Regional disparities in Japan's progress towards the Health Japan 21 smoking reduction target.

Background: Japan's 'Health Japan 21' initiative targets a reduction in adult smoking prevalence to 12% by 2032. This study evaluates the probability of meeting this target at both national and prefectural levels by estimating and comparing prevalence trends.

Method: Using crude smoking prevalence data from 2001 to 2022 for the whole nation and across Japan's 47 prefectures, we used Bayesian linear regression to project future smoking trends up to 2100. We calculated the posterior probabilities of each prefecture achieving the target by 2032 and projected the timeline for meeting this target. We defined 'meeting the target' as having a 60% or higher probability.

Results: Nationally, 2022 smoking prevalence was 16.09%, accompanied by an annual reduction rate of 3.75%. There is a 64.3% probability of achieving the 12% smoking prevalence target by 2032, with considerable prefectural variation. Out of 47 prefectures, 19 are on track to meet the target by 2032, whereas 28 are predicted to lag this deadline. For example, Tokyo (99.3% probability) and Nara (98.0% probability) could potentially reach this target as early as 2026 whereas Fukushima, Iwate and Aomori have <1% probability of achieving the target by 2032 and are not projected to reach the target until 2046 or later.

Conclusions: While Japan may achieve its national smoking reduction target by 2032, there are large regional variations. This variability underscores the need for tailored public health strategies that address the unique challenges faced by each prefecture to ensure a cohesive and effective tobacco control approach across the nation.