Are Healthcare Dollars Growing on Trees?

Examining 5+ million Northern Californians’ neighborhood tree canopy cover and healthcare costs

A recent scientific study has found that the more tree cover around a person’s home, the lower their healthcare costs — even when considering income and other factors. The findings suggest that every extra $1 invested in trees may save $18 in healthcare costs in the city and $10 in the suburbs.

Hundreds of studies suggest that regular contact with nature is vital for long-term health. Street trees and parks seem to confer protection from a variety of diseases, including diabetes, heart disease, and mental illness – even when considering income and other socioeconomic factors. Not surprisingly then, people without the protection of trees are less healthy and spend more on healthcare. See how the prevalence of conditions and diseases increases in nature-poor environments.

Childhood Obesity up by 15%

This section could also be a slider, going through all 8 diseases and conditions.

Coronary Heart Disease up by 25%

More info about CHD. Add final slide as a  link to the article on disease & conditions. 

Anxiety Disorders up by 44%

More info?

It’s true! Healthcare costs are 14% higher per person per year in areas without enough trees.  

Greening might offer an easy and affordable strategy for improving population health and reducing health costs – not to mention mitigating climate change.

Pullquote? Urban forests are great at generating a favorable return on investment (ROI). Every extra $1 spent on city trees helps to create significant savings on health care costs. Planting new trees and maintaining mature trees is an affordable option for reducing healthcare costs and easy to implement. Imagine what communities could do with those savings!

How was the study designed?

To test this assumption about greener neighborhoods, the researchers examined the health care costs for over five million members of Kaiser Permanente Northern California from 2003 through 2015. Next, the scientists sought to determine the amount of nature present or how ‘green’ an area was. This amount is measured using the Normalized Difference Vegetation Index (NDVI). NDVI uses satellite imagery of land cover provided by NASA and the United States Geological Survey (USGS). Link to the journal article. 

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Use the slider on the right to see differences in greenness, or as used in the study, NDVI (Normalized Difference Vegetation Index).

Learn more about the study. 

Image of diverse group of people

5,189,303 people

The study examined healthcare costs in a racially diverse population of over 5 million residents, with roughly a quarter Hispanic/Latinx, a quarter Asian/Pacific Islander, 7% Black, and four in ten non-Hispanic whites.

Overlay KPNC service area over 10 states to show size

Over 80,000 miles2

KPNC serves a geographic area larger than ten states. It encompasses diverse residential settings, including single-family suburban neighborhoods, dense urban cores, the wildland-urban interface, and more rural landscapes.

Show healthy people in well-treed neighborhood

Rigorous testing

The relationship between trees and healthcare savings held even when controlling for age, sex, race/ethnicity, household income, housing density, population density, and air quality.

What the scientists discovered.

The research found the assumption that living in a well-treed neighborhood reduced health care costs to be true. The relationship remained constant when the scientists took other factors into account, like age, sex, race/ethnicity, household income, housing density, population density, and air quality. The findings mean trees may offer an inexpensive and widely applicable option for improving public health and reducing health care costs.

Research suggests that every extra $1 invested in city trees may save $18 in healthcare costs.

A recent study by Kaiser Permanente and public health scientists has found the more tree cover around a person’s home, the lower their healthcare costs — even when comparing neighborhoods with the same income. The findings suggest that every extra $1 invested in city trees may save $18 in healthcare costs, and every extra dollar invested in trees may save $10 in healthcare costs in suburban areas.

Study Partners

Greenery within a few blocks of your home may save you up to $330/year on healthcare — for each person in your family!

The analysis indicates that residential greenness may reduce health care costs by improving health status. Findings suggest a threshold effect: health care costs drop only after greenness levels exceed NDVI values of 0.30. Greening might offer an inexpensive, widely applicable strategy for improving population health and reducing health costs.

#HealthyTreeHealthyMe

Help us to get more trees in the ground to create greener and healthier neighborhoods.

What you can do. 

Make Knowledge Contagious!

Share, share, share! Download these additional resources/graphics on trees and health. Share them with your friends and family. Include the hashtag #healthytreehealthyme. We have numerous images and captions messages backed by rigorous scientific research.

Show the Love.

Show your love of trees on your Facebook profile photo. We have created a series of frames you can add to your Facebook profile. Click here to add one automatically.

Let Them Know You Care.

Urban forests are a local issue, so you need to let your local elected officials know that having healthy trees in your community is essential. Click here to find contact information for your area and sample text for letters.

Resources to share. These need updating

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Do we want a more academic section that discusses the study?

Learn more about the study.

The researchers found that residential greenness like that provided by tree cover was associated with lower comorbidity and lower direct health costs in over 5 million individuals, even when accounting for income and a broad array of other factors. This relationship held for 13 years of costs, two different measures of greenness, and each of three distances from home. Members’ adjusted health care costs were 14% lower in the greenest than in the least green decile (relative rate= 0.86, 95% CI 0.85-0.87). Mediation analyses indicate that residential greenness may reduce health care costs by improving health status. Findings suggest a threshold effect: health care costs drop only after greenness levels exceed NDVI values of 0.30. Greening might offer an inexpensive, widely applicable strategy for improving population health and reducing health costs.

Study Population

The study population of 5,189,303 was larger than that of 28 of the 50 United States and represents not only non-Hispanic whites (42%) but also Hispanics/Latinx, Asian/Pacific Islanders, and Blacks in meaningful proportions (24%, 24%, 7% respectively, Bay Area Census, 2015).

Data Analyzed: Population

Health care costs for each member for 2003-20015 were assembled. These costs included expenditures both within and outside of KPNC, and included costs associated with: outpatient office visits to both primary care and specialty and other care; emergency department (ED) visits; mental health and substance abuse care; hospitalizations; laboratory services; radiology services; and pharmacy use. Health care costs did not include dental costs, patient out-of-pocket expenses, or certain administrative and overhead costs associated with health plan membership, such as marketing expenses. All costs were adjusted to 2016 dollars using the Consumer Price Index.

Setting

At over 80,000 square miles, KPNC’s service area is larger than the areas of 10 states. It encompasses not only single-family suburban neighborhoods but also dense urban cores, peri-urban fringes, and more rural landscapes. Climates and ecosystems vary from Mediterranean, high desert, and great basin to montane, alpine, and northwest coastal, 3 USDA Hardiness zones range from 5b in Placer and El Dorado Counties near Lake Tahoe to 10a in San Francisco County.

Data Analyzed: Setting

The primary measure of residential greenness was the Normalized Difference Vegetation Index (NDVI), calculated for land cover within 1000 m of a given member’s residential street address.

NDVI captures the literal greenness within 30 x 30 m resolution satellite images of land cover and is provided by NASA and the USGS. Greenness was categorized in deciles across individuals in the study with the lowest (least green) decile serving as the reference category.

Frequently asked questions about the study

How do you control for differences in things like education and income?

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Is any of the cost data broken out by age group - children, elderly?

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What about rural areas, or naturally heavily forested places?

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Regarding living in green space areas and the healthcare cost comparison being lower in greener neighborhoods, how does this reflect for people living in desert communities where there is open air and less urban density but maybe not much greenness?

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What do the different levels of tree canopy look like - say at 50%, 80% and 100% in Northern California?

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You mentioned that "more trees" resulted in positive outcomes- did you mean more canopy or actual more distinct trees?

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What about other community health factors like food deserts/transportation access/job quality. Were these included in the data analysis?

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Where can we get the in-depth results of the study?

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Where can we read the study?

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Are there any resources based on the research findings that I can share?

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References and other information

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ASSUMPTIONS

  • a completely intuitive guess: bringing our population from .25 NDVI to .45 NDVI will require, on average, a 30% increase in tree canopy
  • Each tree has a 5m crown on average
  • Planting and maintenance per tree is $100 over ten years (this assumes we can find one unpaved spot to plant in for each 267 sq m) 
  • population density in suburban areas of 1400 people/sq km
  • population density in urban areas of 2500 people/sq km

CALCULATIONS

  • It costs $100 to increase canopy by 80 sq m (one tree, 5m crown, area of crown is pi x 5^2)
  • A 30% increase in canopy corresponds to 1 new (80 sq m) tree for every 267 sq m of land (80/.3)
  • It will cost us $100 for every 267 sq m we want to green for health, or roughly 37 cents per sq m, over ten years
  • health care savings per sq km in suburban areas [$330 savings per person per year]*[10 years]*[1400 persons/sq km] = $4.62 M/sq km, or $4.62 per sq m 
  • health care savings per sq km in urban areas [$330 savings per person per year]*[10 years]*[2500 persons/sqkm] = $8.25 M/sq km, or $8.25 per sq m

KNOWN PROBLEMS WITH THE ASSUMPTIONS

  • I have no idea what a .2 to .45 NDVI difference corresponds to in tree canopy. It could be half as much, or two or three times more than 40% percent of land cover — but the calculation is fairly robust to poor estimates of this number. A 50% increase in canopy cover would only cost 62 cents/sq m, and a 25% increase would cost 31 cents/sq m — regardless, we’re talking less than a dollar per sq m, whereas the health care savings projections are on the order of multiple dollars.
  • this assumes 5m crown over all ten years across all different types/varieties
  • this assumes 100% tree survival (overly optimistic) and that all trees die when ten years is up (overly pessimistic)
  • estimates of population density for suburbs/cities vary greatly. 

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