Objectives Emerging evidence suggests that low-dose ionizing radiation increases the risk of neurodegenerative diseases. Past studies have relied on death data to identify dementia, and these are prone to under-ascertainment and complicate the estimation of health risks as individuals tend to live with dementia for many years following onset. We present findings from the first occupational cohort to investigate dementia risk from low-dose radiation using incident outcomes.

Methods This is a retrospective cohort of 60 874 Ontario Nuclear Power Plant workers from the Canadian National Dose Registry. Personal identifiers were linked to Ontario population-based administrative health data. Incident dementias between 1996 and 2022 were identified using a validated algorithm based on physician, hospital, and prescription drug data. Individual-level annual estimates of whole-body external ionizing radiation were derived from personal workplace monitoring. The incidence of dementia among these workers was compared to a random sample of Ontario residents matched by sex, age, and residential area. Internal cohort analysis using Poisson and linear excess relative risk (ERR) models, adjusted for sex, attained age, calendar period, and neighborhood income quintile, were used to characterize the shape of the exposure-response curve between low-dose cumulative radiation (lagged 10 years) and incident dementia.

Results There were 476 incident dementias and 867 028 person-years of follow-up. The mean whole-body lifetime accumulated exposure at the end of follow-up was 11.7 millisieverts (mSv). Workers with cumulative exposure between 50–100 mSv had an increased risk of dementia [RR 1.50, 95% confidence interval (CI) 0.99–2.28] compared to those unexposed. Spline analysis suggested that the dose–response relationship was non-linear. The linear ERR per 100 mSv increase in exposure was 0.704 (95% CI 0.018–1.390).

Conclusion Our findings suggest that low-dose exposure to ionizing radiation increases the risk of incident dementia.

Key terms Canada; dementia; dementia incidence; exposure; ionizing radiation; nuclear power; occupational health; Ontario; power plant worker; radiation risk

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