Long-term Health Effects of the Atomic Bombings in Japan

Catherine Dong
April 15, 2016

Submitted as coursework for PH241, Stanford University, Winter 2016


In 1945, near the end of World War II, the United States launched what would be the only use of nuclear weapons for warfare in history. On August 6, the U.S. dropped a uranium gun-type bomb on the Japanese city of Hiroshima, calling for Japan's surrender. Three days later, the U.S. dropped another atomic bomb on the city of Nagasaki. These two bombings killed at least 129,000 people. About half of these deaths occurred occurred within one day of each of the bombings. In the following months, burns, radiation sickness, and other injuries killed thousands more. Beyond this are additional long-term effects due to the massive amounts of radiation released by the detonation of these atomic bombs. In this report, we will examine the long-term biological effects of the atomic bombs on the incidence of cancer, prenatal disorders, and other diseases in Japan.

Gestational Age (Weeks) Number of Subjects Regression Coefficient
(IQ change per Gy)
Standard Error
0-7 269 -0.057 0.061
8-15 340 -0.121 0.039
16-25 480 -0.207 0.042
26+ 576 -0.033 0.055
Total 1673 -0.155 0.023
Table 1: Regression coefficients of IQ scores for fetuses exposed to radiation in the uterus reported by Otake et al. [2]

Cancer Incidence and Mortality

Since 1950, The Radiation Effects Research Foundation (RERF) has been studying a cohort of about 120,000 Hiroshima and Nagasaki residents who were survivors of the atomic bombings. The RERF's most significant finding was that the radiation from the atomic bombs has led to an increased risk of cancer mortality throughout the lives of those exposed. [1] Specifically, cancer mortality for stomach, lung, liver, colon, breast, ovary, and other major sites was found to be significantly higher. [1] Furthermore, the rates of cancer increases approximately linear to the dosage of radiation exposure, and those exposed as children had a higher risk of being diagnosed with cancer. [1] This reveals that the atomic bombings in Japan had effects that were far more pernicious than the immediate injury-related deaths. Thousands of civilians in the exposed areas carry an increased risk of cancer for the rest of their lives.

Prenatal Effects

A study by Otake et al. revealed that there was increased incidence of severe mental retardation among prenatally exposed survivors of the atomic bombings. [2] The highest risk was for fetuses that were exposed to the radiation 8-15 weeks after fertilization. Another study by Schull et al. examined the intelligence test scores of children exposed prenatally to atomic bomb radiation. [3] While there was no significant effect on intelligence for those exposed 0-7 weeks after fertilization, those exposed 8-15 weeks after fertilization again showed slightly decreased scores on the intelligence test (Table 1), which was consistent with the study on mental retardation. In addition, Yamazaki et al. found that exposure to atomic bomb radiation in utero was related to a significant increase in perinatal mortality and vulnerability of the fetus's brain to injury. [4] Consistent with the other studies, they found that the most critical period in fetal brain development was 8-15 weeks after fertilization. This period of fetus development corresponds to high brain cell proliferation and development. Children exposed to radiation during this period showed increased risk of mental retardation, small head size, seizures, and poor performance in school. All together, these studies reveal that the atomic bombings of Japan impacted the well-being of not only the individuals who were directly exposed to the explosions or radiation but also potentially had negative consequences on the next generation.

Other Diseases

A correlation has been found between radiation exposure and increased risk of non-neoplastic diseases related to the circulatory, respiratory, and digestive systems. [1] However, further studies must be conducted in order to demonstrate a causal relationship.

© Catherine Dong. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] K. Ozasa et al., "Studies of the Mortality of Atomic Bomb Survivors, Report 14, 1950-2003: An Overview of Cancer and Noncancer Diseases," Radiat. Res 177, 229 (2012).

[2] M. Otake, W. J. Schull, and H. Yoshimaru, "Brain Damage Among the Prenatally Exposed," J. Radiat. Res. 32 (Suppl. 1), 249 (1991).

[3] W. J. Schull and M. Otake, "Cognitive Function and Prenatal Exposure to Ionizing Radiation," Teratology 59, 222 (1999).

[4] J. N. Yamazaki and W. J. Schull, "Perinatal Loss and Neurological Abnormalities Among Children of the Atomic Bomb," J. Am. Med. Assoc. 264, 605 (1990).