Do mothers living in greenerneighbourhoods have healthier babies?E A Richardson

Agay-Shay and colleagues analyse a largeIsraeli birth cohort to address whetherbirth outcomes were related to levels of‘surrounding greenness’ (ie, density ofvegetation) around the mother’s place ofresidence.1 Their study builds on theexisting green space and health literature,2

and contributes to recent explorations ofwhether maternal exposure to green spacemight benefit the unborn child.3–7 Theresearch included almost 40 000 birthrecords, making it the second largest ana-lysis of green space and pregnancy out-comes to date. Importantly, this studyfocuses on an environmental factor withthe potential to support human healthand well-being, rather than on pathogenicenvironments.

The surrounding greenness of thematernal neighbourhood was positivelyrelated to birth weight and to reduced riskof low-birth-weight births, and these find-ings were not sensitive to whether green-ness was measured within 100, 250 or500 m of the home. Separate analyses bylevel of neighbourhood socioeconomicdeprivation revealed the strongest rela-tionships in the most deprived areas.Pregnancy length (gestational age andpreterm delivery) was not associated withsurrounding greenness in this study.

The study corroborates recent findingsfrom the USA, Spain and Germany.In these settings, researchers have consist-ently found that surrounding greenness ortree-canopy cover is related to foetalgrowth,3–7 but that associations with preg-nancy length or complications are absentor inconsistent.4–6 And while effect modi-fication by area-level deprivation has notbeen addressed elsewhere, the Spanishstudies report strongest relationshipsbetween surrounding greenness and birthweight for mothers with a low level ofeducation.4 5

Why surrounding greenness might berelated to birth weight remains unclear.Mechanisms proposed to explain theapparent beneficial influence mirror thoseproposed to explain green space and

health relationships more generally.In greener areas, it is hypothesised, preg-nant women may be more physicallyactive, have more social contacts and havelower stress levels, and thus the health ofthe fetus may benefit indirectly. Greenerareas also typically have lower levels of airpollution, noise and temperature, andreduced exposure to these environmentalstressors may either directly or indirectlybenefit foetal health. In studies that havetested these pathways, the beneficial rela-tionships have remained after adjustmentfor noise,3 air pollutants1 3–6 and mater-nal stress,3 although a partial mediatingrole for air pollutants is suggested in aSpanish study.5 The potential mechanismsmust be explored in further studies so thatthe health-promoting characteristics ofsurrounding greenness can be betterunderstood and enhanced in our commu-nities. The role of maternal stress couldbe particularly important, given the strongevidence of the restorative effects ofnature,8 and the widely acknowledgedphysiological pathways through whichstress might affect birth weight.9

In the field of environmental medicine,the term ‘exposure’ has been traditionallyapplied to passively experienced factorsthat influence health such as air pollution,noise or lead. In green space and healthresearch, however, the focus is on an envir-onmental factor that may influence healthboth directly and passively (via restorativepathways), and indirectly through the out-comes of health behaviours (being out-doors, physically active and/or mixing withothers). While this diversity results in mul-tiple pathways between green space andoutcomes, it is important to recognise thatthe primary health-influencing factor ofinterest is the green space itself, hence it isappropriate to refer to green space expos-ure. The measures employed by Agay-Shayand colleagues indicate the potential forhealth-relevant exposures to green space inthe residential setting, in a similar way tothat in which measures or estimates of airpollution concentrations in proximity to aperson’s residence are used to quantify thepotential for exposure to the pollutant.This broadening of the traditional nar-rower concept of exposure is beingadopted by the environmental medicineliterature.10

The ‘surrounding greenness’ measureused in these studies is derived from satel-lite imagery and aggregates all vegetatedfeatures, including public parks, privategardens, tree-lined streets and roadsideverges. Such a measure of ‘ambient’neighbourhood greenness may havehealth relevance for pregnant women ifthe health effects arise from the restora-tive or environmental amelioration prop-erties of nature.11 But the availability ofaccessible green spaces may be more rele-vant if the health benefits accrue primarilyfrom pregnant women being present orphysically active in green spaces.11

Agay-Shay and colleagues found that ameasure of neighbourhood availability ofgreen spaces was associated with preg-nancy outcomes in a similar way to sur-rounding greenness, thus could notdistinguish these potential mechanismgroupings. A Spanish study found thesame,4 but a German study found no sig-nificant relationship with local greenspace availability and concluded that thephysical activity pathway was thereforeunlikely.3 Testing of the causal pathwayscould be improved in future by incorpor-ating measures of green space type, aspublic and private spaces are likely tohave differing relevance.12

The conceptual reasoning behind themeasures of ‘greenness exposure’ in thisbody of work also needs strengthening.Accurately measuring an individual’sexposure to the environment inpopulation-based studies is generally notfeasible, hence researchers seek out appro-priate proxy measures. Greenness andpregnancy outcomes represent a relativelynew line of enquiry, with no pre-existingguidance as to how to measure greenspace exposure for pregnant women. Todate, researchers have opted for theoften-used technique of averaging withina variety of buffer zones—ranging from50 to 800 m—placed around the place ofresidence. Greenness within 50 m mightbe a proxy for the view from home, while500–800 m might better capture exposureduring a moderate walk in the neighbour-hood. Such differences have importantimplications for interpretation of resultsand inference as to the potential mechan-isms involved.

Currently, the greenness and pregnancyoutcomes literature has not consideredexposure to any greenness more than afew hundred metres from the maternalhome—exposures that may be importantfor pregnancy outcomes. In otherresearch, health benefits have been linkedto green space within 3 km of home, andgeneral and mental health have been

Correspondence to Dr EA Richardson, Centre forResearch on Environment, Society and Health (CRESH),School of GeoSciences, University of Edinburgh,Edinburgh EH8 9XP, UK; e.richardson@ed.ac.uk

Richardson EA. Occup Environ Med August 2014 Vol 71 No 8 527

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found to be more strongly related togreen space between 1 and 3 km fromhome than within 1 km.13 While a preg-nant woman’s mobility might be restrictedin the later stages of pregnancy, futureresearch should investigate exposure togreenness over a wider area.

Indeed, that surrounding greenness wasmost strongly related to birth weight forwomen of low socioeconomic status (SES)or living in low SES areas1 4 5 has beenattributed to lower SES groups spendingmore time in their home neighbourhood.4

Thus, the greenness measures used willrepresent exposure better for somewomen than others, and Agay-Shay andcolleagues’ assertion that any exposuremisclassification in their study is randomis not supported. Future work shouldexplore how best to capture pregnantwomen’s health-relevant experiences ofnatural environments.

Nonetheless, Agay-Shay and colleaguesmake a welcome addition to a small butgrowing literature about nature and preg-nancy outcomes. We know that healthacross the lifecourse is partly influenced inutero, hence understanding the role of theenvironment at this stage is crucial. Thiswork addresses a clear need for more con-sideration of factors that support humanhealth and well-being in this relationship,to balance the already substantial litera-ture regarding pathogenic factors. Future

studies should build on these foundationsand work to develop the underlying con-ceptual basis and methodology.

Funding EAR is supported by the European ResearchCouncil [ERC-2010-StG Grant 263501].

Competing interests None.

Provenance and peer review Commissioned;internally peer reviewed.

To cite Richardson EA. Occup Environ Med2014;71:527–528.

Received 17 March 2014Revised 10 April 2014Accepted 3 May 2014Published Online First 3 June 2014

▸ http://dx.doi.org/10.1136/oemed-2013-101961

Occup Environ Med 2014;71:527–528.doi:10.1136/oemed-2014-102163

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have healthier babies?Do mothers living in greener neighbourhoods

E A Richardson

doi: 10.1136/oemed-2014-1021632014

2014 71: 527-528 originally published online June 3,Occup Environ Med 

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