'Greenness' Tied to Lower Hospitalization Risk for Neurodegenerative Diseases

Greater exposure to natural environments was associated with a lower risk of hospitalization for neurodegenerative diseases in a cohort of older individuals.

Among Medicare beneficiaries, increasing amounts of greenness and park cover correlated with decreasing hospitalization risk for Parkinson's disease:

• Greenness: HR 0.94 per interquartile range (IQR) increase (95% CI 0.93-0.95)
• Park cover: HR 0.97 per IQR increase (95% CI 0.97-0.98)

And the risk for Parkinson's disease hospitalization was lower for beneficiaries living in areas with at least 1% of surface water (HR 0.97, 95% CI 0.96-0.98), according to researchers led by Jochem O. Klompmaker, PhD, of the Harvard T.H. Chan School of Public Health in Boston.

In addition, greenness -- defined as significant presence of living vegetation -- was associated with a decreased hospitalization risk for Alzheimer's disease and other related dementias (ADRD; HR 0.95 per IQR increase, 95% CI 0.94-0.96), they detailed in JAMA Network Open.

"We observed protective associations," Klompmaker told MedPage Today. "These hazard ratios may look small, but they can translate into large numbers of cases that could be prevented when interventions are taken."

Increased green spaces, parks, and blue space could have an impact, he said.

The researchers also noted that the association between decreased hospitalization risk for Parkinson's disease and park cover was greatest in zip codes with low socioeconomic status.

"It shows that parks are especially important for them," said Klompmaker. "We don't know the exact reason for that, but I think especially for urban planners and policymakers, that's something important to see."

He pointed out that his team's analysis was necessarily very broadly defined. They used satellite images to determine greenness, known as the normalized difference vegetation index, and zip code-level data about parks and blue spaces, but they did not have data on how people interacted with these spaces on a daily basis. He also said that greenness could apply to inaccessible places for most people, such as farmland or highway medians.

Still, the main takeaway from this research was that it affects everyone to some degree because these spaces exist in every neighborhood, Klompmaker added, noting that other studies have shown greenness to be negatively associated with cardiovascular disease hospitalization.

"It's important to understand that the environment that we live in affects our health in multiple ways," he said. "I think that's something we should recognize more often."

In this study, 61,662,472 Medicare fee-for-service beneficiaries age 65 and up made up the ADRD cohort, and 61,673,367 beneficiaries made up the Parkinson's cohort. All beneficiaries lived in the contiguous U.S. from January 2000 through December 2016.

Among both cohorts, 55.2% of beneficiaries were women, 84.4% were white, 76.6% were ages 65 to 74 at study entry, and 87.6% were not eligible for Medicaid.

Among their cohorts, Klompmaker and team observed 7,737,609 ADRD and 1,168,940 Parkinson's disease hospitalizations.

Greenness and park exposure were measured using data from the U.S. Geological Survey, and blue space exposure was measured using data from the Joint Research Centre Global Surface Water dataset.

The researchers noted that they only had data on hospital records for fee-for-service beneficiaries, which means that some hospitalizations for beneficiaries who switched to managed care plans and back would have been missed.

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