Background
The Great East Japan Earthquake that occurred on 11 March 2011 and the Fukushima Daiichi nuclear disaster forced people to evacuate their hometowns with notice, caused them to change their lifestyle to fit a completely new situation, and produced anxiety about radiation. In response to concerns about the effects these factors could have on health, the Comprehensive Health Check (CHC), 1 of 4 detailed surveys of the Fukushima Health Management Survey (FHMS), was implemented to support the early detection and treatment of disease as well as the prevention of lifestyle-related diseases, such as heart disease and cerebrovascular disease.
Japan experienced atomic bombings in Hiroshima and Nagasaki in 1945. In 1947, the Atomic Bomb Casualty Commission (ABCC) was established to investigate the health impacts on atomic bomb (A-bomb) survivors. Later, a large-scale cohort study of survivors was started in order to investigate the long-term stochastic effects of radiation. The ABCC had continued follow-up surveys through the present time [
1‐
3]. In April 1986, the worst nuclear disaster in human history occurred at the Chernobyl Nuclear Power Plant. The accident released a large quantity of radioactive material into the atmosphere. The USSR Ministry of Health started the Russian National Medical and Dosimetric Registry in June the same year to resister residents exposed to radiation. However, an epidemiologic study evaluating long-term radiation effects on public health was unfortunately not implemented soon enough after the accident [
4].
The primary purposes of the FHMS are to monitor the long-term health of residents, promote their future well-being, and determine whether long-term low-dose radiation exposure has health effects. The FHMS consists of a basic survey and 4 detailed surveys, namely, thyroid ultrasound examination, comprehensive health check, a mental health and lifestyle survey, and a pregnancy and birth survey [
5]. Many evacuees from the government-designated evacuation zone were forced to change their lifestyle, diet, exercise, and other personal habits. Some could not receive adequate health checks, and some had anxieties about their health [
6]. The CHC attempts to review their health information, assess the incidence of various diseases, and improve their health status. Here we focused on changes in red blood cell count before and after the disaster.
Results and discussion
On implementing the CHC, we expected that there were no individuals with the risk of cytopenia according to the results of estimation of external dose in the FHMS [
8,
9]. Furthermore, because the comparable items in the peripheral blood count before and after the disaster were RBC, Hb, and Ht, we analyzed the change in those items. Changes in lifestyle among evacuees caused increases in body weight and blood pressure [
10]. Therefore, we expected that it would cause polycythemia as well. The standard values for peripheral blood in the CHC are as follows: RBC 400–579 × 10
4/μL, Hb 13.1-17.9 g/dL, and Ht 38.0-54.9% in men; RBC 370–549 × 10
4/μL, Hb 12.1-15.9 g/dL, and Ht 33.0-47.9% in women. As for the diagnosis of polycythemia, one of these items is beyond the standard value.
First, RBC, Hb, and Ht significantly increased in both men and women evacuees (Table
2). Furthermore, age-adjusted
p value for comparing the changes of these items in the evacuee group to those in the non-evacuee group between before and after the earthquake was significant (Table
2). Next we performed a multivariate analysis to find whether the evacuation was an independent factor for an increase in Hb in the presence of smoking, one of the important causes of polycythemia, and obesity and weight gain, which were already reported to be related to the evacuation [
9]. The evacuation was significantly associated with increased Hb levels after adjustment for age, gender, smoking status, excess ethanol intake, BMI, and baseline Hb level (β = 0.16,
p < 0.001). In the present study, mean levels of BMI of the participants increased from 23.6 kg/m
2 to 24.0 kg/m
2 before and after the disaster (
p < 0.001). The association between evacuation and increased Hb levels was attenuated after further adjustment for change in BMI before and after the disaster, but it remained statistically significance (β = 0.11,
p < 0.001). Furthermore, increasing of Hb levels in the present study might not be influenced by change in proportion of smoking status because the proportion of smokers decreased after the disaster in both evacuees and non-evacuees; from 12.8% to 11.9% for evacuees and from 10.2% to 8.4% for non-evacuees.
Table 2
Changes in RBC, Hb, and Ht according to evacuation status
Men | (-) | 1349 | 463.1 | | 461.3 | -1.8 | 0.02 | 14.46 | | 14.57 | 0.10 | <0.0001 | 43.57 | | 43.45 | -0.12 | 0.11 |
(+) | 3278 | 472.7 | | 479.2 | 6.5 | <0.0001 | 14.77 | | 15.05 | 0.28 | <0.0001 | 44.34 | | 44.74 | 0.40 | <0.0001 |
| | |
p*
| | <0.0001 | | |
p*
| | <0.0001 | | |
p*
| | <0.0001 | |
Women | (-) | 1923 | 434.5 | | 432.2 | -2.3 | <0.0001 | 13.04 | | 13.15 | 0.11 | <0.0001 | 40.00 | | 39.95 | -0.05 | 0.31 |
(+) | 4168 | 439.6 | | 443.1 | 3.5 | <0.0001 | 13.18 | | 13.40 | 0.22 | <0.0001 | 40.42 | | 40.74 | 0.33 | <0.0001 |
| | |
p*
| | <0.0001 | | |
p*
| | <0.0001 | | |
p*
| | <0.0001 | |
In this study the standard values of obesity and the significant weight gain are a BMI of 25 kg/m
2 or more and an increase in BMI of 1 kg/m
2 or more, respectively. We also analyzed age-adjusted
p values for comparing the changes in Hb in the evacuee group to those in the non-evacuee group between before and after the earthquake because the value of Hb is a representative index of polycythemia (Table
3). In men, the evacuation significantly influenced an increase in Hb regardless of smoking status, and the group that did not smoke showed a more significant increase. In the relationship between the changes in Hb and BMI or increase in BMI, the evacuation had a significant influence on the group with BMI less than 25 kg/m
2 and increase of less than 1 kg/m
2 in BMI. In women, the evacuation significantly influenced an increase in Hb in the group that did not smoke. The evacuation increased the value of Hb regardless of obesity, and the increase in Hb was significantly higher in the group with BMI less than 25 kg/m
2. Furthermore, the evacuation was followed by a significant increase in Hb in the group with less than 1 kg/m
2 increase in BMI. These results revealed that life as an evacuee leads to increase in Hb. However, what is especially important is whether an incidence of polycythemia in the evacuee group, but not in the non-evacuee group, significantly increased after the disaster. Prevalence of polycythemia before and after the disaster were 0.79% and 1.16% for the non-evacuees (
p = 0.10) and 0.89% and 1.54% for the evacuees (
p < 0.001), respectively. Then, we further analyzed the prevalence of polycythemia stratified by smoking status or obesity, the tendency was virtually unchanged (Table
4). Among smokers, prevalence of polycythemia before and after the disaster were 1.19% and 1.79% for the non-evacuees (
p = 0.50) and 1.89% and 3.67% for the evacuees (
p < 0.01), and among non-smokers, those of polycythemia were 0.75% and 1.09% for the non-evacuees (
p = 0.16) and 0.74% and 1.23% for the evacuees (
p < 0.001), respectively. Among obese, prevalence of polycythemia before and after the disaster were 1.06% and 1.59% for the non-evacuees (
p = 0.36) and 1.48% and 2.45% for the evacuees (
p < 0.01), and among non-obese, those of polycythemia were 0.69% and 0.99% for the non-evacuees (
p = 0.23) and 0.61% and 1.12% for the evacuees (
p < 0.001), respectively. Based on these results, we suggest that the evacuation is an independent factor for polycythemia regardless of smoking status, obesity, or weight gain, while an logistic regression analysis showed the association between evacuation and newly-developing polycythemia did not reach statistical significance; the multivariable adjusted odds ratio for evacuation is 1.11 (95% confidence interval; 0.71-1.73).
Table 3
Influence of the evacuation on changes of Hb in relation to smoking, obesity, and weight gain
Men | Smoking (-) | 3,579 | 0.11 | 0.29 | <0.0001 |
Smoking (+) | 1,048 | 0.09 | 0.27 | 0.008 |
BMI <25 kg/m2
| 3,180 | 0.10 | 0.30 | <0.0001 |
BMI 25 ≧ kg/m2
| 1,447 | 0.13 | 0.24 | 0.08 |
Change in BM < 1 kg/m2
| 2,981 | 0.03 | 0.15 | 0.006 |
Change in BM ≧ 1 kg/m2
| 1,646 | 0.44 | 0.46 | 0.89 |
Women | Smoking (-) | 5,851 | 0.12 | 0.22 | <0.0001 |
Smoking (+) | 240 | -0.04 | 0.13 | 0.12 |
BMI <25 kg/m2
| 4,229 | 0.12 | 0.22 | 0.0002 |
BMI 25 ≧ kg/m2
| 1,862 | 0.10 | 0.21 | 0.02 |
Change in BM < 1 kg/m2
| 4,444 | 0.09 | 0.17 | 0.002 |
Change in BM ≧ 1 kg/m2
| 1,647 | 0.22 | 0.31 | 0.13 |
Table 4
Influence of the evacuation on prevalence of polycythemia in relation to smoking and obesity
Total | | Evaculation (-) | 3,272 | 26 (0.79) | 38 (1.16) | 0.10 |
| Evaculation (+) | 7,446 | 66 (0.89) | 115 (1.54) | <0.001 |
Obese | + | Evaculation (-) | 945 | 10 (1 .06) | 1 5 (1.59) | 0.36 |
Evaculation (+) | 2,364 | 35 (1 .48) | 58 (2.45) | <0.01 |
- | Evaculation (-) | 2,327 | 6 (0.69) | 23 (0.99) | 0.23 |
Evaculation (+) | 5,082 | 31(0.61) | 57 (1.12) | <0.001 |
Smoking | + | Evaculation (-) | 335 | 4 (1.19) | 6 (1.79) | 0.50 |
Evaculation (+) | 953 | 18 (1 .89) | 35 (3.67) | 0 < 0.01 |
- | Evaculation (-) | 2,973 | 22 (0.75) | 32 (1.09) | 0.16 |
Evaculation (+) | 6,493 | 48 (0.74) | 80 (1.23) | <0.001 |
Common causes of polycythemia are polycythemia vera (myeloproliferative disease), secondary polycythemia caused by diseases such as pulmonary heart disease that induce a chronic lack of oxygen or an erythropoietin-producing tumor, and relative polycythemia or stress-induced polycythemia. The mechanism of stress-induced polycythemia is unknown, and it is usually diagnosed in middle-aged men who smoke, are obesity, and have hypertension, or hyperuricemia. Although dehydration induced by use of diuretic for hypertension might affect Hb level, the difference of such a factor between evacuees and non-evacuees could not be clarified. To our knowledge, this is the first report showing that evacuation is a cause of polycythemia. Even in the group that was not evacuated, the value of Hb before and after the disaster increased significantly in both men and women (Table
2). Some kind of stress induced by the disaster might be causing the increase in Hb in this group.
The increase of lifestyle-related disease was expected because obesity, weight gain, and high blood pressure were shown to occur in evacuees after the disaster, and this investigation revealed that life as an evacuee causes polycythemia. Here we suggest that periodic health checkups and lifestyle guidance for evacuees in the future is very important.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
AS and TO designed the study and contributed to writing the manuscript. TO also performed data collection and statistical analysis. MH, AO, HS, YK, HS, AT, GK, KO, and SY contributed to planning the health screening program. SY, KK, and MA contributed to scientific review. All authors read and approved the final manuscript.