Living by a busy road increases older people’s risk of depression, according to new research.
Dirty air has a “significant” impact on mental health – at the population scale, scientists warn.
The finding is based on almost nine million individuals in the U.S. – of whom more than 1.5 million developed the devastating disease.
Those exposed to high levels of fumes from traffic and industry were most prone.
Numbers of cases rose in tandem with exposure to nitrogen dioxide (NO2), toxic particles known as PM2.5s and ozone (O3).
The first two are spewed from engines, factories, wood-burning stoves and farming.
Ozone forms from their reactions with solar radiation on warm summer days.
Lead author Dr Xinye Qiu, of Harvard University in Boston, said: “In this cohort study among US Medicare enrollees, harmful associations were observed between long-term exposure to air pollution and increased risk of late-life depression.”
The over 64s were tracked for more than a decade with diagnoses identified from insurance claims.
Dr Qiu said: “All three pollutants were associated with an increased risk of developing depression.”
Computer models calculated exposures. His team also accounted for any annual residential address zip code changes over the follow-up years.
Dr. Qiu said: “Emerging evidence has suggested harmful associations of air pollutants with neurodegenerative diseases among older adults.
“However, little is known about outcomes regarding late life mental disorders, such as geriatric depression.
“Harmful associations were observed between long term exposure to air pollution and increased risk.”
Studies in mice have found air pollutants breathed in through the nose can travel to the central nervous system – causing inflammation in the brain.
This can trigger stress hormones linked to cognitive illnesses – including depression.
The process of aging may also release pro-inflammatory chemicals – exacerbating the effect on the brain.
Dr. Qiu said: “It is possible exposure to air pollution would first result in an increased risk of developing neurological disorders or other medical conditions in older adults.
“Although depression is less prevalent among older adults as compared with the younger population, there can be serious consequences such as cognitive impairment, physical illness and death.
“Therefore, it is of crucial importance to study preventable risk factors for developing depression among older adults to reduce the associated healthcare burden.”
Worldwide, exposure to air pollution has connected with an increased risk of adverse mental health outcomes, such as depression.
Dr. Qiu said: “To our knowledge, this study is the first to examine the associations between long-term exposure to air pollution and risk of late-onset depression incidence in a longitudinal setting over a study period of more than ten years.”
The study in JAMA Network Open has implications for public health management.
Dr. Qiu said: “We hope it can inspire researchers to further consider possible environmental risk factors such as air pollution and living environment for the prevention of geriatric depression, to understand the disease better moving forward and to improve the delivery of mental health care services among older adults.
“Due to the high prevalence and universal exposure to the ambient environment, if statistically significant associations could be established for modifiable risk factors of depression, such as air pollution, preventive population-based solutions could be applied to help control the disease burden through air quality regulation, emission control and greener planning for living environments.”
Results held after accounting for climate coexposures, neighborhood greenness, socioeconomic conditions, health care access and urbanicity level.
The World Health Organisation (WHO) guidelines recommend that PM2.5 should be kept under ten micrograms per cubic metre.
People living in UK cities are exposed to around 12.8 micrograms per cubic meter of average particulate matter.
Produced in association with SWNS Talker.
