Table 2 Association between dietary and supplemental iron intakes and type 2 diabetes mellitus (T2DM) in the included studies

Jiang et al, 2004, USA [20]

Men

Dietary total iron intake: highest (median 34.2 mg/day) versus lowest (median 11.1 mg/day) quintile

1.16 (0.92 to 1.47)

Age, BMI, FH, PA, cigarette smoking, alcohol consumption, TEI, intakes of trans fat, cereal fiber, magnesium, whole grains, vegetables, fruit, ratio of polyunsaturated fat to saturated fat intake, glycemic load, and multivitamin use

Dietary heme iron intake: highest (median 1.9 mg/day) versus lowest (median 0.8 mg/day) quintile

1.28 (1.02 to 1.61)

Lee et al, 2004, USA [24]

Women

Dietary non-heme iron intake: highest (median 20.8 mg/day) versus lowest (median 6.5 mg/day) quintile

0.80 (0.64 to 1.01)

Age, BMI, WHR, PA, cigarette smoking status, alcohol consumption, education, marital status, residential area, hormone replacement therapy, TEI, intakes of animal fat, vegetable fat, cereal fiber, dietary magnesium, dietary non-heme iron, dietary heme iron, and supplemental iron

Dietary heme iron intake: highest (median 2.2 mg/day) versus lowest (median 0.5 mg/day) quintile

1.28 (1.04 to 1.58)

Supplemental iron: highest (≥30 mg/day) versus lowest (0 mg/day) intake

1.16 (0.92 to 1.46)

Song et al, 2004, USA [23]

Women

Dietary total iron intake: highest (median 33.8 mg/day) versus lowest (median 10.0 mg/day) quintile

1.13 (0.93 to 1.37)

Age, BMI, PA, FH, smoking status, alcohol consumption, TEI, dietary intakes of fiber, magnesium, and total fat, glycemic load

Dietary heme iron intake: highest(median 1.55 mg/day) versus lowest (median 0.59 mg/day) quintile

1.46 (1.20 to 1.78)

Rajpathak et al, 2006, USA [21]

Women

Dietary total iron intake: highest (median 14.0 mg/day) versus lowest (median 8.0 mg/day) quintile

1.02 (0.91 to 1.15)

Age, BMI, FH, PA, smoking status, alcohol consumption, postmenopausal hormone use, multivitamin use, TEI, intakes of cereal fiber and magnesium, caffeine, and trans fat (total iron, ratio of polyunsaturated to saturated fat, glycemic load, additional adjustment for intakes of whole grains, fruits and vegetables (heme iron), and additional adjustment for red meat intake (supplemental iron)

Dietary heme iron intake: highest (median 1.9 mg/day) versus lowest (median 0.8 mg/day) quintile

1.28 (1.14 to 1.45)

Supplemental iron intake: highest (median 22.0 mg/day) versus lowest (median 0 mg/day) quintile

0.96 (0.84 to 1.10)

Shi et al, 2010, China [30]

Both

Dietary heme iron intake: highest (median 4.4 mg/day) versus lowest (median 0.1 mg/day) quartile

9.84 (1.41 to 68.75)

Age, gender, BMI, central obesity, hypertension, FH, PA, sedentary behavior, cigarette smoking, alcohol consumption, TEI, intakes of fat, fiber and magnesium, education, income, and job