The interplay between climate change and ageing: A systematic review of health indicators

Introduction The average lifespan has been greatly extended due to advancements in nutrition, technol- ogy, and medicine. Along with this, the declining birth rates have contributed to a rise in the population of individuals aged 65 years or older [1]. In 2019, there were approximately 703 million people in this age group worldwide, which is projected to reach 1.5 billion by 2050, an overall increase from 9 to 16% [2]. As individuals age, physical and mental declines occur, making older adults more vulnerable to external factors such as extreme tempera- tures and air pollution. According to a report by the United Nations (UN), both ageing and climate change are current urgent global concerns [3]. Several organizations have been col- laborating to find consensus and implement strategies for creating more sustainable and resilient societies and cope with the challenges of climate change. The Lancet Countdown, an international collaboration of 51 academic institutions and UN agencies, has been at the forefront of monitoring the health impacts of climate change. Their comprehensive research shows that the consequences of climate change extend beyond environmental issues and directly affect the health and well-being of populations, especially older adults. It empha- sizes the need for a health-centered response to address the complex and interconnected challenges of our time, ensuring that older adults and other vulnerable populations are ade- quately protected from the adverse effects of climate change while fostering more sustain- able and resilient communities [4].

In fact, climate change has far-reaching consequences for populations, affecting them in dif- ferent ways depending on where they live. Vulnerable communities in low-income regions often bear the greatest burden of climate change, characterized by limited resources, insuffi- cient infrastructure, and reduced adaptive capacity [5]. Older adults are especially vulnerable when it comes to mortality and morbidity. Studies show that heat-related mortality among older adults (aged 65 and over) has increased by 53.7% in recent decades [6]. Air pollution, as a driver/consequence of climate change, is responsible for 6.7 million deaths worldwide each year, making it the leading environmental cause of human morbidity and mortality. A quarter of these deaths occur in people over the age of 65, due to cardiovascular diseases [7, 8]. Climate change also affects cognitive function, and although the long-term effects are not yet well understood, there is a correlation between temperature variation and neurological diseases such as Alzheimer’s [9, 10]. It was already reported that older individuals with dementia or diminished cognitive function, coping abili- ties, and stress thresholds may struggle with environmental stressors, further exacerbating mental health conditions and increasing the risk of premature death [11]. It is important to emphasize that on a global scale, in 2016, neurological disorders stood as the foremost contrib- utor to disability, accounting for 276 million disability-adjusted life-years, and ranked as the

second leading factor responsible for mortality, causing 9 million deaths worldwide [12]. These climate changes have a range of adverse health impacts. Extreme heat can cause heat- related illnesses, worsen pre-existing conditions, and increase the risk of injury or death [13, 14]. Poor air quality can lead to respiratory and cardiovascular diseases, as well as other health problems [15]. Flooding can cause physical injury, water-borne diseases, and mental health problems, while vector-borne and water-related infections can lead to a range of illnesses and even death [16–20]. Food-related infections can also result in a higher burden on healthcare systems, with the associated hospitalizations, and even deaths [21, 22]. Furthermore, droughts can cause water shortages, which subsequently result in crop failures, economic downturns, and, consequently, the displacement of populations and even conflict [23]. Besides, climate change can also impact mental health, causing trauma, stress, anxiety, and social inequality, especially among vulnerable populations like those affected by extreme weather events and PLOS ONE Climate change, ageing and health PLOS ONE | https://doi.org/10.1371/journal.pone.0297116 April 24, 2024 2 / 17 Laboratory Institute for Health and Bioeconomy- i4HB, and also FCT under the scope of the project CAOP - PTDC/GES-URB/2038/2021, but no specific funding was used to this work. Competing interests: The authors have declared that no competing interests exist.