A study has shown that people who live in an environment with lots of greenery, parks and water have a lower risk of developing neurodegenerative diseases such as Alzheimer's and Parkinson's. This relationship still holds when factors such as income and air quality are taken into account.

The study was based on an analysis of hospital diagnoses of US citizens over the age of 65 between 2000 and 2016. The study looked at people who had no prior evidence of neurodegenerative diseases and who were newly diagnosed with Alzheimer's or related dementia or Parkinson's was asked. A total of 7,7 million people developed dementia and around 1,2 million developed Parkinson's during the observation period.

In addition to the diagnostic data, the researchers also used information about the insured person's age, gender, ethnicity, concomitant diseases and the postal code of their place of residence. A “green index” was created using satellite data, which depicts the vegetation density in summer. In addition, information on the frequency of parks and bodies of water was obtained from public sources. The green index had an average score of 0,52 on a scale of 0 to 1, with a higher score indicating more green. On average, almost 8% of the living space was taken up by parks and 0,5% by bodies of water.

After accounting for demographic factors, air pollution data, socioeconomic information, and structural differences in dementia and Parkinson's diagnoses in different US regions, there was a small but statistically significant reduction in dementia diagnoses in more green areas. For every 0,27 increase in the interquartile range (IQR) in the Green Index, there was a 5% reduction in dementia diagnoses. There was also a tendency for many parks and higher proportions of water to decrease the number of diagnoses, but these were not statistically significant.

An even clearer result was obtained for Parkinson's diagnoses. For every IQR increase in Green Index, the risk of Parkinson's was reduced by 6%. Risk was also reduced by 3% when park fraction increased by an IQR of 16%, and by a further 3% when water fraction exceeded 1%. There was a statistically significant correlation in all three natural parameters.

The association between the natural environment and neurodegenerative diseases was weaker overall in people living in urban areas, while poorer people appeared to benefit more from the natural environment around them. The researchers suggest that poorer residents may be more reliant on nature to exercise and relieve stress compared to wealthier people who have other options. However, it remains unclear why the effects are less pronounced in urban areas. Perhaps there is simply not enough nature there to have an impact on the risk of neurodegeneration.

There are other studies that support the research finding. Here are some examples:

1. A study from the Netherlands, published in Environmental Health Perspectives in 2020, found that people who live near green spaces had a lower risk of developing dementia. The study was based on data from over 300.000 people.
2. A study from Sweden, published in Scientific Reports in 2021, showed an association between being in nature and a reduced risk of developing Parkinson's disease. The results suggested that regular outdoor activities, such as walking or gardening, may have protective effects.
3. A meta-analysis of 11 studies, published in Aging & Mental Health in 2021, found that being closer to nature was associated with a lower risk of developing Alzheimer's. The analysis included data from over 17.000 participants.

These studies provide further evidence that a natural environment with green spaces can have a positive impact on the risk of neurodegenerative diseases such as Alzheimer's and Parkinson's.

Summary:

Jürgen Zender, June 2023