Greenspace and risk of obesity-related cancer in the UK Biobank cohort: An analysis of private residential gardens and other greenspace types.

Background: Cohort studies linking greenspace exposure to a lower risk of obesity-related cancer (ORC) are scarce. Existing evidence on site-specific cancers has predominantly relied on non-specific greenspace measures, including vegetation indices. We examined the associations of total greenspace, private residential gardens, and other greenspace types with the risk of being diagnosed with overall and site-specific ORC.

Methods: We used data from the participants in the UK Biobank recruited between 2006 and 2010 and censored until December 31, 2016. We defined greenspace variables using Ordnance Survey MasterMap™ greenspace categories. The incidence of ORC was ascertained through data linkage to cancer registries. Hazard ratios (HRs) and 95 % confidence intervals (CIs) were estimated using Cox proportional hazard models and adjusted for covariates. We conducted mediation and modification analysis by physical activity, serum 25-hydroxyvitamin D [25(OH)D], and particulate matter air pollution with an aerodynamic diameter ≤ 2.5 (PM) and nitrogen dioxide (NO), as well as subgroup analysis by covariates.

Results: Among 279,326 participants, 9550 developed ORC over a median follow-up period of 7.82 years. An increase in private residential gardens within a 100 m buffer was associated with a decreased risk of overall ORC (HR:0.92; 95 % CI: 0.88, 0.96), breast cancer (HR: 0.91; 95 % CI: 0.84, 0.98), and uterine cancer (HR:0.80; 95 % CI: 0.67, 0.96). There was no association between other greenspace types and ORC, except for uterine cancer. The association for ORC was partly mediated by NO and modified by physical activity levels, 25(OH)D, PM and NO, and sociodemographic factors, including sex and neighbourhood socioeconomic status.

Conclusion: Increased exposure to private residential gardens may lower the risk of being diagnosed with obesity-related cancer, particularly breast and uterine cancer. Future studies might move beyond considering greenspace quantity to explore functional types of greenspace exposure that should be prioritized for targeted health intervention and cancer prevention.