Exposure to pesticides sprayed on fruits, vegetables and other plants could raise the risk of Amyotrophic Lateral Sclerosis, or ALS, by up to 70 percent, according to a new study. People who work directly with the chemicals, such as farmers, face a dramatically higher chance of developing the disease.
ALS, also known as Lou Gehrig's disease, affects around 35,000 Americans. It causes the nerve cells that control movement to deteriorate, leading to muscle weakness, loss of mobility, speech difficulties and changes to thinking and behavior. Just 20 percent of ALS patients live longer than five years, and in many cases the prognosis is as little as two years.
The cause of the disorder is not fully known, but scientists from the Robert Sauvé Institute For Research in Quebec identified a possible link. The team reviewed almost 800 studies but used 11 for their analysis, drawing on data from more than 2,000 people with ALS.
The researchers found that people exposed to pesticides at work were around 60 percent more likely to develop ALS than those never exposed. Those exposed mostly to herbicides, or weedkiller, had a 70 percent increased risk. Pesticides are chemicals used to protect crops by killing or controlling weeds, insects and fungi, and the main types are herbicides, insecticides and fungicides.
Even lower levels of exposure to pesticides of any kind were linked to roughly double the risk, the study found. When researchers analyzed men and women separately, they found the link only applied to men.
Researchers call for workplace changes
Writing in the journal Occupational and Environmental Medicine, the study's authors urged officials to introduce interventions aimed at reducing exposure during occupational pesticide use. The World Health Organisation has branded pesticides "intrinsically toxic" and named them among the leading causes of death by self-poisoning. Many pesticides banned in other countries remain permitted for use in the United States.
Among the chemicals still legal in the US is paraquat, a weedkiller outlawed across Europe and in more than 70 countries, which dozens of studies have linked to Parkinson's disease. Vermont became the first state to move to ban its use this year. Chlordane, a pesticide used to kill termites, has been linked to ALS in separate studies and was banned in the US in 1988 over health fears.
High-profile ALS cases draw attention
The study comes amid high-profile cases of ALS diagnosed in the US. NFL legend Chris Johnson revealed his diagnosis at age 40 last month in an interview in which he communicated only through an eye-controlled computer. Eric Dane, known for playing Dr. Mark Sloan on Grey's Anatomy, died from ALS earlier this year at age 53, two years after his diagnosis.
The illness can strike seemingly healthy adults in the prime of their lives. Inherited genetic mutations account for around one in ten cases, but the cause of the vast majority remains a mystery, and researchers have increasingly pointed to environmental factors such as pesticide exposure, pollution and diet.
Outside experts urge caution
Dr. Johnathan Cooper-Knock, a clinical lecturer at the University of Sheffield's School of Medicine and Population Health who was not involved in the study, said the strength of the research lies in its use of data from eleven different studies and more than 2,000 ALS patients, calling the findings interesting and worthy of further work. He cautioned, however, that the analysis is retrospective and uses indirect measurements of pesticide exposure, making it almost impossible to know whether the effect seen is caused by pesticide exposure or some unseen factor that may be correlated with it.
