OBJECTIVE
Our purpose was to evaluate the association between hemoglobin concentration (Hb) and cognitive ability of children at 4 - 6 years of age in 21 counties/cities in China.
METHODS
A total number of 7331 children born during 1993 - 1996 were randomly selected from 21 counties or cities in Hebei, Jiangsu and Zhejiang provinces. Hb concentration of children were measured followed by three tests including full-scale, verbal and performance intelligence quotient (IQ) test performed by Chinese-Wechsler Intelligence Scale for Children, one year later.
RESULTS
There were a 0.7 point difference in mean verbal scale IQ (P = 0.144) and a 0.9 point difference in both mean performance and full-scale IQ (P = 0.055 and 0.079, respectively) between anemia and non-anemia groups. Compared with children with non-anemia, children with anemia were 1.3-fold more likely to score poorly in verbal IQ and operational IQ (95%CI: 1.1 - 1.6, 1.1 - 1.5, respectively) and 1.4-fold more likely to have had poor scores in full-scale IQ (95%CI: 1.2 - 1.6) after controlled for children's gender, age at intelligence test, region, parity and mother's IQ, education level, occupation. Participants were divided into 5 sub-groups according to Hb concentration of every 20 percentile. Verbal IQ scores of the lowest (Hb < 110 g/L), moderate (117 g/L </= Hb < 122 g/L) and the highest Hb concentration groups (Hb >/= 130 g/L) were 90.6 +/- 18.1, 94.0 +/- 17.6 and 91.0 +/- 16.4, respectively. Performance IQ scores were 102.2 +/- 15.7, 104.6 +/- 14.8 and 100.5 +/- 14.9, respectively. Full-scale IQ scores were 95.9 +/- 17.3, 99.0 +/- 16.4 and 95.2 +/- 15.6, respectively. Children with both low and high hemoglobin levels did poorly in all intelligence tests than children with moderate Hb concentration (P < 0.001). After controlling for confounding factors, children with the lowest concentration were 1.4-fold more likely to have had poor verbal and performance scores than children with moderate Hb concentration (95%CI: 1.1 - 1.7, 1.1 - 1.8, respectively) and 1.5-fold (95%CI: 1.2 - 1.8) more likely to have had poor full-scale scores than those with moderate Hb concentration. The association between high Hb concentration and low IQ scores disappeared in the multivariate model.
CONCLUSION
Low Hb concentration might have adversely affected children's cognitive development.