Living near green space may reduce risk of developing ALS

Living in areas with a moderate amount of green space appears to reduce the likelihood of developing amyotrophic lateral sclerosis (ALS) — but both very low and very high levels of greenness may increase the odds for different reasons, according to a study from Italy.

The findings “may have public health implications including disease prevention and urban planning,” the researchers wrote. Their study, “Green space exposure and risk of amyotrophic lateral sclerosis: a population-based case-control study in Northern Italy,” was published in Environmental Health.

ALS is a neurodegenerative disease that damages motor neurons, the nerve cells that control voluntary movement. The causes of ALS are not yet fully understood, but both genetic and environmental factors may play a role. One environmental factor receiving attention is greenness, or the amount of vegetation and green spaces around where people live.

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To better understand the link between greenness and ALS, the researchers conducted a study across the provinces of Modena, Reggio Emilia, and Parma in northern Italy. The study included 499 patients newly diagnosed with ALS from 1998 to 2011 and 1,935 healthy adults matched by sex, age, and province of residence.

The average age at which ALS began was 67.2. There were more men than women (53.9% vs. 46.1%) and, on average, men developed the disease 4.7 years earlier than women (65.1 vs. 69.8). Of the 499 patients, 235 were from Modena, 152 from Reggio Emilia, and 112 from Parma.

The researchers measured greenness near each person’s home using six environmental indicators based on satellite images and land-use data. One key measure was the Normalized Difference Vegetation Index (NDVI), which estimates the amount of healthy vegetation present. They also used measures of green cover, accessibility to green areas, and a combined measure called the Green Exposure Index (GEI).

The study found a U-shaped relationship between greenness and the risk of developing ALS, meaning that both very low and very high levels of greenness were associated with higher odds of developing the condition than moderate levels. The pattern was strongest when using NDVI-based measures.

Areas with low greenness, especially in urban environments, often had low NDVI values. In these areas, people have less access to parks and natural spaces, potentially reducing their time spent in physical activity and increasing their exposure to outdoor air pollution. Surprisingly, very green areas were also associated with a higher risk of ALS. The researchers suggested this could be related to greater exposure to pesticides.

The researchers adjusted their analyses for other possible environmental factors, including magnetic fields and exposure to artificial nighttime lighting. After these adjustments, the findings remained largely unchanged, suggesting the link between greenness and ALS was relatively stable.

When men and women were analyzed separately, the overall pattern remained similar. However, women showed a clearer U-shaped pattern for some GEI measures, with the lowest odds at moderate levels of greenness and higher odds at both extremes. While there may have been inaccuracies in estimating exposure based solely on home address, the findings suggest that moderate access to green spaces may be associated with lower ALS risk.

“These findings highlight the need to consider the environmental context underlying green spaces, particularly in relation to urban, agricultural and rural exposures,” the researchers wrote. “Future studies integrating detailed data on pesticide use, air pollution, land-use practices, and individual mobility patterns will be essential to better define the relation between greenness and ALS.”