Greenness, mortality and mental health prescription rates in urban Scotland - a population level, observational study

BACKGROUND: Recent studies have shown an association between vegetation around dwellings and mortality, with mental health as a possible mediator.

OBJECTIVES: Examine whether there is an association between greenness and mortality or greenness and the proportion of the population being prescribed drugs for anxiety, depression or psychosis in urban areas of Scotland.

METHODS: Two greenness maps were prepared based on Landsat 8 Normalised Difference Vegetation Index data from 2013 to 2016, one for summer and one for winter. Greenness was sampled from these maps around each of 91,357 urban postcodes. The greenness data was averaged by 4,883 urban Data Zones covering 71% of the Scottish population and compared with mortality and prescription rate data from the Scottish Index of Multiple Deprivation.

RESULTS: The areas least green in the summer were found to have higher mortality rates but no association was found between mortality and winter-greenness. The largest relative differences of mortality were around 9%. High levels of summer-greenness were associated with an increase in mental health prescription rates but areas with the highest differences between summer and winter-greenness had lower prescription rates than other areas. The largest relative difference in prescription rate was 17%. All models controlled for overall deprivation. It is hypothesised that the year round greenness of mown grass is associated with increased mental health prescriptions and obscures the benefits of other kinds of vegetation on both mortality and mental health.

DISCUSSION: There is an association between greenness and mortality and greenness and mental health. The association is both statistically significant and large enough to be of importance for policy making. Higher levels of non mown grass vegetation may be preferable for human wellbeing but more detailed understanding of the diversity of plant life in urban areas and how people related to it is required to make more specific recommendations.