A preliminary study by U.S. Department of Agriculture (USDA) researchers and colleagues suggests that in some parts of South Carolina, the risk of stroke may be linked in part to regional soil characteristics. These findings could provide new leads for investigating factors associated with the incidence of stroke.

The research was conducted by Medical University of South Carolina professor Daniel Lackland and Agricultural Research Service (ARS) research leader Patrick Hunt, microbiologist Thomas Ducey, and soil scientist Jarrod Miller. The ARS team works at the agency's Coastal Plains Soil, Water and Plant Research Center in Florence, S.C. Retired ARS soil scientist Warren Busscher, who worked at the Florence laboratory, also contributed to the project. ARS is USDA's chief intramural scientific research agency.

To identify associations between stroke risk and soil characteristics, the scientists compared 10 years of South Carolina inpatient and emergency room discharge data to information in a state soil database. They found significant correlations between stroke rates, soil depth to water, and soil drainage class.

The team then focused their investigation on soil characteristics in South Carolina counties with the 10 highest stroke rates—all within the Coastal Plain—and counties with the 10 lowest stroke rates, all in the Blue Ridge/Piedmont region. Their results indicated that soils with a depth to water table from 20 to 59 inches were correlated with geographic population stroke mortality rates, as were moderately well-drained to poorly-drained soils and strongly acidic soils. They also observed that well-drained soils and soils with a depth to water table below 79 inches had a negative correlation.

The moderately well-drained to poorly-drained soils and strongly acidic soil characteristics in the areas of high stroke mortality rates are typically found in Coastal Plain soils. If this correlation of soil characteristics and stroke risks is real, the scientists believe the biological correlates might include the prevalence—or perhaps lack—of specific microbes in the region's moist, acidic soils, which can be very different from organisms that live in drier, more basic soils.

How these soil microbes could specifically affect human health is unknown. But soil biogeochemical characteristics may provide additional information to the lifestyle, environmental and genetic factors in explaining the enigma of the Southeastern "stroke belt."

Findings from this research were published in 2012 in The Journal of Environmental Science and Health.