Health effects of contact with nature
Description
There is a lot of scientific evidence that green areas contribute to improving the physical and mental health of local residents and people who visit these areas.
There are various mechanisms at play here:
- View of and contact with nature have positive effects on mental health (stress, depression).
- Proximity to nature stimulates outdoor recreation and exercise, with direct positive effects on health and derived positive effects through reducing obesity.
- Contact with nature ensures better development of children.
- Proximity to nature reduces the risk of overweight and obesity.
- In addition, nature offers a specific framework that is important for healthcare tourism.
There are also indirect health effects via air quality or reduction of noise pollution, but they do not fall under this category. These can be found on the health dashboard (expected end of 2022)
There is a certain overlap with the benefits of recreation. Recovery and rest belong to the main motives for recreational visits to green spaces, and this motive is closely linked to mental health effects. Recreational visits also lead to more exercise and this is one of the elements that lead to health effects. In the previous chapters we also considered these effects, but from the point of view of the recreationist and the local resident. The health benefits also benefit the rest of society, in the form of reduced healthcare expenditure and avoided absenteeism from the workplace. In this chapter we therefore pay attention to the health effects and related benefits for the patient, but also indirect effects for the rest of society.
Required input data:
- The number of residents in the area and within 100m from the area
- The number of residents between 100m and 1 km from the area
- The number of residents between 1 and 3 km from the area
Qualitative appreciation
The importance of the service is indicated by giving a score on the number of health effects an area has, divided by the size of the area (DALY/ha)
Quantitative valuation
Although there is a lot of scientific evidence that green space contributes to improving physical and mental health, there are fewer studies that allow these effects to be quantified. Dose-effect relationships are needed to quantify the health effects of environmental quality (presence of greenery). These types of studies look at the relationship between the presence of greenery in the immediate or wider environment of a citizen and his or her health status.
We base the quantification on the results of a multi-year scientific program in the Netherlands (Vitamin G - Maas, 2008). This research shows that there is a positive relationship between the amount of green area within a 1 km radius of the home and the reduced occurrence of 18 out of a total of 24 investigated diseases. The study is controlled for indirect demographic and socio-economic characteristics of the respondents and for the degree of urbanization. A positive effect has been found on heart disease, neck and back problems, depression, anxiety disorders, upper respiratory tract infections, asthma, infectious diseases of the gastrointestinal tract, urinary tract infections and diabetes. The relationship is greatest for mental illness.
For anxiety disorders, the negative health effects decrease by 5% for every 10% additional green space. For other health effects, the decrease ranges from 4% for depression to 1% for high blood pressure. We express this as the reduction in the number of DALYs (Disability-adjusted life years), being a reduction in the measure for the total burden caused by illness.
Table: Summary table of health effects of 10% extra green space within 1 km and 3 km of home.
| Health effects | DALY per 1000 inhabitants for 10% extra green space within a radius of | |
|---|---|---|
| 1km | 1 to 3 km | |
| Mental | 1.14 | 0.78 |
| Other | 1.32 | / |
| Total | 2.46 | 0.78 |
expressed in DALYs per 1,000 inhabitants
Because in the Nature Value Explorer we start from the green area instead of the home, we have to apply a number of additional calculations: We have converted the figures from the table above to DALYs for 1 ha of green space (agriculture, nature, forest) per 1000 inhabitants:
- 10% extra greenery in a radius of 1 km around the house is 31.4 hectares of extra greenery.
- 2.46 DALY for an additional 31.4 hectares
- 0.078 DALY for 1 ha of nature within a radius of 1 km
The same calculation is applied for greenery between 1 and 3 km from the home
If we start from the green area to calculate the number of DALY, not every hectare of this area will be within 1 km (respectively 3 km) of the homes. We have therefore calculated, based on the size of the areas, how much % of the total area should be included in the calculation.
Monetary appreciation
Economic valuation of health effects includes 3 types of benefits (De Nocker et al, 2010):
- Less healthcare costs: less expenditure on medicines, hospital costs, etc. Based on data for Flanders and/or Belgium.
- Less loss of productivity: both on the work floor and for home work, both based on Belgian/Flemish data.
- Less loss of prosperity due to suffering (both own suffering and suffering by family members, etc.): This is valued on the basis of data from European literature, in which this is derived on the basis of stated preferences (e.g. contingent valuation studies). These data are also used in European studies to substantiate environmental policy.
Recently, for the study on natural capital accounts, a value was calculated for valuing the reduction in “lost quality life years” through nature: 36,000 euros per DALY (De Nocker et al. 2020 ). This figure is based on a comparison of economic data for different diseases with the corresponding DALYs.
Assumptions
- Based on the available data, we cannot distinguish between the influence of the type of green space (forest, nature, agriculture) on health.
- The figures used start from the homes (residents). We have converted this into a method for starting from the green areas.
- We do not add health benefits to other cultural services. We view this as another way of valuing greenery.
Numbers to use
Table: Scores for qualitative valuation
| lower bound | score |
|---|---|
| 0 | 1 |
| 0.001 | 2 |
| 0.023 | 3 |
| 0.044 | 4 |
| 0.066 | 5 |
| 0.088 | 6 |
| 0.12 | 7 |
| 0.16 | 8 |
| 0.2 | 9 |
| 0.29 | 10 |
Source: ECOPLAN limit = number of DALY/surface area
Table: Quantitative assessment of health effects of 1 ha of extra greenery in DALY per 1000 inhabitants
| within a radius of | 100m | 1km | 1 to 3 km |
|---|---|---|---|
| Mental | 0.036 | 0.036 | 0.0031 |
| Other | 0.042 | 0.042 | 0 |
| Total | 0.078 | 0.078 | 0.0031 |
Table: Correction factor surface area
| To be used in calculation of number of DALY within 1 km | To be used in calculating the number of DALY between 1 and 3 km | ||||
|---|---|---|---|---|---|
| Lower limit of area size (ha) | % for residents within 100 m | % for residents between 100 m and 1 km | % for residents within 100 m | % for residents between 100 m and 1 km | % for residents between 1km and 3 km |
| 0 | 100% | 91% | 0% | 9% | 98% |
| 5 | 100% | 85% | 0% | 15% | 96% |
| 10 | 100% | 77% | 0% | 23% | 92% |
| 20 | 100% | 59% | 0% | 41% | 85% |
| 50 | 91% | 39% | 9% | 61% | 76% |
| 100 | 57% | 23% | 43% | 77% | 64% |
| 200 | 32% | 13% | 68% | 87% | 46% |
| 400 | 22% | 9% | 78% | 83% | 35% |
| 600 | 17% | 7% | 80% | 73% | 28% |
| 800 | 14% | 6% | 72% | 63% | 24% |
| 1000 | 12% | 5% | 65% | 56% | 21% |
| 1200 | 10% | 4% | 59% | 50% | 18% |
| 1400 | 9% | 4% | 53% | 45% | 16% |
| 1600 | 8% | 3% | 49% | 41% | 15% |
| 1800 | 7% | 3% | 45% | 38% | 13% |
| 2000 | 4% | 1% | 25% | 21% | 8% |
Monetary valuation is €36,000 per DALY
Translation to an indicator
Because DALY is not an obvious unit, we have translated it into the number of doctor visits someone would make if he/she developed the conditions that less greenery entails.
Parameter= 0.265924 doctor visits per 1000 inhabitants per hectare of green space (TEEBstad tool, 2016)
We also use the monetary valuation as such because this reflects the avoided health costs for society.
An example
For the example, we refer to the Dutch version of the manual.