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More tree cover linked to better mental health in older Australians

UNSW Sydney Centre for Healthy Brain Ageing (CHeBA)

Long-term study suggests greener neighbourhoods may help reduce depressive symptoms in later life

Living in neighbourhoods with more tree canopy may help protect against depression in older age, according to new research from UNSW Sydney's Centre for Healthy Brain Ageing (CHeBA) conducted in collaboration with Australian Catholic University (ACU).

The study, published in the Journal of Affective Disorders, followed more than 1,000 older Australians for up to 12 years and found that people who lived in areas with greater tree canopy experienced fewer depressive symptoms over time. The findings highlight the potential role of urban planning in supporting healthy ageing and mental wellbeing.

Researchers from CHeBA and ACU analysed data from 1,031 participants aged 70 to 90 years from CHeBA's Sydney Memory and Ageing Study, examining how neighbourhood features – including tree canopy, parkland, access to oceans, rivers and lakes, access to amenities and air pollution – were associated with changes in depressive symptoms over more than a decade.

The strongest and most consistent finding was that greater long-term exposure to tree canopy was linked to lower levels of depression.

"Trees provide far more than shade and visual appeal," said lead author UNSW Scientia Associate Professor Simone Reppermund.

"Neighbourhoods with more tree cover may encourage people to spend time outdoors, be physically active and connect with their communities – all of which are important for maintaining good mental health as we age."

Depression affects almost one in five adults over the age of 60 worldwide and is associated with poorer physical health, cognitive decline, reduced independence and lower quality of life.

Co-author and leading behavioural scientist with ACU's Mary MacKillop Institute for Health Research (MMIHR), Professor Ester Cerin, said the findings reinforce the importance of designing neighbourhoods that support healthy ageing.

"Creating greener neighbourhoods is a practical way to help foster healthier, more connected communities. While no single environmental feature can prevent depression, increasing tree canopy may contribute to neighbourhoods that encourage physical activity, social interaction and other behaviours that support mental wellbeing across the lifespan."

The researchers also investigated whether changes in neighbourhood environments over time influenced mental health. While some results initially appeared unexpected – including increases in tree canopy and reductions in nitrogen dioxide (NO₂) being associated with higher depressive symptoms – further analysis revealed these findings were largely explained by participants who had relocated during the study.

Many of those who moved did so because of declining health or into residential aged care facilities, where greener surroundings are often more common. The researchers say these life circumstances, rather than the environmental changes themselves, are the more likely explanation for the increase in depressive symptoms.

"Our findings reinforce that neighbourhood environments influence mental health in complex ways," said co-lead author Dr Annnabel Matison.

"Life events such as relocation, illness and the transition into residential aged care need to be considered when interpreting these relationships."

The study found little evidence that other neighbourhood features – including parkland, blue space, access to services or long-term exposure to low levels of air pollution – had a consistent impact on depressive symptoms after accounting for other environmental factors.

Senior author Professor Perminder Sachdev AM, Co-Director of CHeBA, said the findings add to growing evidence that healthy cities are important for healthy ageing.

"As Australia's population ages, creating neighbourhoods that support both physical and mental wellbeing will become increasingly important. Urban greening initiatives that increase tree canopy may offer benefits that extend beyond environmental sustainability to support brain and mental health."

The researchers say further studies in different populations and geographic settings are needed to better understand how neighbourhood environments interact with ageing, health and life transitions to influence depression.

The findings also reinforce the importance of considering environmental design alongside healthcare and social support when developing strategies to promote healthy ageing.

About the study

The study followed 1,031 community-dwelling older adults aged 70–90 years from CHeBA's Sydney Memory and Ageing Study for up to 12 years. Researchers from UNSW Sydney and Australian Catholic University assessed depressive symptoms using a modified 14-item Geriatric Depression Scale and measured neighbourhood characteristics – including tree canopy, parkland, blue space, built environment features and air pollution – within a one-kilometre walk of participants' homes.

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www.cheba.unsw.edu.au 

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Heidi Douglass
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