Table 3

Association between body iron stores and type 2 diabetes mellitus (T2DM) in the included studies

Source

Gender

Comparison

Models

RR (95% CI)

Matched or adjusted covariates


Ferritin as indicators of body iron stores (n = 5)

Jiang et al, 2004, USA [10]

Women

Highest (≥107.2 ng/ml) versus lowest (<21.1 ng/ml) quintile

Model 1a

2.68 (1.75 to 4.11)

Age, ethnicity, fasting status, BMI, FH, PA, smoking, alcohol consumption, menopausal status, glycemic load, intake of total energy, cereal fiber, magnesium, and trans fat, and ratio of polyunsaturated fat to saturated fat

Model 2b

2.61 (1.68 to 4.07)

Additional adjustment for CRP

Forouhi et al, 2007, UKc [11]

Men

Highest (≥135.7 ng/ml) versus lowest (<34.4 ng/ml) quintile

Model 1a

1.97 (1.12 to 3.45)

Age, sex, BMI, FH, PA, smoking, dietary factors (TEI, alcohol consumption, intake of dietary iron, magnesium, and red meat and processed meat, plasma vitamin C)

Model 2b

1.78 (0.99 to 3.19)

Additional adjustment for CRP, fibrinogen, and IL-6

Model 3

1.13 (0.58, 2.19)

Additional adjustment for ALT, GGT, and adiponectin

Women

Highest (≥71.7 ng/ml) versus lowest (<17.8 ng/ml) quintile

Model 1a

2.55 (1.22 to 5.34)

Age, sex, BMI, FH, PA, smoking, dietary factors (TEI, alcohol consumption, intake of dietary iron, magnesium, red meat and processed meat and plasma vitamin C)

Model 2b

2.11 (0.98 to 4.56)

Additional adjustment for CRP, fibrinogen, and IL-6

Model 3

1.08 (0.44, 2.62)

Additional adjustment for ALT, GGT, and adiponectin

Jehn et al, 2007, USA [15]

Both

Highest (≥235.4 ng/ml; median, 354.5 ng/ml) versus lowest (<40.0 ng/ml; median, 20.0 ng/ml)quintile

Model 1a

1.51 (0.98 to 2.31)

Age, study center, ethnicity, smoking, alcohol consumption, and BMI

Model 2

0.81 (0.49 to 1.34)

Additional adjustment for metabolic syndrome components (HDL-C, WC, hypertension, FPG, and TG)

Model 3b

0.79 (0.48 to 1.32)

Additional adjustment for FPI and inflammation score

Le et al, 2009, USA [16]

Men

Highest (>188 ng/ml) versus lowest (<80 ng/ml) quartile

Model 1a

1.79 (1.13 to 2.82)

Age, ethnicity, and BMI

Women

Highest (premenopausal, >60 ng/ml, postmenopausal, >90 ng/ml) versus lowest (premenopausal,<21 ng/ml, postmenopausal,<37 ng/ml) quartile

Model 1a

0.87 (0.37 to 2.03)

Age, ethnicity, and BMI

Rajpathak et al, 2009, USA [17]

Both

Highest (median, 203.7 ng/ml) versus lowest (median, 20.1 ng/ ml) quartile

Model 1a

1.02 (0.60 to 1.74)

Age, sex, ethnicity, and BMI

Model 2

1.65 (0.90 to 3.02)

Additional adjustment for FH, PA, HbA1c, and sTfR

Model 3b

1.53 (0.83 to 2.82)

Additional adjustment for CRP

Model 4

1.61 (0.85 to 3.02)

Additional adjustment for HOMA-IR

Ratio of sTfR to ferritin as indicators of body iron stores (n = 2)

Salonen et al, 1998, Finland [9]

Men

Highest (< 9.4) versus quartile (no data available)

Model 1

2.40 (1.03 to 5.50)

Age, time of examination, place of residence, cigarette smoking, exercise, maximal oxygen uptake, socioeconomic status, height, weight, hip and waist circumferences, glucose, insulin, vitamin E, and serum SFA to (PUFA + MUFA) ratio

Jiang et al, 2004, USA [10]

Women

Highest (<26.7) versus lowest (≥149.4) quintile

Model 1

2.44 (1.61 to 3.71)

Age, ethnicity, fasting status, BMI, FH, PA, smoking, alcohol consumption, menopausal status, glycemic load, intake of total energy, cereal fiber, magnesium, and trans fat, ratio of polyunsaturated fat to saturated fat

Model 2

2.40 (1.55 to 3.71)

Additional adjustment for CRP

sTfR as indicators of body iron stores (n = 1)

Rajpathak et al, 2009, USA [17]

Both

Highest (median, 4.4 mg/l) versus lowest (median, 2.3 mg/l) quartile

Model 1

1.55 (0.93 to 2.57)

Age, sex, ethnicity, and BMI

Model 2

2.26 (1.27 to 4.01)

Additional adjustment for FH, PA, HbA1c, and sTfR

Model 3

2.39 (1.34 to 4.28)

Additional adjustment for CRP

Model 4

2.23 (1.22 to 4.06)

Additional adjustment for HOMA-IR


Abbreviations: ALT, alanine aminotransferase; BMI, body mass index; CRP, C-reactive protein; FH, family history; FPG, fasting plasma glucose; FPI, fasting plasma insulin; GGT, γ-glutamyltransferase; HbA1c, glycated hemoglobin; HDL-C, high-density lipoprotein cholesterol; HOMA-IR, homeostasis model assessment for insulin resistance; IL-6, interleukin-6; MUFA, monounsaturated fatty acids; PA, physical activity; PUFA, polyunsaturated fatty acids; RR, relative risk; SFA, saturated fatty acids; sTfR, soluble transferrin receptor; TEI, total energy intake; TG, triglycerides; WC, waist circumference.

a Estimates used in the meta-analysis of ferritin and T2DM risk in multivariate-adjusted models.

b Estimates used in the meta-analysis of ferritin and T2DM risk in multivariate-adjusted models including inflammatory markers.

c From an ad hoc analysis by Forouhi et al. [11], which used quintiles of ferritin levels as exposure and separately reported for men and women.

Bao et al. BMC Medicine 2012 10:119   doi:10.1186/1741-7015-10-119

Open Data