Helbich, M., Browning, M.H.E.M., Voets, D. and Dadvand, P. (2025) 'Adherence to the 3+30+300 urban green space rule and mental health, physical activity, and overweight: A population-based study in the Netherlands', Environment International, 202, 109643. https://doi.org/10.1016/j.envint.2025.109643.

A memorable planning rule acquires authority more quickly than the outcomes it is intended to secure. Using detailed urban-tree and green-space indicators linked to 2022 survey responses from 180,949 Dutch adults, Helbich and colleagues test the combined 3+30+300 rule against multiple health and behavioural measures through covariate-adjusted mixed-effects logistic regression. Only 16.4 per cent of respondents meet the composite rule. Adherence is associated with greater physical activity and lower likelihood of overweight, but not with the measured mental-health or other health outcomes. The negative findings are not a weakness to erase: they separate environmental provision from assumed psychological effects. Moreover, indicators assigned to residential addresses cannot account for all exposures accumulated in everyday movement. The work contributes a demanding principle of inference: preserve the distinction between a spatial planning threshold, the behaviour potentially associated with it and the health outcome actually observed. A neighbourhood archive should document those links without declaring them causal in advance.