While smoking is a pervasive risk factor for many diseases, its connection to amyotrophic lateral sclerosis (ALS) has been unclear. Researchers from Pusan National University addressed this gap by conducting a comprehensive study investigating the association between ALS and smoking. They also explored how biological sex and smoking status affect this association. Their results highlight how eliminating modifiable risk factors can help mitigate the risk of developing ALS.

Amyotrophic lateral sclerosis (ALS), a neurodegenerative disorder, is a significant global health issue, affecting the voluntary motor nervous system in affected individuals. It is further compounded by a lack of effective treatment options. This treatment gap highlights the need to identify risk factors, particularly modifiable ones, that could potentially prevent the onset of ALS. 

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While smoking has been considered a significant risk, studies have yielded inconclusive results, failing to pinpoint the exact association. Investigating this link is crucial to understand preventive strategies and advancing our understanding of ALS etiology.

To shed light on this association, a team of researchers from South Korea, led by Assistant Professor Yun Hak Kim, MD, PhD, from the Department of Anatomy and the Department of Biomedical Informatics at Pusan National University, conducted a meticulous study.

Employing a systematic literature search within the patients/population, intervention, control, and outcomes or PICO framework, they identified case-control and cohort studies delving into the relationship between smoking and the onset of ALS. The team determined the dose-response relationship between smoking and ALS by analyzing the number of packs smoked per year by patients.

In their study, the findings of which were published in Volume 22, Issue 13 of the journal Tobacco Induced Diseases on 18 January 2024, the in-depth analysis of 32 studies revealed a notable association between smoking and an increased risk of ALS. The research team analyzed the adjusted odds ratios (OR) to provide a quantitative measure of the association between smoking and ALS.

The adjusted odds ratio calculations showed that smokers are 1.12 times more likely to exhibit a risk of developing ALS. Further analysis showed that this association is stronger for current smokers.

“One of our most pivotal findings was the dose-response analysis, revealing an inverted U-shaped curve,” says Dr Kim. “This curve highlights that the risk associated with smoking isn’t a linear progression. Instead, it peaks and then starts to decrease or plateau, suggesting that the risk of ALS is influenced by the intensity of smoking.” The non-linear nature of the curve challenges conventional beliefs and highlights the need for personalized public health interventions tailored to specific smoking behaviors.

The study also unveiled a noteworthy association between smoking and the risk of ALS, predominantly among women compared to men. Dr Kim observes, “In our investigation, the unadjusted OR stood at 1.20, signifying a substantial correlation between smoking and ALS among females. The adjusted OR remained significant at 1.25, reinforcing the elevated risk for ALS among female smokers. In contrast, no significant link was observed in males, potentially due to occupational exposures overshadowing the impact of smoking.”

These findings not only provide valuable insights into the risk profile for women but also emphasize the significance of public health programs aimed at mitigating the impact of smoking on ALS within this specific demographic.

In summary, this study provides compelling evidence of a positive relationship between smoking and the risk of ALS. Identifying smoking as a modifiable risk factor highlights the potential for mitigating the risk of developing ALS through smoking cessation. Encouraging individuals to discontinue smoking is crucial, given its tangible impact on reducing the likelihood of ALS onset.

Featured image: Infographic showing link between smoking and ALS risk. Image: Pusan University, South Korea