Smoking increased the risk of developing amyotrophic lateral sclerosis by 12 percent

A systematic review and meta-analysis by South Korean scientists found that smoking increased the risk of developing amyotrophic lateral sclerosis (ALS) by 12 percent. The association was most pronounced in a subgroup of current smokers, who had a 28 percent increased risk of developing the disease. The analysis is published in the journal Tobacco Induced Diseases.

ALS affects the structures of the nervous system responsible for movement - the motor cortex or anterior horns of the spinal cord and cranial nerve nuclei. It is manifested by a progressive decline in muscle strength and spasticity. Because of the lack of effective treatments and its increasing prevalence, ALS is considered a global public health problem.

Physicians know that a variety of risk factors, both genetic and environmental factors, influence the development of ALS. Exposure to mercury, lead, pesticides, solvents, head trauma, electrical shock and lower body mass index have been suggested as potential risk factors for development. However, in recent years, an increasing role in the development of ALS has been attributed to smoking, and the effect size has been estimated differently.

Therefore, Yun Hak Kim and colleagues at Busan National University conducted a systematic review and meta-analysis of 32 studies (28 case-control studies and four cohort studies) conducted between 1981 and 2022 in the United States, Europe, Japan, and China. The primary unadjusted analysis showed that smoking increased the overall risk of developing ALS by 14 percent. After statistical adjustment of the results, this risk was 12 percent (p = 0.009). This analysis calculated the overall risk in the entire sample: both people who had ever smoked (including those who had quit) and people who were current smokers.

In addition, people who continued to smoke had a 28 percent increased risk of developing ALS (in both adjusted and unadjusted analyses, p = 0.001). When subgroup analyses were analyzed by sex, it was found that smoking increased the risk of ALS by 25 percent in women and one percent in men. However, when comparing the two subgroups, this difference was found to be statistically insignificant. Notably, plots of the dose-effect relationship (number of pack-years and risk of developing the disease) showed an inverted U-shaped curve.

This meta-analysis showed a statistically significant increase in the risk of developing ALS with smoking. People who continued to smoke were at the highest risk. Although scientists have yet to explain the inverted U-shaped relationship between pack-years and risk of developing the disease, the data already support the danger of smoking in relation to the risk of developing ALS.