A large U.S. study suggests that the age and type of groundwater supplying drinking water may be linked to Parkinson’s disease risk.
A new preliminary study suggests that the age of the groundwater supplying a community’s drinking water may be linked to the risk of Parkinson’s disease. The research will soon be presented at the American Academy of Neurology’s 78th Annual Meeting. The findings show an association but do not prove that newer groundwater causes Parkinson’s disease.
The researchers focused on two main factors: how old the groundwater was and the type of aquifer it came from. An aquifer is an underground layer of porous rock, silt, or sand that stores and carries water below the surface.
“One way to examine our exposure to modern pollution is through our drinking water,” said study author Brittany Krzyzanowski, PhD, of Atria Research Institute in New York City, who conducted this research while at Barrow Neurological Institute in Phoenix, Arizona, and is a member of the American Academy of Neurology. “Newer groundwater, created by precipitation that has fallen within the past 70 to 75 years, has been exposed to more pollutants. Older groundwater typically contains fewer contaminants because it is generally deeper and better shielded from surface contaminants. Our study found that groundwater age and location is a potential environmental risk factor of Parkinson’s disease.”
Study Population and Data Sources
The study included 12,370 people diagnosed with Parkinson’s disease and more than 1.2 million people without the condition. Participants were matched based on age, sex, and race and ethnicity. All lived within three miles (about 4.8 kilometers) of 1,279 groundwater sampling sites located across 21 major aquifers in the United States.
The research team analyzed groundwater age, aquifer category, and drinking water source, including municipal groundwater systems and private wells. These factors were used as indicators of possible exposure to neurotoxic contaminants.
Carbonate aquifers are the most widespread type in the United States. They are largely made of limestone, and water moves through cracks and channels in the rock. Because water can travel quickly through these openings, carbonate aquifers may be more susceptible to contamination from the surface.
Glacial aquifers formed more than 12,000 years ago as glaciers advanced and retreated. They consist mainly of sand and gravel, with water stored in the spaces between particles. In these systems, water tends to move more slowly and is filtered more naturally as it passes underground.
In the United States, carbonate aquifers are common in parts of the Midwest, the South, and Florida. Glacial aquifers are found primarily in the Upper Midwest and the Northeast.
Differences in Parkinson’s Risk by Aquifer Type
Among participants with Parkinson’s disease, 3,463 received their drinking water from carbonate aquifers, 515 from glacial aquifers, and 8,392 from other types of aquifers. Among those without Parkinson’s disease, 300,264 used water from carbonate aquifers, 62,917 from glacial aquifers, and 860,993 from other aquifers.
After accounting for age, sex, income, and air pollution, the researchers found that people whose water came from municipal systems or private wells drawing from carbonate aquifers had a 24% higher risk of developing Parkinson’s disease compared with those whose water came from other aquifer types. When compared specifically with people using water from glacial aquifers, the risk was 62% higher.
The apparent protective link with older groundwater was observed only in carbonate aquifers. For each one standard deviation increase in groundwater age, the risk of Parkinson’s disease decreased by about 6.5%. In addition, groundwater that entered the system within the past 75 years in carbonate aquifers was associated with an 11% higher risk of Parkinson’s disease compared with groundwater that has been underground for more than 12,000 years, dating back to the last ice age.
“We speculate that the apparent protective effect of older groundwater is seen mainly in carbonate aquifers because these systems can show a clearer contrast between newer and older water,” said Krzyzanowski. “In these aquifers, newly recharged groundwater is more vulnerable to surface contamination, while older groundwater can remain cleaner if it is separated from recent inputs by a confining layer.”
“In contrast, glacial aquifers tend to slow groundwater movement and naturally filter contaminants as water travels underground,” said Krzyzanowski. “As a result, differences in contamination between newer and older groundwater in these aquifers may be smaller and therefore harder to detect.”
Public Health Implications and Study Limitations
Krzyzanowski said that people can often learn about the source of their drinking water by contacting their local water utility. Those who rely on private wells may be able to obtain information from state or county groundwater agencies.
“This study highlights that where our water comes from, including the age of groundwater and the type of water source, could shape long-term neurological health,” said Krzyzanowski. “While additional research is needed, bringing together knowledge about groundwater and brain health may help communities better assess and reduce environmental risks.”
One limitation of the study is that researchers assumed everyone living within a three-mile (about 4.8 kilometer) radius of a sampling site was exposed to the same aquifer characteristics and groundwater age as the sampled location. Individual differences in water sources or exposure were not directly measured.
Meeting: American Academy of Neurology’s 78th Annual Meeting
The study was supported by AAN Clinical Research Training Scholarship, American Brain Foundation, and The Parkinson’s Foundation.
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