Year

2024

Degree Name

Doctor of Philosophy

Department

School of Health and Society

Abstract

Background: As research interest in green space as a health resource increases, especially for the middle-to-older aged who experience the vast burden of non-communicable diseases (NCD), further clarification of concepts and tools is needed. First, the absence of a comprehensive composite score that measures healthy ageing across multiple health domains impedes a holistic understanding of how important green space is for living well longer. Second, despite evidence of the health benefits of green space in general, early and promising findings pointing to potentially greater returns on investment for mental health and mortality risk among individuals in socioeconomically disadvantaged positions warrant further investigation in the context of healthy ageing. Third, with most previous research examining green space as the overall ‘greenness’ of an area or the availability of parks, there is a need to provide more policy-relevant evidence on the types of green space that matter most and how their potential benefits may vary with respect to individual differences, such as by sex and among people with contrasting perceptions of their neighbourhood (e.g., differing views on safety). Collectively, these issues are important for long-term city planning especially when policy interventions seek to support people to grow old and live independently for as long as possible in community settings.

Aim: The aim of this thesis is to enhance understandings of the links between natural environments and healthy ageing. A key objective was to address the need for a comprehensive composite score that measures healthy ageing across multiple health domains to achieve this aim. I also examined associations between healthy ageing and various types of green spaces overall, and across individuals with contrasting socioeconomic circumstances. Next, I investigated the association of long-term exposure to green space types (grass, low-lying vegetation, or tree canopy) on healthy ageing and its functional capacity and resilience dimensions for participants who relocated or did not. Finally, I examined whether perceived neighbourhood attributes influence the association between green space types and health in old age, by testing associations between green space types and healthy ageing for people with differing neighbourhood perceptions.

Methods: This study used the secondary longitudinal data collected from the 45 and Up Study which is a comprehensive study on health and wellbeing in Australia. I focussed on individuals in this cohort who lived in the three largest cities in the state of New South Wales (NSW), Sydney, Newcastle, and Wollongong, to focus the investigation on urban green space. The development of the Healthy Ageing Score (HAS) is described in chapter four, where domain items were reduced based on correlations and underlying components were identified using confirmatory factor analysis. Chapter Five examined the associations between total green space and functional capacity, resilience, and healthy ageing scores, adjusting for factors like sex, couple status, income, and education. In Chapter 6 I conducted a longitudinal analysis considering participant relocation and residential stability to investigate the association between different types of green space and healthy ageing scores over time. Chapter Seven incorporates data from the Social, Environmental and Economic Factors (SEEF) study with green space data and neighbourhood perception measures. Regression analyses were performed to predict functional capacity, resilience, and the Healthy Ageing Score based on green space and neighbourhood perception, with interactions between perception items, green space measures, and sex.

Results: 80,826 out of 267,357 participants of the baseline survey had sufficient data for the computation of the proposed Healthy Ageing Score (HAS). After applying best practices for scale development, physical functioning, cognitive function, mental health, sleep, quality of life, balance, social connections, and overall health were retained. Functional capacity and resilience were uncovered as underlying latent structures. The HAS is the sum of the retained domain scores, with higher scores indicating a better health profile. Chapter 5 then calculated Healthy ageing indices for 34,085 participants in the Sax Institute’s 45 and Up Study (baseline 2006–2009), New South Wales, Australia. The sample was partitioned by socioeconomic and demographic characteristics and the association was assessed using regression analysis. Increasing grass cover was associated with declining health after the age of 45 years. Increasing low-lying vegetation (>10%) was associated with increased functional capacity but not resilience or healthy ageing. Areas that had 30% or more of greenery comprising tree canopy reported the highest mean functional capacity (6.60, sd 0.016), mean resilience (7.65, sd 0.007), and ultimately highest mean HAS (14.25, sd 0.019). Green space association with the healthy ageing score was higher for widows (β: 0.013, CI: 0.00, 0.03) compared to individuals with a partner (β: 0.003, CI: 0.00, 0.01). Also, the association was higher for participants earning less than $20k/annum (β: 0.015, CI: 0.01, 0.02) versus those earning >$70k (β: 0.007, CI: 0.00, 0.01). This beneficial association was higher for participants with no academic qualifications (β: 0.021, CI: 0.01 – 0.04) and for participants who are disabled (β: 0.028, CI: 0.00, 0.06) in their respective groups. In Chapter six longitudinal models of the association of green space types and healthy ageing showed that women who remained in the same neighbourhood over time had lower functional capacity (β; 95%CI: -0.10; -0.15, -0.05) and higher resilience (0.11; 0.08, 0.14) compared to those who relocated. Apart from age, personal characteristics did not explain the variation in healthy ageing outcomes for participants who moved. For participants who did not relocate, over 30% of grass cover was associated with decreased functional capacity (-0.22; -0.41, -0.04) and HAS (-0.31; -0.56, -0.05). Also, 5-9% of low-lying vegetation was associated with a decline in functional capacity (-0.09; -0.15, -0.03) and HAS (-0.09; -0.17, -0.01) of participants who stayed but improved resilience (0.28; 0.01, 0.55) of participants who relocated. Green space comprising over 30% tree cover appeared most beneficial for functional capacity (0.42; 0.31, 0.53), resilience (0.19; 0.13, 0.25) and HAS (0.60; 0.45, 0.75) for participants who remained in the same neighbourhood over time. For participants who relocated, over 30% of tree canopy was associated with improved functional capacity (0.33; 0.54, 0.62) but not resilience (-0.27; -0.97, 0.42) or their HAS 0.06; -1.25, 1.37).

The results of chapter seven showed that healthy ageing among older men and employed people exposed to increased tree canopy tended to be satisfied with their neighbourhood features. Positive perception of neighbourhood attributes was associated with improved healthy ageing outcomes. Perception of neighbourhood attributes, such as local shops and transport influenced the association between green space types and healthy ageing outcomes for different sexes. Increased tree canopy was shown to be beneficial for functional capacity, resilience, and overall healthy ageing score, while grass cover was negatively associated with the functional capacity for men and women who had a favourable perception of their neighbourhood. Women with a negative perception of their neighbourhood had the highest significant beneficial association of tree canopy with functional capacity (0.02; 0.01, 0.02) and healthy ageing score (0.02; 0.01, 0.03) compared to the functional capacity (0.01; 0.00, 0.02) and healthy ageing score (0.01; 0.01, 0.02) of men with a negative perception of the neighbourhood.

Conclusions: This research contributes a Healthy Ageing Score as a comprehensive tool to measure individual health profiles and identify factors influencing healthy ageing. It enabled the examination and comparison of individual health profiles (which can also be aggregated by groups) and the investigation of the factors that influence their chances of living healthy for longer. Increased tree canopy contributes more to the healthy ageing of disadvantaged groups than affluent groups. Targeted investment in green space provision, especially tree canopy >30%, can be readily leveraged to provide beneficial health outcomes and reduce the effect of socioeconomic disparity for disadvantaged communities.

This thesis recognizes several constraints concerning its applicability to the non-Australian context, potential over-representation of specific demographic groups, the omission of private and workplace green space exposure, the lack of consideration for green space quality and individual preferences, potential multi-residency of participants, and the failure to fully meet the assumption of a "well-defined intervention," thereby preventing causal interpretations despite the association between green space and healthy ageing.

FoR codes (2008)

0599 OTHER ENVIRONMENTAL SCIENCES, 1117 PUBLIC HEALTH AND HEALTH SERVICES

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.