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Your Local Park Might Lower Your Risk of Dementia

Friday, July 14th, 2023

“Go for a little walk”, “pop outside for some fresh air”. Intuitively, we know that spending time outdoors is good for us. This is backed up by evidence that green space may be especially beneficial for brain health. Higher levels of tree canopy within a city (defined as the layer of leaves, branches, and stems of trees that cover the ground when viewed from above), has been associated with lower dementia risk.  Scientists are not too sure why this is.  A recent study set out to test some of the theories proposed[1].

A cohort study

The study accessed data from Australia’s largest ongoing study into health and ageing. The “45 and Up Study” has been following more than 250,000 people aged 45 and over from across New South Wales, since 2005[2]. The team focused on 109,688 of the participants who lived in one of the state’s three largest cities, and who had no report of dementia at the study start. The detection of dementia was then tracked from the day after the study start to the end of 2016, based on hospital admission information and mortality records.

A restorative environment

Consistent with past research, the study found that living in an area with greater than 20% tree canopy lowered the chance of developing dementia by 14% over 11 years. Increased physical activity, lower psychological distress, higher social support, and decreased incidence of diabetes all partially mediated, or explained, the dementia risk.  However, each one explained less than 6% of the total tree canopy-dementia association.  Meanwhile, levels of mediation via better sleep duration, less loneliness, or an absence of heart disease or hypertension were negligible or null.

The small percentage explained by the tested variables, suggests that other mediators may be more important. Larger tree canopies may lower dementia risk by reduced exposure to heat or air pollution, for example. The study design also encompasses some inherent error.  Relying on administrative health data for ascertaining dementia cases means that an unknown number of individuals with early-stage dementia would have been missed, plus those with dementia who had not yet been admitted to hospital or died.

Your postcode may impact your dementia risk

We cannot cure dementia. Thus, it is important to identify modifiable risk factors for the condition. As the evidence accumulates, “becoming one with nature’, starts to feel a little less corny. This study has made important progress in trying to identify possible pathways for the link between urban tree canopies and dementia.