TIE-UP BETWEEN HUMAN BODY AND GLOBAL TEMPERATURE FLUCTUATIONS

ABSTRACT

The relationship between human health and global temperature is a complex interplay influenced by climate change. This review explores the impacts of temperature fluctuations on human physiology, particularly focusing on heat stress, infectious diseases, and mental health. It examines how rising temperatures affect ectotherms, emphasizing their ecological and economic significance. Strategies for mitigating these impacts, such as dietary adaptations and urban planning interventions, are discussed. Understanding these connections is vital for informing public health policies and adaptive measures in the face of ongoing environmental changes.

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INTRODUCTION

The impact of global temperature changes on human health is increasingly recognized as a critical issue in public health and environmental science. With rising temperatures attributed to climate change, concerns have grown over the physiological and psychological effects on populations worldwide. This review delves into the various ways in which temperature fluctuations influence human well-being, including direct heat-related illnesses, changes in disease patterns, and mental health implications. Additionally, it examines parallels in the responses of ectothermic organisms to environmental changes, highlighting the broader ecological implications for biodiversity and ecosystem services. By understanding these connections, we can better prepare for and mitigate the adverse health effects of climate change.

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ECTOTHERMS

Ectotherms constitute the majority of terrestrial biodiversity, making the impacts of climate change on these organisms significant at organismal, community, and ecosystem levels. Predicting how species will respond to climate change is crucial for informed conservation decision-making, yet this has proven challenging. While it is known that ectotherms can adapt to climate change through both behavioural changes and physiological adjustments to altered environmental conditions, there is an urgent need for models that accurately predict how these changes will affect their distributions.

Understanding the relationship between ectotherm body temperature and air temperature is critical when using only the latter to make predictions about climate change impacts. This understanding is essential for assessing the effects on the most numerous and arguably most important terrestrial animals. Given the fundamental role of ectotherms, particularly insects, in food webs and in providing ecosystem services, their loss due to climate warming would have profound effects at the organismal and ecosystem levels, as well as significant economic implications.

Interestingly, this relationship can be observed in a basic form in the “Strange Situation,” where researchers monitor an infant’s behaviour in response to separation from their mother. During this ethological observation, infants’ skin temperature drops when the mother leaves the room, and peripheral temperature only returns to baseline once she returns. Similar effects are observed in adults; for instance, students' peripheral temperatures drop when they feel socially excluded. However, doubts remain regarding the extent to which social factors influence these physiological responses.

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RELATION BETWEEN HUMAN BODY TEMPERATURE

The optimal circadian core temperature for human cellular functioning, encompassing visceral, blood, and brain temperature, is approximately 37°C. At core temperatures below 0°C, cellular function ceases due to the freezing of water, while temperatures above 45°C cause enzyme denaturation. Climate change has posed a significant challenge to the human thermal system. Between 1850 and 2020, global near-surface temperatures have risen by over 1.2°C, with the most significant increase occurring after 1990. This rise has led to projections of more frequent and intense extreme weather events. Temperatures both below and above indifferent ambient temperatures can stress the thermal system, resulting in cold or heat stress. In particular, above-average ambient temperatures and heat waves have been associated with increased morbidity and mortality related to cardiovascular and respiratory diseases. Although the underlying mechanisms are not fully understood, they likely involve compromised cardiac oxygen delivery, dehydration, immune responses to cell death, and increased air pollution. Conversely, relatively little is known about the effects of ambient temperature changes on mental disorders, including potential underlying mechanisms.

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PSYCHOLOGICAL EFFECTS

The observational evidence for the psychological effects of ambient warmth and heat is slightly more comprehensive. Countries where the hottest month is relatively cold tend to be happier than those where it is comparably warm. Conversely, above-average temperatures show a robust relationship between temperature increases and interpersonal and intergroup conflict. A meta-analysis has shown that daily temperatures in the 99th percentile and heatwave defined as three consecutive days with maximum temperatures of at least 35°C are associated with a 2% and 9.7% increase in the risk of hospital admissions due to mental disorders, respectively. Additionally, the same analysis found that a 1°C increase in daily temperature is associated with a 1.7% increase in suicide rates. However, this meta-analysis could not differentiate between different exposure-outcome time lags, leaving it unclear whether specific time points and durations of heat exposure are particularly detrimental to mental health outcomes.

At body core temperatures between 37°C and 40°C, heat exhaustion occurs, characterized by poor judgment and irritability. Core body temperatures greater than 40°C led to heat stroke, which resembles severe hypothermia, causing delirium or coma. A psychological hypothesis suggests that heat-induced effects on mental health are mediated by violations of individual thermal comfort zones, which are between 15°C and 26°C outdoors and between 15°C and 32.5°C indoors. Notably, these reactions may be amplified by perceptions of heat as a societal and/or individual threat, contributing to climate anxiety.

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TEMPERATURE VARIATIONS

During exercise or ambient heat stress, elevations in deep body temperature to 38–40°C are normal and generally well tolerated, especially in heat-acclimatized or aerobically trained individuals. However, deep body temperature values exceeding 40°C increase the risk of heat injury and heat stroke. The denaturation of proteins in mammalian cells occurs within the range of 40–45°C, leading to protein inactivation, cell injury, and cell death.

Temperature impacts humanity on multiple levels, as evidenced by seasonal patterns in both health and disease. For instance, influenza epidemics peak every winter in temperate climates. Environmental models show that temperature is the strongest predictor of influenza peaks, with up to 84% accuracy in high altitudes. Besides the direct threat of heat, rising ambient temperatures are associated with increased rates of maladies such as infectious diarrhoea. Furthermore, the risk of new epidemics may increase by 20–50% in highly populated regions due to these temperature changes.

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DISEASES

A warmer climate could cause water-borne diseases to become more frequent, including cholera and diarrheal diseases such as giardiasis, salmonellosis, and cryptosporidiosis. Diarrheal diseases are already a major cause of morbidity and mortality in South Asia, particularly among children. It is estimated that one-quarter of childhood deaths in South Asia are due to diarrheal diseases. As ambient temperatures rise, bacterial survival time and proliferation will increase, potentially leading to a higher incidence of these diseases. Turbidity of freshwater is likely to further exacerbate this issue.

Rapid urbanization, industrialization, population growth, and inefficient water use are already causing water shortages in India, Pakistan, Nepal, and Bangladesh. Climate change will worsen the scarcity of available freshwater as annual mean rainfall decreases in many areas. Diarrheal diseases are largely attributable to unsafe drinking water and lack of basic sanitation; thus, reductions in the availability of freshwater are likely to increase the incidence of such diseases.

Cholera and malaria are significant public health concerns that have been exacerbated by environmental changes. Cholera, a water-borne diarrheal disease caused by Vibrio cholerae, has historically affected regions like India and Bangladesh and more recently Latin America and Africa. The bacterium thrives naturally in aquatic environments, with population peaks in spring and fall linked to plankton blooms. Cholera outbreaks correlate with rising sea-surface temperatures, altering the previous understanding that the disease had only a human reservoir.

Malaria, responsible for 400-500 million cases and over 1 million deaths annually, is driven by factors such as insecticide and drug resistance, population growth, land-use changes, and inadequate public health infrastructure. Environmental changes, including shifts in temperature, rainfall, and humidity, influence mosquito populations and the development of the Plasmodium parasite. In South Asia, malaria is already prevalent in countries like India, Bangladesh, and Sri Lanka, and climate change may further expand its range into higher latitudes and altitudes.

Emerging infectious diseases (EIDs) are those that increase in prevalence or pose a greater threat over time. These include newly diagnosed diseases and existing diseases that have mutated or adapted, exhibiting new characteristics such as different host targets, geographic spread, clinical presentations, epidemiological profiles, spread patterns, or resistance to treatments. Endemic diseases can also re-emerge, causing epidemics or increased prevalence. Notable EIDs in the last decade include Ebola in Africa, Middle East respiratory syndrome in the Middle East, and Zika, chikungunya, yellow fever, and dengue in the Americas. The CDC lists over 50 EIDs globally, including bovine spongiform encephalopathy, cholera, dengue fever, Ebola, HIV/AIDS, influenza, malaria, measles, MRSA, rabies, SARS, tuberculosis, and vancomycin-resistant Staphylococcus aureus.

In aquatic ecosystems, new parasite species frequently emerge, with Canada’s Laurentian Great Lakes basin experiencing an invasion of 182 non-indigenous parasite species, a new invader every 28 weeks. Rising seawater temperatures have caused severe diseases in coral reefs, leading to their decline. Coral reefs are vital as they provide shelter and food for many fish species. Additionally, increased water temperature reduces dissolved oxygen levels, causing significant disturbances in the aquatic ecosystem. (El-Sayed & Kamel, 2020).

Temperature fluctuations affect food-borne diseases. In continental Europe, 30% of salmonellosis cases occur when air temperatures are 6°C above average. In the U.K., food poisoning incidence strongly correlates with air temperatures from the previous 2–5 weeks. Hantavirus, transmitted to humans via rodent excreta, can cause serious and often fatal diseases. The emergence of hantavirus pulmonary syndrome in the southwestern U.S. in 1993 was linked to weather conditions, especially El Ni?o-driven heavy rainfall, which boosted rodent populations and increased viral transmission. (Patz & Olson, 2006).

Those of low socio-economic status are likely to be most affected by the health impacts of climate change, as they have the least adaptive capacity. As India's economy continues to expand, the growing middle class presents a unique situation. While rising out of poverty will improve sanitation levels and living conditions, increasing resilience to infectious diseases, it will also lead to higher consumption patterns that can initiate new health problems and lead to more carbon pollution

In developed countries, flood control efforts, sanitation infrastructure, and surveillance activities to detect and control outbreaks minimize disease risks caused by flooding. However, in developing countries, the increase in diarrheal diseases, cholera, dysentery, and typhoid is of specific concern. For example, after flooding in West Bengal in 1988, cholera was believed to be the cause of an outbreak of diarrhoea that resulted in 276 deaths. Numerous studies have linked previous floods in Bangladesh and parts of India with outbreaks of diarrhoea as well as respiratory infections.

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HEAT STROKES

Climate change is increasing global temperatures and intensifying extreme heat events, with the past seven years being the hottest on record. Recent heatwaves in Europe, India, and the Pacific Northwest of the United States have been significantly worsened by climate change. Heat stroke, a medical emergency marked by central nervous system dysfunction and a core body temperature over 40°C, has high mortality rates without prompt treatment. The rise in severe heat waves is leading to more heat-related illnesses and worsening heat-sensitive conditions. These illnesses are preventable, and clinicians play a crucial role in identifying at-risk patients, providing counselling, and recommending risk-reduction strategies.

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PATHOGEN ROLES

Pathogens encompass a broad spectrum of disease agents, including viruses, bacteria, parasites, germs, and fungi. Climate change impacts pathogens both directly, by influencing their survival, reproduction, and life cycles, and indirectly, through alterations in habitats, environments, or competitive interactions. Consequently, not only may the quantity of pathogens change, but also their geographic and seasonal distributions.

Temperature plays a crucial role in affecting disease dynamics by influencing pathogen life cycles. Pathogens typically require specific temperature ranges for survival and development. For instance, the maximum temperature thresholds of 22–23°C for mosquito development and minimum temperatures of 25–26°C for transmission of the Japanese Encephalitis Virus (JEV) are pivotal in their ecology. Excessive heat can increase mortality rates among certain pathogens. For malaria parasites like Plasmodium falciparum and Plasmodium vivax, development ceases when temperatures exceed 33–39°C. Rising temperatures also affect pathogen reproduction and the extrinsic incubation period (EIP). For example, the EIP for P. falciparum reduces from 26 days at 20°C to 13 days at 25°C.

Changes in climate patterns, particularly shifts in precipitation, further influence the dissemination of water-borne pathogens. Rainfall dynamics are critical for water-borne diseases as heavy rains can stir up sediments, increasing the concentration of faecal microorganisms during the rainy season. Conversely, unusual precipitation following prolonged droughts can trigger pathogen outbreaks by altering the environment's microbial balance. Droughts or low rainfall reduce river flows, concentrating effluent and enhancing water-borne pathogen concentrations.

Humidity fluctuations also impact infectious disease pathogens. Air-borne pathogens such as influenza viruses are sensitive to humidity conditions. Cold temperatures and low relative humidity favour the transmission and survival of influenza viruses. Similarly, changes in humidity affect water-borne viruses by limiting their survival near water surfaces due to drying effects. Additionally, humidity influences the development of vector-borne disease pathogens. For instance, humidity levels during the rainy seasons in regions like Yangon and Singapore favour the propagation of dengue virus in mosquitoes, contributing to outbreaks of dengue haemorrhagic fever.

So, climate change alters the dynamics of disease transmission by affecting temperature, precipitation patterns, and humidity levels, thereby reshaping the ecology and epidemiology of various pathogens globally.

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SUNSHINE AND WIND

Sunshine is a crucial climate variable that can impact infectious disease pathogens. For instance, the synergy between sunshine hours and temperature during cholera outbreaks creates favourable conditions for Vibrio cholerae multiplication in aquatic environments.

Wind plays a pivotal role in the spread of air-borne disease pathogens. Research indicates a positive correlation between dust particles and the survival or transportation of viruses. During Asian dust storms (ADSs), desert dust in the atmosphere has been linked to increased concentrations of cultivable bacteria, fungi, and fungal spores. Studies have shown significantly higher levels of influenza A virus during ADS days compared to normal days. Furthermore, research suggests that viruses can be transported across oceans by dust particles, facilitating transmission between distant hosts.

Sunshine and wind are critical climate factors influencing the ecology and transmission dynamics of infectious disease pathogens. Sunshine supports pathogen multiplication in water environments like those during cholera outbreaks, while wind, especially during dust storms, aids the dispersal and potentially long-distance transmission of air-borne pathogens, such as influenza viruses.

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STEPS TO PREVENT OUR BODY FROM GLOBAL TEMPERATURE

The outdoor microclimate in urban areas is shaped by prevailing weather conditions and influenced by local features like blue infrastructure (such as bodies of water) and green infrastructure (like vegetation). Bodies of water, with their high heat capacity and evaporative cooling effects, play a crucial role in moderating urban temperatures, particularly when water is in motion. Green infrastructure, including street-level vegetation and shaded parks, also helps cool urban areas by transpiring moisture and providing shade. Larger parks with ample tree cover can even create cooler microclimates known as urban cool islands, offering thermal relief to nearby residential and commercial zones.

Indoors, the widespread adoption of air conditioning using vapor-compression refrigeration technology has become the dominant strategy worldwide to combat heat and improve comfort. The global surge in air conditioning sales underscores its role in maintaining indoor temperatures amidst rising global temperatures. Beyond comfort, air conditioning significantly reduces heat-related health risks, such as heat strain and mortality, particularly in hospitals and workplaces. It enhances productivity and reduces labor costs, while recent adaptive comfort models have broadened the acceptable indoor temperature range to 21–29°C based on outdoor conditions.

In addition to air conditioning, cool roofs and innovative shading technologies are deployed to mitigate urban heat islands by reducing surface temperatures. However, these measures can introduce trade-offs in terms of cost, maintenance, and water usage. Strategies like utilizing advanced kinetic photovoltaic panels in urban design highlight ongoing efforts to optimize microclimate conditions while harnessing renewable energy. During extreme heat events, cost-effective and sustainable cooling strategies at the individual level, such as electric fans, offer effective relief by promoting convective heat loss. Despite their benefits, caution is advised with fan use in very high humidity conditions and temperatures above 35°C, where they may be less effective due to reduced sweating, particularly in older adults. Overall, balancing the implementation of cooling technologies with their environmental and economic implications remains crucial in urban planning to enhance resilience against rising temperatures and heat-related health risks.

The US Environmental Protection Agency advises against using fans when the heat index exceeds critical levels, which integrate temperature and humidity. Fans are less effective in very hot, dry conditions with a lower heat index compared to hot, humid conditions where they provide relief. A 2021 study proposes new temperature thresholds for safe fan use in public health policies: 39°C for younger adults, 38°C for older adults, and 37°C for older adults on specific medications. However, the effects of fan use on physiological heat strain with progressive dehydration or medication use remain unclear.

Heat enters indoor spaces through conduction, radiation, and ventilation. The external temperature of buildings depends on material properties, color, radiant heat load, and convective losses. Strategies like passive shading, green infrastructure, and urban ventilation can mitigate urban overheating. Addressing overall urban heat, not just the heat island effect, reduces air conditioning demand, waste heat, thermal pollution, and greenhouse gas emissions from mechanical cooling systems. Managing anthropogenic heat from vehicles, buildings, and industry requires planning and improved heat recovery technologies.

Cucumbers are synonymous with summer due to their high water content (about 95%) and are excellent for hydration. They also provide minerals like magnesium, potassium, and manganese, beneficial for the body. Cucumbers with skin intact offer the most nutrients and fiber, aiding digestion during hot months. Adequate hydration is crucial in summer to maintain healthy cells and protect against sun damage. Water intake from fruits and vegetables also contributes significantly.

Berries, such as strawberries, raspberries, and blueberries, are popular summer choices rich in vitamins (A, C, E) and antioxidants. These antioxidants reduce oxidative stress, which is common during summer due to increased activity. Berries contribute to optimizing the immune system due to their high vitamin C content.

Oranges are nutrient-dense, rich in vitamin C and potassium, essential for immunity and maintaining energy levels. Potassium supports muscle recovery and reduces fatigue, which are common in summer. Oranges also contain 80% water, aiding hydration and reducing the risk of muscle cramps.

Watermelon, containing phytochemicals like lycopene and vitamin C, offers anti-inflammatory, anticancer, and antioxidant properties. These phytochemicals reduce the risk of chronic diseases such as hypertension, diabetes, and cancer by inhibiting free radical formation. Watermelon's natural antioxidants make it a potential functional food ingredient, supporting traditional consumption habits. These foods and strategies can help mitigate the impacts of summer heat, improve health, and reduce environmental strain.

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CONCLUSION

In conclusion, the tie-up between human body and global temperature underscores the urgent need for proactive measures to address climate-related health risks. From improving heat resilience through urban planning and technological innovations to promoting dietary adaptations that enhance hydration and nutrition during hot periods, multiple strategies exist to mitigate the impacts of rising temperatures. Furthermore, enhancing our understanding of how temperature fluctuations affect both human populations and ectothermic species is crucial for developing effective public health interventions and conservation strategies. By integrating these insights into policy and practice, we can foster resilience and safeguard human health in a changing climate.

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BY: Mj arvind Balaji