June 15, 2015

expert reaction to exposure to green spaces at school and cognitive development in primary schoolchildren

A study of schoolchildren in Spain has been published in the journal PNAS, in which the authors aimed to examine the effects of exposure to green spaces on cognitive development. The authors report beneficial effects on aspects including memory and attentiveness with increasing levels of green space, which the partially attribute to reduction in exposure to air pollution.

Prof. Andy Jones, Norwich Medical School at the University of East Anglia, said:

“This is a well written paper, but the study is observational in design, meaning the researchers weren’t able to conduct any experiment. Whilst this is common, a resultant limitation is that we can’t be sure that any associations between cognitive development and greenspace exposure around where the children live are not due to factors the team haven’t considered.

“The researchers measured the association between cognitive development and the amount of vegetation present around the homes and schools of just over 2,500 primary school children aged between 7 and 10 years in Barcelona. They found that, over a 12 month period, working memory improved more and inattentiveness decreased more in children with more vegetation around their schools.

“They propose mechanisms by which their observed associations may be causal. However, it could be that the associations they observed are in fact related to factors other than those they considered. For example, the only measures they had on each family were the number of years of education the mother had, and it might be that families living in greener areas differ in other ways that mean their children develop faster.

“The data is a large sample of Barcelona schoolchildren. They measure cognitive development using widely accepted tests. However, their measure of greenspace is a simple measure of the amount of vegetation in the areas around where the children live and go to school. It does not therefore necessarily measure the amount of publicly accessible greenspace, such as public parks, in the neighbourhoods. Further, the researchers only know the amount of vegetation present, not if they children actual came into contact with it.

“The study has some limitations. The observational design means the associations could be due to factors the researchers haven’t considered.  The measure of greenspace used was the amount of vegetation in the neighbourhoods of the children and their schools derived from satellite images. It was not a direct measure of useable greenspaces, like public parks, although they will be included. The researchers know the amount of vegetation in the vicinity of the children, but not if the children actually came into contact with it. The only thing the researchers considered about the family was the level of education the mother had obtained. It might be that unmeasured family characteristics could at least partially explain the associations they observed.

“It is known that air pollution can limit cognitive development in children and that pollution levels tend to be lower in greener areas. The researchers tested to see if air pollution levels measured at the school explained the associations they had seen with greenspace. They measured air pollution using elemental carbon which is in an indicator of traffic pollution. They looked to see if levels of elemental carbon explained the association between cognitive development and greenspace. In other words, might better development in greener areas be due to lower air pollution? They found that elemental carbon at school explained up to 60% of the observed associations although this depended on the measures used. This suggests some, but not all, of the mechanism might be due to lower air pollution levels in greener area.”

Dr Ross Cameron, Senior Lecturer in Landscape Management, Ecology & Design at the University of Sheffield, said:

“This builds on previous studies that have suggested green space is important for cognitive development in children. It also is a fundamental principle in the ‘Forest Schools’ movement, where children are often more engaged and motivated when taught in a green and natural environment. This is the case even when the lessons are the same as would be experienced in a typical classroom. There are a number of theories as to why cognitive development can be aided by such green spaces – the environments themselves are more stimulating and general attention levels can be enhanced or students can feel more relaxed and at ease, so pay more attention to their studies. It could also be feasible that large areas of green space are helping absorb aerial pollutants, including CO₂, which at high concentrations can make people feel drowsy.

“The authors have taken a relative large scale epidemiology approach that strengthens the findings. (2,500 children). Data for a number of the parameters showed statistically significant results associated with increased areas of green space.

“Computer tests for evaluating memory and attention were used to determine cognitive development over a year – tests being conducted at 3 monthly intervals. (Such tests are now commonplace and considered valid).

“Children that attended schools with more green space (assessed by satellite for areas within the school boundaries and within 50 m of the school) showed greater cognitive development. For example, ‘superior’ working memory increased by 15 points in schools with a high proportion of green space compared to only 4 points in those where green space was limited.

“Responses were greater for the school than the home environment and the authors note rightly that pupils spend a higher proportion of daylight hours at school than at home which may explain the stronger responses. They do not assess, however, the hours spent outside directly exposed to the green environment.

“The authors suggest a causal link between air quality and green space – poor air quality reducing attentiveness and cognitive function – green space tending to improve local air quality. They admit however that this factor only seems to explain part of their correlations.

“Socio-economic factors are catered for, but there may be more subtle additional effects missing from the analyses and the authors acknowledge mental health of parents was not considered. For example, poorer areas tend to be less green but also have higher incidences of health problems. Such impacts on parents may also affect their children in terms of educational performance.

“The data for improvements in air quality are marked, but there may well be cofounding factors here not considered – we do not know what levels of polluted air quality pupils are actually exposed to – outdoor trees may only have a partial role to play in influencing air quality within the classroom for example. Also, tree canopies can actually enhance poor air quality in very localized spots, by not allowing air mixing. The data also ignores that certain trees species elicit hayfever through their pollen, with a very marked reduction in educational performance in the sufferers over that period!

“The authors acknowledge that further work is required to substantiate this claim.

“Indeed the benefits associated with increased areas of green space may relate to a range of factors in addition to air quality notably lower stress levels, greater opportunities for physical exercise (which can help both mental well-being and cognitive function), less aggression – (views of trees being shown to reduce domestic violence), lower noise levels and disruption, opportunities to engage with nature – enhanced interest and stimulation (at least for some pupils).”

Prof. James Crabbe, Supernumerary Fellow at Wolfson College, University of Oxford, said:

“This is a very interesting study on nearly 3,000 primary schoolchildren on Barcelona, indicating that the presence of ‘green spaces’ improves the children’s cognitive development. The investigators’ modelling suggests that a degree of the improvement may be due to the lack of traffic pollutants. While pollutant-free green spaces are undoubtedly important at early stages in education, they should be linked to enquiry- and skills- based curriculum development, in order to maximise the benefit to the child. It would be interesting to examine how the children in Barcelona could use their green spaces for curriculum development, and whether this produces improvements in their school tests.”

‘Green spaces and cognitive development in primary schoolchildren’ by Payam Dadvand et al. published in PNAS on Monday 15th June 2015.

Declared interests

Ross Cameron: Academic working on ecosystem service (and ‘dis-service’) delivery.

Author of a number of reviews on value (but also drawbacks) of urban greenspace.

Advise and give independent advice to green space organisations (AHDC, RHS, HTA) and government on above topics.

Have a number of funded grants, but none covering green space / air quality per se.

Member of Landscape Institute.

I am closely involved in the evaluation of urban green space, but it is not in my interest to see poorly-functional green space implemented, so objective scrutiny of latest research is important.

James Crabbe: I am an advisor to the Open Futures Trust

Andy Jones: No interests declared