Thyroid Cancer and Precancerous Morbidity After Nuclear Fallout: Long-Term Cohort Study Near the Semipalatinsk Test Site.

BACKGROUND

Populations living near the Semipalatinsk Nuclear Test Site (SNTS) in Kazakhstan were chronically exposed to low-to-moderate doses of ionizing radiation due to atmospheric nuclear testing (1949-1962). While the effects of acute exposures are well documented, data on long-term endocrine outcomes in chronically exposed adults remain limited.

OBJECTIVE

To evaluate thyroid and metabolic morbidity and its association with reconstructed radiation dose in a long-term adult cohort exposed to fallout.

METHODS

This cohort study included 3,240 individuals who underwent thyroid ultrasound screening between 1998 and 2002. Thyroid doses were reconstructed individually using a fallout-specific dosimetric model based on age, diet, and geographic location across 125 nuclear tests. Endocrine outcomes were assessed through ICD-10 diagnoses and follow-up surveys in 2023-2024. Associations between dose and endocrine morbidity were analyzed using logistic regression, adjusted for sex, age at exposure, smoking, obesity, parity, and hormone therapy.

RESULTS

By 2024, 1,099 individuals (33.9%) were alive. Among them, 63% reported thyroid disease, 33% had received hormone therapy, and 2% had undergone surgery. Verified endocrine diagnoses were identified in 712 individuals (21.9%), including non-toxic diffuse goiter (28.1%), multinodular goiter (19.5%), and single nodular goiter (7.9%). Thyroid dose was positively associated with endocrine morbidity (OR = 1.42; 95% CI: 1.22-1.65; p < 0.001). Female sex, early exposure, obesity, and smoking were also significant predictors.

CONCLUSIONS

Decades after fallout exposure, thyroid and metabolic disorders remain prevalent in affected populations. The findings support continued endocrine surveillance and provide robust evidence of a dose-dependent endocrine risk in adults exposed to environmental radiation.