Table 3

Studies by setting, directionality and quality grading

SettingDirection of findingsNumber of studies (%)Quality grading (%)
Developing countries (n=13)No association between IQ and BF6 (46)A—0 (0)
B—2 (33.3)
C—4 (66.6)
Positive association between IQ and BF4 (30)A—1 (25)
B—0 (0)
C—3 (75)
Initial positive association which became negative after adjustment for confounders.2 (15)A—0 (0)
B—2 (100)
C—0 (0)
Initial positive association weakened after adjustment for confounders but remained statistically significant1 (8)A—1 (100)
B—0 (0)
C—0 (0)
Developed countries (n=71)No association between IQ and BF15 (21)A—4 (26.6)
B—7 (46.6)
C—4 (26.6)
Positive association between IQ and BF24 (34)A—9 (37.5)
B—7 (29.2)
C—8 (33.3)
Initial positive association which became negative after adjustment for confounders.16 (22.5)A—6 (37.5)
B—6 (37.5)
C—4 (25)
Initial positive association weakened after adjustment for confounders but remained statistically significant16 (22.5)A—13 (81.25)
B—2 (12.5)
C—1 (6.25)
  • Developing: Refs. 15 ,21 ,33–36 ,38 ,63 ,69 ,72 ,73 ,97 ,100

  • Developed: Refs. 9 ,13 ,22–32 ,37 ,39–62 64–71 74–96 ,98 ,99 ,101

  • BF, breastfeeding.