | 1.06 (0.61–1.85) | 67 | 0.03 | 5 | 1.22 (1.01–1.47) | 61 | 0.04 |
 Plasma | 2 | 1.27 (0.78–2.09) | 55 | 0.14 | 0 | NA | NA | NA |
Adjustments for confounders | ||||||||
 BMI | ||||||||
  Yes | 3 | 0.86 (0.63–1.19) | 51 | 0.13 | 3 | 1.36 (0.98–1.90) | 61 | 0.08 |
  No | 3 | 1.81 (1.16–2.83) | 0 | 0.50 | 2 | 1.12 (0.91–1.38) | 65 | 0.09 |
 Physical activity | ||||||||
  Yes | 1 | 0.67 (0.49–0.92) | NA | NA | 2 | 1.30 (0.84–2.00) | 78 | 0.03 |
  No | 5 | 1.28 (0.93–1.76) | 31 | 0.21 | 3 | 1.16 (0.94–1.43) | 54 | 0.12 |
 Alcohol intake | ||||||||
  Yes | 2 | 0.74 (0.54–1.03) | 18 | 0.27 | 3 | 1.36 (0.98–1.90) | 61 | 0.08 |
  No | 4 | 1.41 (0.93–2.13) | 42 | 0.16 | 2 | 1.12 (0.91–1.38) | 65 | 0.09 |
 OC and/or HRT use | ||||||||
  Yes | 1 | 0.67 (0.49–0.92) | NA | NA | 1 | 1.04 (0.78–1.40) | NA | NA |
  No | 5 | 1.28 (0.93–1.76) | 31 | 0.21 | 4 | 1.27 (1.02–1.59) | 68 | 0.03 |
 Family history of breast cancer | ||||||||
  Yes | 1 | 1.05 (0.77–1.45) | NA | NA | 0 | NA | NA | NA |
  No | 5 | 1.19 (0.71–2.00) | 72 | 0.01 | 5 | 1.22 (1.01–1.47) | 61 | 0.04 |