Background Evidence on the effects of exposure to green and blue spaces on childhood cardiometabolic health is inconsistent, limited and mostly cross-sectional.

Objectives To assess the associations of exposure to green and blue spaces, at birth, 4, 7, and 10 years (to identify vulnerable periods of exposure) and as longitudinal trajectories (to identify the longitudinal effect over time), with cardiometabolic health outcomes at 10 years.

Methods Participants are from Generation XXI, a population-based birth cohort from Porto Metropolitan Area, Portugal (n=4669). Residential normalized difference vegetation index (NDVI) and Euclidian distance to the nearest urban green and blue space were assessed at birth, 4, 7 and 10 years using geographic information systems and standardized by dividing the observed value by the standard deviation. Longitudinal trajectories of exposures from birth to 10 years were derived using latent class mixed models. At 10 years, we measured body mass index, fat mass index and android-to-gynoid fat ratio, blood pressure, and metabolic outcomes. We defined overweight/obesity by the World Health Organization, high blood pressure by the American Academy of Pediatrics and metabolic syndrome by the IDEFICS study.

Results No significant associations were observed between natural spaces exposure and body mass index, body fat content and distribution. We found an inverse association between distance to nearest blue space at birth and systolic blood pressure z-scores, and a positive association between distance to nearest green space at 7 and 10 years and metabolic syndrome score (p-values<0.05). Also, compared to children in the high stable trajectory of NDVI500m, those in the descending trajectory of NDVI500m presented a lower diastolic blood pressure z-score and metabolic syndrome score (p-values<0.05). However, after multiple testing correction, all associations lost statistical significance.

Discussion This study did not find robust associations between the exposure to natural spaces over key developmental periods and cardiometabolic health.

The authors have declared no competing interest.

Generation XXI (G21) was funded by Programa Operacional de Saude: Saude XXI, Quadro Comunitario de Apoio III and Administracao Regional de Saude Norte (Regional Department of Ministry of Health). This work was supported by FCT - Fundacao para a Ciencia e Tecnologia, I.P. through the projects with references UIDB/04750/2020 and LA/P/0064/2020 and DOI identifiers https://doi.org/10.54499/UIDB/04750/2020 and https://doi.org/10.54499/LA/P/0064/2020. Environmental exposures were assessed within the EXALAR 21 project (PTDC/GES-AMB/30193/2017) funded by the European Regional Development Fund (FEDER), through the Competitiveness and Internationalization Operational Programme, and by national funding from the Foundation for Science and Technology (FCT). Ana Isabel Ribeiro was supported by National Funds through FCT, under the programme of Stimulus of Scientific Employment: Individual Support within the contract CEECIND/02386/2018 (https://doi.org/10.54499/CEECIND/02386/2018/CP1538/CT0001). Susana Santos was supported by the European Union Horizon Europe Research and Innovation Programme under the Marie Sklodowska-Curie Postdoctoral Fellowship Grant Agreement No. 101109136 (URBANE). This study was supported by the European Union Horizon 2020 Research and Innovation Programme under Grant Agreement 824989 (EUCAN-Connect) and 874583 (ATHLETE).

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

All phases of the study complied with the Ethical Principles for Medical Research Involving Human Subjects expressed in the Declaration of Helsinki. The baseline and follow-up evaluations until 10 years were approved by the University of Porto Medical School/ S. Joao Hospital Centre Ethics Committee. At baseline and follow-up evaluations, all procedures were explained to participants, and informed consent was signed by one of the parents or legal guardians. The baseline evaluation was additionally approved by the Data Protection National Commission and the study follows the present EU General Data Protection Regulation under close supervision of the Data Protection Office of Institute of Public Health of the University of Porto (ISPUP).

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

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I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

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The data from Generation XXI are not publicly available due to privacy or ethical restrictions. The data can be made available for research proposals on request to the Generation XXI Executive Committee (generationxxiispup.up.pt). Further information about Generation XXI can be obtained via the Generation XXI website [www.geracao21.com] or by emailing generationxxiispup.up.pt.