Nature may protect against Alzheimer’s and Parkinson's, study finds

A sweeping review of Medicare records expands on research that shows spending time in nature may reduce the risk of a hospitalization for  Alzheimer’s, dementia and Parkinson's.

The findings suggest a more extensive link for Parkinson's than for Alzheimer’s but show potential prevention benefits for both.

“We can’t cure these diseases, so it’s important to identify modifiable risk factors so that people don’t get sick,” said lead author Jochem Klompmaker, a research fellow at Harvard's T.H. Chan School of Public Health. “Increasing physical activity, lowering stress and air pollution levels can be good for your health.”

The study reviewed hospital records for nearly 62 million Medicare members, who are 65 and older, or disabled. Using zip code data, the study looked at the impact of three different types of natural environments: parks, waterways and vegetation such as trees, crops or grass.

For Alzheimer’s, living in zip codes with just a little more than the average amount of vegetation was associated with lower rates of first time hospitalizations. For Parkinsons, all three types of nature — vegetation, parks and lakes, rivers or an oceanfront — were linked to avoiding a first hospital visit.

Klompmaker said the difference may have to do with air pollution. Some research associates air pollution with a higher risk of Alzheimer’s and dementia. Trees and some other plants reduce air pollution more effectively than open water or even some parks — which might be green spaces, artificial turf or paved areas. The research suggests living near a park or lake may not be as protective as living in communities with many trees.

Leafy neighborhoods can be more common for residents in higher income areas, but the findings did not vary significantly based on socioeconomic status. The effects of living near nature were found to be similar for men and women.

Researchers did find some differences based on race. For Black Medicare members, vegetation such as trees, crops or grass offered more protection from hospitalization for Alzheimer’s and Parkinson’s than it did for any other race. The effect of living near parks, rivers or ponds was similar for all races.

The study doesn’t address why Black Medicare members had slightly lower hospitalization rates. Klompmaker said it could be that they spend more time among greenery, that they are less likely to be diagnosed or some other factor.

Looking at the findings overall, Klompmaker said policymakers and urban planners should “create healthier environments so that people can live a healthier life.”

There are some important nuances to keep in mind. Trees can clean and cool the air, but they also release pollen which Klompmaker’s earlier research shows can increase hospitalizations for people with allergies, especially in urban areas. That same study found that despite the drawbacks for allergy-sufferers, vegetation such as trees may protect against a hospital admission for heart problems.

The study does not analyze why exposure to nature appears to protect against a first time hospital stay for Alzheimer’s or Parkinson’s, but prior research shows exposure to nature can have a calming effect, boost immunity, and improve memory — factors that may be relevant for Alzheimer’s and Parkinson’s disease.