Cigarette Smoking Linked to Increased Risk of Amyotrophic Lateral Sclerosis
Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, is a neurodegenerative disorder affecting more than 5,500 each year in the United States. It is estimated that about 90% of ALS cases are sporadic and of unknown origins, which leads researchers to believe a cause might be environmental. Cigarette smoking is one of those environmental factors that can increase risk.
The More One Smokes, the Greater the Risk of ALS
In amyotrophic lateral sclerosis, nerve cells waste away or die and can no longer send messages to the muscles, leading to muscle weakening, twitching, and an inability to move the arms, legs, and body. Symptoms usually do not develop until after age 50 but the disease can start in younger people. Eventually, breathing or swallowing is affected, leading to death, usually within 3 to 5 years of diagnosis.
Hao Wang MD PhD, of the Harvard School of Public Health, and colleagues analyzed data from five different long-term studies involving a total of more than 1.1 million participants. Just over 800 of those had ALS.
Overall, the rate of ALS increased with age was higher in men than in women for all age groups.
The researchers found that those who had smoked cigarettes at any point in their lives had an increased risk of developing ALS over those who had never smoked. Current smokers had a 42% increased risk and former smokers had a 44% increased risk.
The more one smoked, the greater the risk. For each increment of 10 cigarettes smoked per day, the risk of developing ALS increased 10%. Additionally, for each 10 years of smoking, the risk increased by 9%. Those who started smoking earlier in life had an increased risk over those who took up the habit later.
The authors suggest several possible mechanisms by which cigarette smoking influences ALS risk. These include direct neuronal damage from the components of cigarette smoke, especially nitric oxide or residues from pesticides used in tobacco cultivation. In 2008, exposure to formaldehyde, a by-product from the combustion of tobacco smoke, was reported to be associated with increasing the risk of ALS.
Oxidative stress may also be a factor. In 1993, scientists from the National Institute of Neurological Disorders and Stroke (NINDS) found that a mutation in a gene that produces the SOD1 enzyme – a powerful antioxidant that protects the body from free radicals – was associated with some cases of familial ALS.
“Chemicals that are present in cigarette smoke generate free radicals and products of lipid peroxydation, and smokers have a higher turnover of the major antioxidant vitamin C,” write the authors who published their work in the Archives of Neurology.
Arch Neurol. 2011;68:207-214