Table 2 Meta-analyses for zinc concentration (mg/L)

All studies

243

37,614

2.57 (2.50, 2.65)

NA

NA

All studies without outliers

240

37,266

2.58 (2.49, 2.67)

Key studies^c

31

4309

2.26 (2.00, 2.51)

Infant age

0–5.9 months

198

28,267

2.82 (2.73, 2.91)

< 0.001

< 0.001

6–11.9 months

56

4280

1.18 (1.05, 1.32)

12–35.9 months

12

411

0.76 (0.54, 0.98)

Unspecified

27

2619

2.12 (1.80, 2.43)

Infant age, key studies ^c

0–5.9 months, healthy, term, exclusively breastfed

25

3238

2.73 (2.44, 3.02)

< 0.001

NA

6–11.9 months, healthy, term

17

1387

0.96 (0.79, 1.13)

12–35.9 months, healthy, term

5

190

0.76 (0.30, 1.23)

Lactation stage

Colostrum

58

4689

6.39 (5.84, 6.95)

< 0.001

< 0.001

Colostrum/transitional milk

24

1099

4.58 (3.43, 5.73)

Transitional milk

61

3310

3.73 (3.51, 3.96)

Transitional/mature milk

18

741

3.04 (1.62, 4.45)

Mature milk

186

25,031

1.98 (1.88, 2.08)

Unspecified/Mixed

25

2909

2.18 (1.48, 2.88)

Maternal/infant health

Healthy

137

23,192

2.58 (2.47, 2.69)

0.456

0.151

With condition

9

1222

3.05 (1.81, 4.29)

Unspecified/Mixed

104

13,450

2.76 (2.60, 2.91)

Maternal age

Adults

109

18,071

2.96 (2.75, 3.18)

< 0.001

< 0.001

Adolescents

4

557

1.40 (1.28, 1.53)

Unspecified/Mixed

131

18,856

2.57 (2.44, 2.69)

Gestation

Term

102

14,040

2.75 (2.60, 2.90)

0.280

0.045

Preterm

26

2183

3.37 (2.26, 4.47)

Unspecified/Mixed

137

21,537

2.53 (2.40, 2.67)

Breastfeeding practices

Exclusive

44

5636

2.58 (2.28, 2.87)

< 0.001

< 0.001

Mixed

25

3894

1.45 (1.17, 1.74)

Unspecified

178

27,885

2.84 (2.74, 2.95)

Zinc supplementation

Supplemented

13

1596

2.06 (1.72, 2.41)

0.012

0.018

Not supplemented

48

7045

2.63 (2.36, 2.91)

Unspecified/Mixed

195

28,795

2.57 (2.48, 2.65)

Nutritional status

Good

26

3996

3.22 (2.62, 3.83)

0.152

0.067

Poor

9

1141

2.64 (2.13, 3.16)

Unspecified/Mixed

211

32,762

2.51 (2.44, 2.59)

Country income category

Low

8

961

2.31 (1.72, 2.90)

< 0.001

< 0.001

Lower-middle

44

5931

2.38 (2.21, 2.55)

Upper-middle

83

12,706

2.92 (2.75, 3.09)

High

116

15,867

2.49 (2.28, 2.70)

Unspecified/Mixed

4

1960

3.04 (1.97, 4.10)

Continent

Africa

32

3931

3.03 (2.76, 3.3)

< 0.001

< 0.001

Asia

84

15,477

2.78 (2.61, 2.95)

Australasia/Oceania

5

579

1.75 (0.86, 2.64)

Europe

54

7653

2.77 (2.48, 3.06)

North America

46

6321

1.93 (1.7, 2.17)

South America

32

3336

2.43 (2.27, 2.58)

Unspecified/Mixed

2

128

4.17 (2.5, 5.84)

Measurement method

AAS^d

92

13,314

2.91 (2.67, 3.14)

0.001

0.001

FAAS^d

51

6577

2.60 (2.46, 2.74)

ICP-AES^d

35

5681

2.39 (2.27, 2.51)

ICP-MS^d

53

10,210

2.55 (2.19, 2.91)

Other

12

2082

3.07 (2.55, 3.59)