A feasibility study on the association between residential greenness and neurocognitive function in middle-aged Bulgarians

Abstract

Recent research has indicated that exposure to residential vegetation (“greenness”) may be protective against cognitive decline and may support the integrity of the corresponding brain structures. However, not much is known about these effects, especially in less affluent countries and in middle-aged populations. In this study, we investigated the associations between greenness and neurocognitive function. We used a convenience sample of 112 middle-aged Bulgarians and two cognitive tests: the Consortium to Establish a Registry for Alzheimer’s Disease Neuropsychological Battery (CERAD-NB) and the Montreal Cognitive Assessment (MoCA). In addition, structural brain imaging data were available for 25 participants. Participants’ home address was used to link cognition scores to the normalised difference vegetation index (NDVI), a measure of overall neighbourhood vegetation level (radii from 100 to 1,000 m). Results indicated that higher NDVI was consistently associated with higher CERAD-NB and MoCA scores across radial buffers and adjustment scenarios. Lower waist circumference mediated the effect of NDVI on CERAD-NB. NDVI100-m was positively associated with average cortical thickness across both hemispheres, but these correlations turned marginally significant (P<0.1) after correction for false discovery rate due to multiple comparisons. In conclusion, living in a greener neighbourhood might be associated with better cognitive function in middle-aged Bulgarians, with lower central adiposity partially accounting for this effect. Tentative evidence suggests that greenness might also contribute to structural integrity in the brain regions regulating cognitive functions. Future research should build upon our findings and investigate larger and more representative population groups.

Outdoor green space exposure and brain health measures related to Alzheimer’s disease: a rapid review

“…Increased residential distance to natural outdoor environments was associated with longer cognitive test completion times, 62 and greater neighbourhood greenness was positively and inversely associated with dementia diagnoses (detailed in ‘older adults’ section below). 60 Greater neighbourhood greenness was cross-sectionally associated with better global cognition 72 and was associated with slower longitudinal decline on global cognition, reasoning and verbal fluency. 55 Additionally, greater neighbourhood green space was associated with greater cortical thickness in the prefrontal cortex, bilateral fusiform gyrus, left precuneus and insula, and right cuneus as measured via MRI.…”

“…62 No associations were found between self-reported visits or time spent in natural environments and visual attention/ executive processing, 62 and no associations were observed between greater greenness and cortical thickness of other brain MRI regions (eg, right cuneus and insula). 72 Lastly, inverse associations were found between 5-year change in neighbourhood greenness and reasoning. 57 Older adults (≥65 years).…”

“…71 Associations between greater neighbourhood greenness and better global cognition among middle-aged adults were mediated by lower waist circumference but not by systolic blood pressure, total cholesterol, glucose, air pollution (NO 2 ) or traffic-related noise. 72 The other four studies found no mediation of green space-brain health associations by physical activity, 53 55 62 social measures (eg, interaction, loneliness), 53 perceived mental health, 62 traffic noise annoyance, 62 worry about air pollution 62 or air pollution levels (ie, PM 2.5 ). 55…”

“…55 Additionally, greater neighbourhood green space was associated with greater cortical thickness in the prefrontal cortex, bilateral fusiform gyrus, left precuneus and insula, and right cuneus as measured via MRI. 72 Null associations were found between greater neighbourhood greenness/green space or 5-year change in greenness and measures of global cognition, 53 72 intelligence, 63 reaction time, 57 reasoning, 57 memory, 55 57 72 naming 72 and visual attention/executive processing. 62 No associations were found between self-reported visits or time spent in natural environments and visual attention/ executive processing, 62 and no associations were observed between greater greenness and cortical thickness of other brain MRI regions (eg, right cuneus and insula).…”

“…73 Tables 1-4 and online supplemental tables 1-4 summarise study characteristics and findings. Eight-two per cent (n=18) 9 54-58 60-64 66-69 [71][72][73] of studies were published on/after 2017 (range: 2012-2020). Seven studies (32%) were in the UK, four (18%) in China, three in Spain (14%), two each (9%) in the USA and Canada and one each (4%) in Bulgaria, Germany, New Zealand and multiple regions (Spain, UK, the Netherlands) (figure 2).…”