The risk of developing ALS increases 44% for former smokers and 42% for current smokers, compared with individuals who have never smoked
Smoking has been identified as a probable risk factor for amyotrophic lateral sclerosis (ALS), with age at initiation the most predictive factor for the disease, according to the results of a study published in the February issue of Archives of Neurology.
Hao Wang, MD, PhD, from the Harvard School of Public Health in Boston, and colleagues analyzed data from five long-term studies about lifestyle factors and risks for chronic disease. Participants in Dr. Wang’s study were enrolled in the Nurses’ Health Study, the Health Professionals Follow-up Study, the Cancer Prevention Study II Nutrition Cohort, the Multiethnic Cohort, and the NIH–AARP Diet and Health Study. Follow-up ranged from nine to 18 years, and age at baseline ranged from 29 to 93.
More than 1.1 million participants were included in the study (562,804 men and 556,276 women), and 832 cases of ALS were documented. Smokers and nonsmokers in all five cohorts were similar in terms of BMI, physical activity, and education, but the investigators found that the rates of ALS increased with age and were consistently higher in men than women for each age group.
“The relative risk increased by 10% for each increment of 10 cigarettes smoked per day and by 9% for each 10 years of smoking,” Dr. Wang’s group reported. “Significant trends in the risk of ALS were observed with the duration of smoking and the number of cigarettes smoked per day, but these trends were largely driven by the low ALS risk among never smokers.“
Age at Initiation Was the Strongest Predictor of ALS Risk
To account for the effect of never smokers on the data, the investigators also analyzed a cohort of smokers only. “The only aspect of smoking behavior that remained predictive of ALS risk was age at smoking initiation; a younger age was associated with a higher risk of ALS,” the researchers commented, with an increased risk for each five years younger at initiation.
“There are few established risk factors for ALS,” Dr. Wang’s group wrote. There are also several possible mechanisms through which cigarette smoking can influence ALS risk. “Better understanding of the relation between smoking and ALS may further the discovery of other risk factors and help elucidate the nature of the disease,” the authors concluded.
—Ariel Jones