Technical Report No. 7-86
Effect on intelligence of prenatal exposure to ionizing radiation
Schull WJ, Otake MEditor’s note: Publications based on this report were published in Epidemiology and Quantitation of Environmental Risk in Humans from Radiation and Other Agents. Ed by Castellani A. New York, Plenum Press, 1985. pp 515-36 (Proceedings of a NATO ASI, San Miniato, Italy, 2-11 September 1984), and Oyo Tokeigaku – Jpan J Applied Statistics 15:163-80, 1986.
Summary
Analysis of intelligence test scores at 10-11 years of age of individuals exposed prenatally to the atomic bombing of Hiroshima and Nagasaki has revealed the following: 1) For those individuals exposed in the first eight weeks after fertilization or after the 25th week, there is no evidence of a radiation-related effect on intelligence; 2) The mean test scores but not the variances are significantly heterogeneous among exposure categories for individuals exposed at 8-15 weeks after fertilization, and to a lesser extent those exposed at 16-25 weeks; 3) The regression of intelligence score on estimated fetal tissue dose is linear or linear-quadratic for the 8-15 week group and possibly linear for the 16-25 week group; 4) The cumulative distributions of test scores suggest a progressive shift downwards in the scores with increasing exposure; and 5) Within the group most sensitive to the occurrence of clinically recognizable, severe mental retardation, individuals exposed 8 to 15 weeks after fertilization, the diminution in intelligence score under the linear-quadratic model is 21-27 points at 1 gray (Gy =100 cGy = 100 rad). The effect is somewhat greater when the controls receiving less than 0.01 Gy are excluded, 33-41 points at 1 Gy; but the two estimates are not statistically significantly different.
Analysis of intelligence test scores at 10-11 years of age of individuals exposed prenatally to the atomic bombing of Hiroshima and Nagasaki has revealed the following: 1) For those individuals exposed in the first eight weeks after fertilization or after the 25th week, there is no evidence of a radiation-related effect on intelligence; 2) The mean test scores but not the variances are significantly heterogeneous among exposure categories for individuals exposed at 8-15 weeks after fertilization, and to a lesser extent those exposed at 16-25 weeks; 3) The regression of intelligence score on estimated fetal tissue dose is linear or linear-quadratic for the 8-15 week group and possibly linear for the 16-25 week group; 4) The cumulative distributions of test scores suggest a progressive shift downwards in the scores with increasing exposure; and 5) Within the group most sensitive to the occurrence of clinically recognizable, severe mental retardation, individuals exposed 8 to 15 weeks after fertilization, the diminution in intelligence score under the linear-quadratic model is 21-27 points at 1 gray (Gy =100 cGy = 100 rad). The effect is somewhat greater when the controls receiving less than 0.01 Gy are excluded, 33-41 points at 1 Gy; but the two estimates are not statistically significantly different.