BACKGROUND: Residential greenness has been reported to be positively associated with health benefits for children, including improved cognitive function. We investigated the association between the intelligence quotient (IQ) of 6-year-old children in Seoul, South Korea and surrounding greenness currently and during the mothers' pregnancy. We also analyzed whether these effects differed by the type of greenness, such as natural or built greenness.

METHODS: This study considered 189 mother-child dyads from the Environment and Development of Children Cohort study, who lived in Seoul during the prenatal period and when the child was 6 years old. We defined surrounding greenness using Landsat image data from Korean Arirang satellite images with buffers within 100 m - 2000 m of the radius of each participant's residential address. We separately analyzed two types of greenness, namely natural and built greenness. The children's IQ (total, verbal, and performance IQ) was measured using the Korean Educational Developmental Institute's Wechsler Intelligence Scale for Children.

RESULTS: Prenatal exposure to built greenness in 500 m and 1000 m buffers was associated with children's total IQ in a full model [difference in IQ (95% CI): 3.46(0.68, 6.24) and 3.42 (0.53, 6.31) per interquartile increase in proportion of greenness]. However, postnatal exposure to built greenness in all buffers was associated in children's total IQ. We found a stronger association between children's total IQ and built greenness rather than natural greenness.

CONCLUSIONS: We found that 6-year-old children tended to score higher on total IQ if they lived in greener neighborhoods. The results provide further evidence of the health benefits of greenness and provide support for urban planning and public health to build healthy urban cities for children and pregnant women.