The hidden health burden of environmental degradation: disease comorbidities and dryland salinity.

Previous studies have linked poor mental human health with environmental degradation, but none have assessed additional diseases that may co-exist with these mental disorders. In previous work, depression was found to be associated with a major form of environmental degradation; dryland salinity. However, little is known about diseases co-morbid with depression in this environmental setting. In rural Australia, dryland salinity is a major form of environmental degradation contributing widely to deterioration and non-viability of farmland. Using georeferenced health record data, Bayesian spatial methods were used to determine the relationship between dryland salinity and a range of human health outcomes. Initial modelling found an increased relative risk for asthma, suicide and ischaemic heart disease in relation to dryland salinity (adjusted for Indigenous and socio-economic status). However, in this follow-up study, a further evaluation of the role of co-morbidities in this population revealed that: (i) the presence of depression was consistently linked to residence in areas with high salinity and (ii) the association of asthma, suicide and heart disease with salinity was most likely attributable to the co-morbidity of the conditions with depression. Given the predicted increase in dryland salinity and the elevated relative risk of depression in impacted areas, the relative risk of the co-morbid conditions can be expected to increase in rural areas in the future, further adding to the burden of disease associated with environmental degradation.