Table 1.

Characteristics of the individual studies included in this meta-analysis.

References	Location	Age years	Gender	Sample size	Study design	Adjustments	Exposure	Category of exposure	Effect estimates	Diagnostic criteria of MetS	NOS
Bruscato et al. (29)	Brazil	>60	Female	284	Cross-sectional	Age, smoking, years of education, physical activity and dietary fiber.	24 h recall	Iron		IDF	7
								Quartiles 1	1.00
								Quartiles 2	0.65 (0.30, 1.38)
								Quartiles 3	1.33 (0.63, 2.83)
								Quartiles 4	0.72 (0.30, 1.72)
Otto et al. (30)	US	45–84	Both	3,828	Cohort	Energy intake, age, sex, race-ethnicity, education, study center, alcohol intake, physical activity, BMI, fiber intake, cigarette smoking, dietary supplement use, the ratio of polyunsaturated fat intake: saturated fat intake and antioxidant intake	24 h recall	Iron Quintiles 1 Quintiles 2 Quintiles 3 Quintiles 4 Quintiles 5	1.00 1.07 (0.85, 1.36) 1.02 (0.80, 1.30) 1.28 (1.01, 1.63) 1.06 (0.81, 1.40)	AHA	8
Choi et al. (31)	Korea	>19	Both	5,136	Cross-sectional	Age, energy intake and alcohol frequency	24 h recall	Copper Male		NCEP ATP III	8
								Quartiles 1	1.00
								Quartiles 2	0.98 (0.70, 1.37)
								Quartiles 3	0.85 (0.60, 1.20)
								Quartiles 4	0.90 (0.60, 1.37)
								Female
								Quartiles 1	1.00
								Quartiles 2	1.07 (0.80, 1.43)
								Quartiles 3	1.02 (0.74, 1.40)
								Quartiles 4	0.86 (0.58, 1.27)
Li et al. (32)	China	18–65	Both	550	Cross-sectional	Age and sex	3 days recall	Copper		NCEP ATP III	7
								Quartiles 1	1.00
								Quartiles 2	0.75 (0.45, 1.24)
								Quartiles 3	0.65 (0.39, 1.07)
								Quartiles 4	0.61 (0.36, 1.01)
								Selenium
								Quartiles 1	1.00
								Quartiles 2	1.38 (0.89, 2.45)
								Quartiles 3	0.81 (0.54, 1.49)
								Quartiles 4	0.82 (0.46, 1.30)
Motamed et al. (33)	Iran	35–65	Both	3,800	Cross-sectional	Sex, age, physical activity level, smoking, past medical history, energy intake and BMI	24 h recall	Iron		IDF	7
								Quintiles 1	1.00
								Quintiles 2	1.15 (0.90, 1.40)
								Quintiles 3	1.24 (0.90, 1.50)
								Quintiles 4	1.24 (1.00, 1.50)
								Quintiles 5	1.12 (0.90, 1.40)
								Copper
								Quintiles 1	1.00
								Quintiles 2	1.25 (1.00, 1.50)
								Quintiles 3	1.33 (1.06, 1.60)
								Quintiles 4	1.16 (0.90, 1.40)
								Quintiles 5	1.15 (0.90, 1.40)
								Selenium
								Quintiles 1	1.00
								Quintiles 2	0.96 (0.70, 1.10)
								Quintiles 3	0.85 (0.60, 1.04)
								Quintiles 4	0.92 (0.70, 1.10)
								Quintiles 5	0.78 (0.60, 0.90)
Suarez-Ortegón et al. (34)	Colombia	11–16	Both	1,311	Cross-sectional	Age, BMI, socioeconomic status, and intakes of fat, carbohydrates, protein and ascorbic acid	24 h recall	Copper Males		Ferranti	7
								Tertiles 1	1.00
								Tertiles 2	/
								Tertiles 3	0.84 (0.32, 2.19)
								Females
								Tertiles 1	1.00
								Tertiles 2	/
								Tertiles 3	0.77 (0.30, 1.82)
Wei et al. (35)	China	>18	Both	2,069	Cross-sectional	Age, sex, cigarette smoking, alcohol drinking, nutritional supplementary, activity level, dietary energy intake, fiber intake and protein intake	FFQ	Selenium Quartiles 1 Quartiles 2 Quartiles 3 Quartiles 4	1.00 0.60 (0.43, 0.86) 0.82 (0.58, 1.17) 0.72 (0.46, 1.14)	AHA	7
Bulka et al. (36)	Spain	18–74	Both	15,051	Cross-sectional	Energy intake, age, gender, and Hispanic/Latino background	24 h recall	Copper Below EAR Normal	1.00 0.81 (0.69, 0.95)	AHA	8
Qu et al. (37)	China	20–75	Both	9,108	Cross-sectional	Age, sex, BMI, physical activity, drinking, and smoking	FFQ	Copper		IDF	8
								Quartiles 1	1.00
								Quartiles 2	0.95 (0.82, 1.11)
								Quartiles 3	0.85 (0.74, 0.99)
								Quartiles 4	0.81 (0.70, 0.94)
Zhu et al. (39)	China	>18	Both	3,099	Cross-sectional	Age, sex, income, physical activity level, intentional physical exercise, smoking status, alcohol use and dietary total energy intake	24 h and 3 days recall	Iron		NCEP ATP III	8
								Quartiles 1	1.00
								Quartiles 2	1.37 (1.06, 1.78)
								Quartiles 3	1.47 (1.11, 1.94)
								Quartiles 4	1.59 (1.15, 2.20)
Vieira et al. (38)	Brazil	>18	Both	591	Cross-sectional	Physical activity, gender, alcohol consumption, household per capita income, BMI, high-sensitivity C-reactive protein, age, smoking status, race, total energy intake, misreporting, saturated fat and vitamin C intakes	24 h recall	Iron Quintiles 1 Quintiles 2 Quintiles 3 Quintiles 4 Quintiles 5	1.00 0.83 (0.36, 2.70) 1.34 (0.63, 2.84) 0.52 (0.26, 1.04) 1.14 (0.54, 2.40)	NCEP ATP III	7
Esfandiar et al. (40)	Iran	>18	Both	4,654	Cohort	Age, sex, baseline BMI, educational level, smoking status, total energy intake, fiber, saturated fat, sodium, vitamin C and magnesium intakes	FFQ	Iron Quartiles 1 Quartiles 2 Quartiles 3 Quartiles 4	1.00 0.97 (0.79, 1.19) 1.10 (0.81, 1.49) 2.04 (0.97, 4.28)	NCEP ATP III	7
Zhu et al. (41)	China	>18	Both	5,323	Cross-sectional	Age, sex, region, years of education, physical activity level, intended physical exercises, smoking status, alcohol use and daily energy intake, zinc and magnesium	24 h and 3 days recall	Iron Quartiles 1 Quartiles 2 Quartiles 3 Quartiles 4	1.00 1.35 (1.10, 1.65) 1.47 (1.15, 1.88) 1.60 (1.21, 2.11)	NCEP ATP III	8
Batista et al. (42)	Brazil	14–19	Both	327	Cross-sectional	Sex, age, maternal education, family income, physical activity, and alcohol consumption	24 h recall	Copper		Cooks	7
								Tertiles 1	1.00
								Tertiles 2	1.49 (0.56, 4.09)
								Tertiles 3	0.87 (0.28, 2.70)
								Selenium
								Tertiles 1	1.00
								Tertiles 2	2.17 (0.66, 7.36)
								Tertiles 3	0.81 (0.30, 2.19)