BACKGROUND:
Exposure to ambient air pollution has been linked to poor cognitive performance in older adults, while residential greenness may be protective. However, most evidence comes from high-income countries, with limited data from South Africa. This study examined the association between green space and air pollution on cognitive function among older adults.

METHODS:
139 participants, aged 60 to 80 years, living in old age homes in the City of Johannesburg Municipality, Gauteng were included in the study. Cognitive performance was assessed using the Early Dementia Questionnaire (EDQ) and the Cambridge Neuropsychological Test Automated Battery (CANTAB), which evaluated memory, executive function, attention and psychomotor speed. Environmental exposures included ambient air pollutants (NO₂, SO₂) and residential greenness, quantified using normalised difference vegetation index (NDVI), within 100 m, 300 m, and 500 m buffers around participants’ residences. The associations between environmental exposures and cognitive function were modelled separately for EDQ score and CANTAB domains and clustered by facility, adjusting for age and sex.

RESULTS:
The prevalence of hypertension was 70.4% and probable early dementia was 55% (EDQ ≥8). Residential greenness was inversely correlated with NO₂ and SO2 concentrations across all buffer zones. Higher SO₂ exposure were associated with increased errors on paired association learning (PAL) indicating worse episodic memory (β = 28.31, p = 0.018), while higher NO2 was associated with slower reaction times (RTI) (β = -0.60, p = 0.003), indicating worse cognitive performance in the psychomotor speed and attention domains. No associations were observed for residential greenness within 100 m (per IQR NDVI increase) or NDVI at 300 m or 500 m buffers.

CONCLUSIONS:
Although based on a small sample size, findings indicate potential associations between NO₂ and SO₂ exposure and poor cognitive performance among older adults, highlighting the need for further investigation.