Spending Time in Nature may Protect against the Risk of Dementia

By Meeri Kim / Washington Post

13:33 JST, February 3, 2023

Spending time in nature – even as little as two hours a week – has been linked to several health benefits.

It seems to support healthy aging and has been associated with, among other things, improved cognitive function, blood pressure, mental health and sleep.

Now, a study of nearly 62 million Medicare beneficiaries suggests that nature may also help protect against the risk of developing certain neurodegenerative disorders.

The results revealed that older adults who lived in a Zip code with more green space had a lower rate of hospitalization for Parkinson’s disease, Alzheimer’s disease and related dementias such as vascular dementia and Lewy body dementia.

Blue space – bodies of water such as lakes, rivers and oceans – and the amount of land dedicated to parks in a given Zip code were also associated with fewer hospital admissions for Parkinson’s disease, but not for Alzheimer’s disease and related dementias.

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Nature can reduce stress levels

Why that is remains unclear, but leading theories propose that nature reduces our body’s stress levels while heightening our ability to focus. Proximity to forests, parks and other green outdoor common spaces can also encourage physical activity and provide opportunities to connect with other people.

Regular exercise and social interaction can help prevent Alzheimer’s disease and general cognitive decline, while chronic stress has been linked to an increased risk for dementia. Exercise may reduce the likelihood of developing Parkinson’s disease as well.

“We also know that, in general, air pollution and noise levels are lower in greener environments,” said study author Jochem Klompmaker, a postdoctoral research fellow at the Harvard T.H. Chan School of Public Health. “Some of these mechanisms may be related to Alzheimer’s disease and Parkinson’s disease.”

The protective associations of green space with hospitalization decreased after adjusting for air pollution, but still remained significant, implying that other factors are at play. The findings were published by JAMA Network Open in December.

“It’s not the first study to show this association between green space” and dementia/Parkinson’s, “but one of its big strengths is the extremely large study population,” said Anjum Hajat, associate professor of epidemiology at the University of Washington, who was not involved in the research. “No other study has been that large.”

Klompmaker and his colleagues looked at Zip codes and hospital admissions for all fee-for-service Medicare beneficiaries ages 65 and older who lived in the contiguous United States from 2000 to 2016.

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Health benefits of green space, blue space and park cover

To assess exposure to natural environments, they analyzed the amount of green space, blue space and park cover for each beneficiary’s residential Zip code. Green space was defined by the normalized difference vegetation index (NDVI), a measurement of the greenness of a parcel of land calculated using satellite imagery.

An NDVI of 1, for example, signifies the presence of dense green vegetation such as a forest, whereas urbanized areas with a scarcity of trees would score closer to 0. “NDVI captures green vegetation,” Klompmaker said. “That could be the grass in your backyard, trees on the street or even crops on agricultural lands.”

The researchers also used satellite imagery to gather blue-space values for water, while the percentage of park cover was based on the U.S. Geological Survey Protected Areas Database. Hospitalizations included those Medicare beneficiaries who had a primary or secondary discharge diagnosis of Parkinson’s disease, Alzheimer’s disease or related dementias.

The results confirm what other, smaller studies have observed in terms of nature and neurodegenerative disorders.

A 2022 study of four U.S. cities found that high residential green space was associated with a reduced risk of dementia among older adults. A 2021 review of 22 studies suggested positive associations between green space and brain health measures related to Alzheimer’s disease.

DuWayne Heupel, 69, lives in Colorado Springs, a nature lover’s paradise with over 9,000 acres of parkland and 500 acres of trails. “We have loads of green space in Colorado Springs,” Heupel said. “It definitely helps with my health, particularly my mental outlook.”

And in a 2020 study, residents of Vancouver, B.C., living close to roads had a greater incidence of Parkinson’s disease, Alzheimer’s disease and related dementias, but greenness seemed to have a protective effect.

“Based on the available evidence, we can say that the more contact with nature, the better,” said Payam Dadvand, associate research professor at the Barcelona Institute for Global Health, whose own research focuses on the effects of air pollution and green space on human health. His 2018 analysis of 6,506 older adults in the U.K. discovered slower cognitive decline over a decade-long follow-up period for those who lived in areas with more green space.

Researchers have theorized that exposure to nature provides health benefits by:

-Reducing harm – reducing exposure to air pollution, noise and heat.

-Psychological restoration – stress reduction and improved ability to concentrate.

-Facilitation of healthy behaviors – encouraging physical activity and social cohesion.

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Healing power of nature

Bill Furey, 61, of Placentia, Calif., recalls the exact moment he witnessed the healing power of nature. At age 12, he and his classmates, with their middle school science teacher, went on a hike to the bottom of the Grand Canyon.

Furey’s dad had died of pancreatic cancer a year earlier, and his mom thought the trip would be good for him.

“It was the first time I felt peace since my dad passed away, and it was the start of me wandering into the woods to find some soul care,” said Furey, who now leads Heritage Hiking Club (HHC), based in Orange County, Calif. “I’m definitely no scientist, but something magical happens when you get on your feet with dirt beneath your boots.”

He has met some of his best friends through the hiking group, and several members have even gotten married to each other, Furey said.

Josie Robarge of Banning, Calif., started regularly walking and running outdoors a little over a decade ago. Now, at 56, she hikes at least twice a week with fellow members of social groups such as HHC.

“They are the people you choose to do life with – encouragers, motivators, and friends that will make a wall around you if you have to use the restroom at Zion National Park and can’t make it back to the visitor’s center!” Robarge said.

If your neighborhood doesn’t boast an abundance of nature, visit a forest preserve or hiking trail, experts said.

The mounting evidence on green space being good for health should also lead national and local leaders to increase such space in urban areas and develop new natural spaces, Dadvand said.

“Getting out in nature is good for your health – not just in terms of dementia and Parkinson’s, but many different health endpoints we can assume are going to be improved by being outside and more connected with nature,” Hajat said.