Brief Reports
Metabolic syndrome and central obesity in domestic migrant radiation decontamination workers
2020 Volume 2 Issue 1 Article ID: 2020-0009-BR
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2020 Volume 2 Issue 1 Article ID: 2020-0009-BR
Objectives: To examine the association between metabolic syndrome or its components, including central obesity, and domestic migration in the radiation decontamination workers. Methods: This study was conducted on male workers who engaged in decontamination work at Iitate Village, Fukushima Prefecture, Japan. Of 125 workers, 91 answered a question about their domestic migration. Metabolic syndrome was assessed based on the criteria of the Japanese Committee for the Diagnostic Criteria of Metabolic Syndrome, using their health checkup data from February through June 2017. We used logistic regression analysis to examine the associations of metabolic syndrome and its components with migration status. Results: Of the 91 workers, 32 (35.1%) were migrant workers. The age-adjusted odds ratios of domestic migrant workers for metabolic syndrome, central obesity, hypertension, glucose intolerance, and dyslipidemia were 1.75 (95% confidence interval (CI): 0.60–5.10), 2.45 (95% CI: 1.01–5.94), 1.07 (95% CI: 0.39–2.94), 0.40 (95% CI: 0.13–1.25), and 0.87 (95% CI: 0.34–2.20), respectively, compared to non-migrant workers. Conclusions: Domestic migrant radiation decontamination workers have a high prevalence of central obesity compared with non-migrant workers. Further longitudinal investigation is necessary for health promotion in domestic migrant workers.
In March 2011, the Fukushima Daiichi Nuclear Power Plant accident, which followed the Great East Japan Earthquake and its tsunami, spread a large amount of radioactive material into the surrounding areas. To reduce radioactive exposure, the Japanese government determined to make a high effort in decontamination. Decontamination work includes removing soil, weeds, and fallen leaves and washing houses and roads. Due to the rapidly growing employment offers for radiation decontamination workers, many people migrated to Fukushima Prefecture from other prefectures to work as decontamination workers. The total number of domestic migrant and non-migrant radiation decontamination workers has been reported to be 10,000–20,000 in 20161). Generally, domestic migrant workers are not only exposed to occupational risks, but their access to healthcare was also poor, along with poor healthcare-seeking behaviours2) and more health problems3), compared to non-migrant workers. In fact, one descriptive study has shown a high incidence of underlying dyslipidemia, diabetes mellitus, and hypertension among hospitalized radiation decontamination workers4). However, little knowledge is available on the primary health conditions of decontamination workers.
Metabolic syndrome is a group of metabolic disorders characterized by central obesity, hypertension, glucose intolerance, and dyslipidemia and is a major primary health threat. In particular, central obesity is a critical factor in metabolic syndrome, which reflects increases in visceral fat, the root of the syndrome5). Central obesity is the easiest parameter of self-awareness among metabolic syndrome components. Insight into the metabolic syndrome and central obesity among domestic migrant workers would improve primary prevention strategies. A previous study by Bi et al. examined the prevalence of metabolic syndrome in domestic migrant workers and compared with the general population in Asia6). However, few studies have examined the relationship between metabolic syndrome or central obesity and domestic migration in the same occupation. The prevalence of metabolic syndrome and lifestyle habits are different among occupations7,8). Therefore, it is necessary to investigate the relationship between metabolic syndrome and domestic migrants in the same occupation.
The purpose of this is to examine the association between metabolic syndrome or its components, including central obesity, and domestic migration in the radiation decontamination workers.
This cross-sectional study was conducted in Iitate village, Fukushima Prefecture, Japan, which is about 40 km northwest of Fukushima Daiichi Nuclear Power Plant. All residents had been forced to evacuate from the village because of high radioactive contamination after the Fukushima Daiichi Nuclear Power Plant accident, although they were not victims of the earthquake or tsunami. Most decontamination plans in the village had been completed and, in March 2017, the evacuation order for the village was withdrawn except for one area, which still has high levels of radiation9).
SubjectsThis study was conducted using the data of decontamination workers who belonged to a company that operated decontamination work in Iitate village, Fukushima Prefecture. From February through June 2017, a total of 125 male radiation decontamination workers underwent a mandatory health checkup performed every 6 months. Of the 125 decontamination workers, 28 workers did not give consent for this study. Of the remaining 97 decontamination workers, we excluded 6 workers who did not answer the question about migration. Finally, 91 workers were included for analysis. The response and effective response rates were 77.6% and 72.8%, respectively.
All study subjects were term-limited workers from April 2017 through December 2017, when the decontamination project had taken place. The company had an occupational health physician and a safety and hygiene officer. The occupational health physician visited the company at least once a month to provide health guidance. As both domestic migrant and non-migrant workers had the same employment contract, there was little difference between these workers in the occupational healthcare system in this company.
Definitions for metabolic syndromeWe obtained health checkup data including age, waist circumference, body weight, height, systolic blood pressure (SBP), diastolic blood pressure (DBP), fasting glucose (FG), hemoglobin A1c (HbA1c), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), and the use of antihypertensive drugs, diabetes, and dyslipidemia. Body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared. Metabolic syndrome was defined as central obesity and the presence of two or more of the following symptoms: hypertension, glucose intolerance, and dyslipidemia, according to the Japanese Committee for Diagnostic Criteria10). Central obesity was defined as waist circumference ≥85 cm in men. Hypertension was defined as SBP ≥130 mmHg, DBP ≥85 mmHg, or the use of antihypertensive drugs. Glucose intolerance was defined as FG ≥110 mg/dL or the use of drugs for diabetes. For workers without fasting glucose data, glucose intolerance was defined as HbA1c ≥6.0% or the use of drugs for diabetes11). Either fasting glucose or HbA1c was measured in the workers. Specifically, fasting glucose was measured in the workers who had not eaten breakfast on health checkup day, and HbA1c was measured in the other workers. Dyslipidemia was defined as TG ≥150 mg/dL, HDL-C <40 mg/dL, or the use of antihyperlipidemic drugs.
Definitions for migrant workerWe conducted a self-administered questionnaire survey in August 2017. In the questionnaire, domestic migration was assessed by asking “Did you change where you live for the purpose of engaging in decontamination work (including dormitories and hotels)?” with two response options (Yes and No). The workers who answered “Yes” to the question were defined as domestic migrant workers, and the others as non-migrant workers.
Statistical analysisData were analyzed using SPSS ver. 23 (SPSS Inc., Chicago, IL, USA). Mean and standard deviation (SD) were calculated for age, BMI, waist circumference, SBP, DBP, FG, and HbA1c, after confirming a resemblance to a normal distribution on histograms. Median and the 25th–75th percentiles were calculated for TG and HDL-C. The prevalence of metabolic syndrome and its components were calculated using frequencies and proportions. To assess the relationships between domestic migration and each item, we conducted the Student t-test, Welch’s t-test, or Mann-Whitney U test for continuous variables and chi-square test for categorical variables. To estimate the odds ratio (OR), along with the 95% confidence interval (CI) for the presence of metabolic syndrome and its components across the migrants, we used logistic regression analysis. Additionally, we adjusted for age as a continuous variable in the basic model. The p-value was two-sided; a p-value below 0.05 was regarded as statistically significant.
EthicsThis study was approved by the Ethics Committees of Fukushima Medical University (Application No. 29048). We obtained written informed consent from each worker.
The descriptive statistics are shown in Table 1. Of the 91 workers, 32 (35.1%) were domestic migrant workers. The mean age of the workers was 49.5 (SD, 13.8) years. For glucose intolerance, 66 workers did not have fasting glucose data and used HbA1c data. The prevalence of metabolic syndrome, central obesity, hypertension, glucose intolerance, and dyslipidemia were 19.8%, 41.8%, 54.9%, 29.7%, and 34.1%, respectively. Table 2 shows the ORs of metabolic syndrome and its parameters. The age-adjusted odds ratios of domestic migrant workers for metabolic syndrome, central obesity, hypertension, glucose intolerance, and dyslipidemia were 1.75 (95% CI, 0.60–5.10), 2.45 (95% CI, 1.01–5.94), 1.07 (95% CI, 0.39–2.94), 0.40 (95% CI, 0.13–1.25), and 0.87 (95% CI, 0.34–2.20), respectively, compared to non-migrant workers.
| Mean±SD, Median (25th–75th percentiles), or % | Total workers (N=91) | Migrant workers (N=32) | Non-migrant workers (N=59) | p-value |
|---|---|---|---|---|
| Age (years) | 49.5±13.8 | 48.0±14.9 | 50.3±13.3 | 0.448*1 |
| BMI (kg/m2) | 24.4±3.5 | 25.2±3.7 | 24.0±3.4 | 0.141*1 |
| Waist circumference (cm) | 84.2±9.2 | 86.3±10.3 | 83.1±8.4 | 0.118*1 |
| Systolic blood pressure (mmHg) | 126.8±15.2 | 127.3±14.8 | 126.5±15.5 | 0.800*1 |
| Diastolic blood pressure (mmHg) | 76.3±10.5 | 78.2±10.5 | 75.2±10.4 | 0.199*1 |
| Fasting glucose (mg/dL) | 100.8±23.9 | 103.1±27.3 | 98.0±19.7 | 0.609*1 |
| (N=25) | (N=14) | (N=11) | ||
| HbA1c (%) | 6.2±1.5 | 5.7±0.6 | 6.3±1.7 | 0.029*2 |
| (N=66) | (N=18) | (N=48) | ||
| Triglyceride (mg/dL) | 106.0 | 114.0 | 98.0 | 0.768*3 |
| (75.0–155.0) | (75.0–171.25) | (75.0–152.0) | ||
| HDL-cholesterol (mg/dL) | 56.0 | 53.5 | 58.0 | 0.314*3 |
| (47.0–68.0) | (44.0–62.75) | (49.0–69.0) | ||
| Metabolic syndrome | 18 (19.8) | 8 (25.0) | 10 (16.9) | 0.357*4 |
| Central obesity | 38 (41.8) | 18 (56.3) | 20 (33.9) | 0.039*4 |
| Hypertension | 50 (54.9) | 17 (53.1) | 33 (55.9) | 0.797*4 |
| Glucose intolerance | 27 (29.7) | 6 (18.8) | 21 (35.6) | 0.093*4 |
| Dyslipidemia | 31 (34.1) | 10 (31.3) | 21 (35.6) | 0.676*4 |
BMI, body mass index; HbA1c, glycated hemoglobin; HDL, high-density lipoprotein; SD, standard deviation.
| Metabolic syndrome | Central obesity | Hypertension | Glucose intolerance | Dyslipidemia | ||
|---|---|---|---|---|---|---|
| Unadjusted OR (95% CI) | Non-migrant | 1 (reference) | 1 (reference) | 1 (reference) | 1 (reference) | 1 (reference) |
| Migrant | 1.63 | 2.51 | 0.89 | 0.42 | 0.82 | |
| (0.57–4.67) | (1.04–6.06) | (0.38–2.12) | (0.15–1.18) | (0.33–2.06) | ||
| Age-adjusted*1 OR (95% CI) | Non-migrant | 1 (reference) | 1 (reference) | 1 (reference) | 1 (reference) | 1 (reference) |
| Migrant | 1.75 | 2.45 | 1.07 | 0.40 | 0.87 | |
| (0.60–5.10) | (1.01–5.94) | (0.39–2.94) | (0.13–1.25) | (0.34–2.20) |
CI, confidence interval; OR, odds ratio.
In this study, we investigated the association between metabolic syndrome or its components and domestic migration in the radiation decontamination workers. Despite no significant difference in the prevalence of metabolic syndrome between domestic migrant and non-migrant workers, central obesity was more prevalent in domestic migrant workers, which reflected excessive visceral fat as the basis of metabolic syndrome. These findings may call attention to metabolic syndrome and central obesity among domestic migrant workers.
A previous study by Bi et al. demonstrated the association between the prevalence of central obesity and migrant workers compared to the general population6). However, as the prevalence of metabolic syndrome and lifestyle habits are different in each occupation category7,8), further analyses would be required to determine whether the prevalence was attributable to domestic migration or occupation. We therefore employed subjects engaged in the same occupation and compared the prevalence of central obesity between domestic migrant and non-migrant workers. Our findings showed the significant association with domestic migrant workers and central obesity. In Japan, many domestic migrant workers live alone separated from their family and this working style is called Tanshin funin. Domestic migrant workers can be considered to be a type of Tanshin funin workers. Generally, the lifestyle habits of Tanshin funin workers, such as dietary and exercise habits, are poor12). Moreover, about 30% of radiation decontamination workers lived in company dormitories and hotels, which were shared accommodation13), and migrant workers had anxieties regarding their personal time14). Their residential status may lead to poor lifestyle habits and a high prevalence of central obesity. Central obesity is a root of metabolic syndrome5) and could potentially cause metabolic syndrome in the future. Effective primary intervention is needed in this population.
Despite the high prevalence of central obesity in the domestic migrant workers, the prevalence of glucose intolerance and dyslipidemia tended to be higher in the non-migrant workers. This conflicting result was similar to a previous study6), which is probably because of two reasons. First, domestic migrant workers are type of self-selected individuals15). Unhealthy individuals who were under medication had a high probability to stay in their hometown and not migrate for work. Second, in this study, some non-migrant workers had lived in Iitate village, and left their hometown after the evacuation. Previous studies have shown that evacuation was associated with the incidence of diabetes16) and dyslipidemia17). The evacuation of non-migrant workers may reduce the difference in health status between domestic migrant and non-migrant decontamination workers.
There were some limitations to our study. First, it was arbitrary for the workers to receive either the HbA1c or FBS test as an index of glucose tolerance. Further examination is needed with a unified standard for a glucose tolerance test. Second, we were unable to receive health status data before domestic migration and examine changes over time. Third, all subjects worked in a single location, Iitate village. Thus, further investigation including decontamination workers working in multiple locations are necessary. Fourth, we were unable to examine the workers’ lifestyle habits. Further investigation into the effect of lifestyle habit on the relationship between migration and metabolic syndrome is needed. Fifth, the external validation for workers with other occupation was unclear. Additional research of workers with other occupation is further study. Despite these limitations, this study was the first to focus on domestic migrant workers and metabolic syndrome in one occupational category. Our findings should support public-health policy makers to give sufficient resources to domestic migrant workers. We think that the knowledge of this study will not only apply to these workers. When employment expands rapidly, such as that in disaster reconstruction or other big events, a large number of workers might migrate for work. The result of this study should adapt these situations.
In conclusion, we revealed that the domestic migrant radiation decontamination workers had a high prevalence of central obesity compared with non-migrant workers, despite no significant difference of the prevalence of metabolic syndrome. Efforts to avoid the development from central obesity to metabolic syndrome is essential to this population. Further longitudinal investigation is necessary for health promotion in domestic migrant workers.
Shota Endo and Takeyasu Kakamu are occupational health physicians of the research subject company.
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