The Effects of Climate Change on Cognitive Health

Climate change has become a big topic in recent years; however, most of the discussion has focused on the immediate visible effects of climate change - more drastic weather events, loss of animal and plant species, increased physical health risks. While these are all important effects that we must address, it is also imperative that we recognize how climate change can impact our cognitive health.

Extreme Heat 

The past few months have been some of the hottest in history, resulting in a large spike in heat-related illnesses and deaths. 

Extreme heat can lead to excessive production of reactive oxygen species (ROS) and lowered antioxidant activity [1]. At low or moderate levels, ROS play an important role in normal neurological development and functioning; however, at high levels, ROS can cause the brain to go into a state of oxidative stress. Oxidative stress is associated with [2, 3]:

• Neuronal damage/death 
• Lipid peroxidation that damages membranes and generates neurotoxic compounds 
• Increased permeability of the blood-brain barrier (BBB), which is responsible for maintaining brain homeostasis and protecting the brain from outside toxins/pathogens [4]
• Affected cell functions (e.g. synaptic signaling, brain plasticity)
• Accumulation of neurotoxic proteins as a result of protein misfolding [5]
• Excitotoxicity (neuron damage/death caused by excessive exposure to excitatory neurotransmitters)

Increasing temperatures are also associated with activation of glial cells, which are involved in inflammatory responses in the central nervous system (CNS). Glial activation can cause damage to neurons and synapses through the release of proinflammatory and neurotoxic compounds, such as TNF-𝛼, IL-1β, and COX-2 [6]. 

All of these factors can affect cognitive health, such as impairing learning and memory [6] or increasing the risk of mental-health related outcomes and mortalities [7]. Additionally, they can contribute to the development of various neurodegenerative disorders. For example, misfolded tau and Aβ proteins are associated with Alzheimer’s disease, and the aggregation of 𝛼-synuclein is associated with Parkinson’s disease [5]. 

Older adults and children are two of the most vulnerable groups to heat-related health outcomes, as they have reduced abilities to regulate body temperature and deal with heat stress [8, 9]. In addition, a recent study found that repeated exposure to extremely high temperatures was associated with faster cognitive decline, particularly for socially vulnerable populations living in more disadvantaged neighborhoods [10]. This connection is still being explored; however, some potential explanations may be that these populations have no/little access to resources within their neighborhoods that can help with extreme heat (e.g. air conditioning, cooling centers, green spaces), and they have greater exposure to life events that negatively impact cognitive health (e.g. discrimination). 

Air Pollution 

Inhaled ultrafine particles (UFPs) can travel from the nose to the brain through the olfactory nerve or diffuse into the bloodstream through the lungs, affecting the function of several CNS cells [11, 12].

Microglia, in particular, respond to these pollutants with chronic activation, causing inflammation and oxidative stress in the brain. Oligodendrocytes (provide insulation for neurons) and neurons themselves may be affected by white matter lesions brought about by air pollution [13]. Additionally, UFPs can damage the blood vessels composing the BBB, as well as navigate across the barrier and increase inflammation [14]. 

These CNS effects have been shown to impact cognitive health in a variety of ways throughout the lifespan, including (but not limited to): 

• Delayed psychomotor development associated with air pollution exposure during pregnancy, particularly NO2 [15]
• Reduced cerebral cortex in several brain regions with exposure to fine particles during fetal life, which may be associated with impaired inhibitory control in school-age children [16]
• Prefrontal white matter lesions in children and significant deficits in fluid and crystallized cognition tasks [17]
• Diminished growth of working memory in children [18]
• Increased expression of COX-2 and Aβ42, as well as chronic oxidative stress through the generation of ROS, which may be associated with the formation of plaques and tangles (the hallmarks of Alzheimer’s disease) [19, 20]

Infectious Diseases 

Global warming has made it easier for infectious diseases to rapidly spread to different parts of the world. What does this mean for our cognitive health?

Some proteins produced during infections may cause neurotoxicity, affecting the functions of neurons or resulting in neuronal death. In addition, excessive local or systemic immune responses to the infections may produce proinflammatory cytokines that disrupt the BBB or affect neuronal activity [21]. To look at a more recent example, a 2023 study found that cognitive deficits were observed in individuals two years after being infected with SARS-CoV-2, particularly those who had more severe symptoms for longer periods of time [22]. 

This aspect of climate change is especially important to consider in older populations, who are at a higher risk of contracting infectious diseases. 

Climate Anxiety and Other Psychological Responses

Climate anxiety (also known as “eco-anxiety”) can be defined as distress in relation to the effects of climate change [24]. This term, as well as many others (e.g. eco-guilt, eco-grief), emphasizes the toll climate change has taken on individuals’ psychological wellbeing.

Individuals all around the world - most alarmingly, children and young people - report feeling worried about climate change and experiencing feelings of sadness, anxiety, anger, helplessness, and even guilt that impact their daily lives [25]. These negative climate-related emotions are associated with increased symptoms of insomnia and poorer mental health, both of which can affect cognitive health [26]. 

Takeaways

Climate change is something that is not only affecting our environment, but also our physical and cognitive health, particularly for our most vulnerable populations. It can be terrifying to think about how we can even begin to tackle this immense issue, but it is necessary that we take action now for the sake of our planet and our health. 

References

1. Jacobs et al., 2020: https://doi.org/10.1371/journal.pone.0242279 
2. Salim, 2017: https://doi.org/10.1124/jpet.116.237503 
3. Walter and Carraretto, 2016: https://doi.org/10.1186/s13054-016-1376-4 
4. Lochhead et al., 2010: https://doi.org/10.1038/jcbfm.2010.29
5. Bongioanni et al., 2021: https://doi.org/10.1016/j.envres.2021.111511
6. Lee et al., 2015: https://doi.org/10.1186/s12974-015-0324-6
7. Liu et al., 2021: https://doi.org/10.1016/j.envint.2021.106533 
8. Balmain et al., 2018: https://doi.org/10.1155/2018/8306154 
9. United States Environmental Protection Agency, 2023: https://www.epa.gov/climate-indicators/climate-change-indicators-heat-related-deaths 
10. Choi et al., 2023: https://doi.org/10.1136/jech-2023-220675
11. Elder et al., 2006: https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.9030 
12. Nemmar et al., 2001: https://doi.org/10.1164/ajrccm.164.9.2101036 
13. Block et al., 2012: https://doi.org/10.1016/j.neuro.2012.08.014 
14. Block and Calderon-Garciduenas, 2009: https://doi.org/10.1016/j.tins.2009.05.009 
15. Guxens et al., 2014: https://doi.org/10.1097/EDE.0000000000000133 
16. Guxens et al., 2018: https://doi.org/10.1016/j.biopsych.2018.01.016 
17. Calderon-Garciduenas et al., 2008: https://doi.org/10.1016/j.bandc.2008.04.008 
18. Alvarez-Pedrerol, 2017: https://doi.org/10.1016/j.envpol.2017.08.075 
19. Calderon-Garciduenas et al., 2004: https://doi.org/10.1080/01926230490520232
20. Moulton and Yang, 2012: https://doi.org/10.1155/2012/472751 
21. Du et al., 2023: https://doi.org/10.1016/j.bsheal.2023.04.002 
22. Cheetham et al., 2023: https://doi.org/10.1016/j.eclinm.2023.102086 
23. Murman, 2015: https://doi.org/10.1055/s-0035-1555115
24. Dodds, 2021: https://doi.org/10.1192/bjb.2021.18 
25. Hickman et al., 2021: https://doi.org/10.1016/S2542-5196(21)00278-3 
26. Ogunbode et al., 2023: https://doi.org/10.1007/s12144-021-01385-4