Prolonged periods of high daytime temperatures and warm night-time conditions place cumulative stress on the human body, exacerbating these health issues.
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Climate change is not a future concern but a current crisis. The escalating global temperatures are causing more frequent and severe heat waves, as evidenced by a recent record of 52.9°C on the outskirts of New Delhi.
Projections indicate that global temperatures could increase by 2.5 to 2.9°C by the end of this century, underscoring the urgent need for immediate action. Over the past two decades, heat-related deaths among those over 65 have doubled, highlighting the severity of the situation. What is more, extreme heat events, which previously occurred once in 10 years, are now expected to happen more than five times as frequently. This significant increase in the frequency of extreme heat events is a cause for concern. Additionally, events that used to occur once in 50 years are projected to occur 14 times as often. Most of the world is expected to witness unprecedented heat conditions every other year by the middle of this century. This alarming trend demands immediate and concerted efforts to mitigate the impacts of climate change.
Vulnerable population
The increasing prevalence of non-communicable diseases and a growing ageing population mean more people are becoming vulnerable to the adverse effects of heat. Infants and young children, older people, outdoor workers, pregnant women, athletes, and people who are socially displaced or have substance use disorders are particularly at risk. Prolonged periods of high daytime temperatures and warm night-time conditions place cumulative stress on the human body, exacerbating these health issues. Additionally, overcrowded cities and poorly planned buildings contribute to urban heat generation. The loss of green spaces and the use of inappropriate housing materials further increase exposure to excessive heat, intensifying the challenges posed by climate change.
Temperature regulation
Human body temperature regulation operates through a combination of sweating, behavioural and autonomic responses, the latter being a part of the peripheral nervous system that controls involuntary physiological processes such as heart rate, blood pressure, respiration, and digestion. In response to heat stress, the human body redistributes blood flow towards the skin to enhance heat transfer from muscles to the skin, maintaining a core temperature of 37°C. Metabolic activity generates internal heat, which must be balanced with external environmental heat. High humidity levels complicate the dissipation of body heat through sweating, and when the internal and external heat loads become overwhelming, the body experiences heat stress. This can lead to a spectrum of
heat-related illnesses.
Heart & kidney strain
The redistribution of blood flow to the skin during heat stress increases the heart’s workload, requiring it to pump more blood faster and elevating the oxygen demand of the heart muscles. For individuals with pre-existing heart conditions, this heightened demand can create an imbalance between the oxygen supply and the needs of the heart muscles, potentially leading to cardiac ischemia (insufficient blood supply), infarction (cell death), and cardiovascular collapse. Large-scale analyses have shown that cardiovascular illnesses significantly contribute to deaths during heat waves. If not compensated with adequate fluid intake, increased sweat production decreases blood volume, placing additional strain on the kidneys. Chronic dehydration can lead to kidney fibrosis and chronic kidney disease, particularly concerning outdoor workers who are more exposed to heat.
Heat-related illnesses
The spectrum of heat-related illnesses ranges from mild conditions to severe heat stroke. In milder cases, excessive salt loss through sweating can lead to muscle cramps in the arms, legs, and abdomen during or after physical activity. These cramps manifest as muscle spasms, with an increased heart rate while body temperature remains normal.
Heat exhaustion may occur when the body’s water content or blood volume is reduced. This condition is characterised by fatigue, weakness, headache, nausea, increased heart rate, decreased urine output, and clammy, pale skin. Individuals not acclimatised to heat may experience dizziness and loss of consciousness, known as heat syncope, due to decreased blood supply to the brain.
Heat stroke is a life-threatening condition characterised by a body temperature exceeding 40°C, leading to multiple organ injuries, including damage to the brain, liver, and kidneys. This occurs when the body’s temperature regulation is disrupted, leading to an elevated body temperature. Heat stroke is often triggered by strenuous physical activity in hot conditions. It presents symptoms such as
decreased consciousness, agitation, vomiting, signs of injury to the heart, kidneys, and liver, and blood clotting abnormalities. These cases are dealt with external and internal cooling measures.
Understanding and recognising the symptoms of these heat-related illnesses are crucial for timely intervention and treatment. Early detection and appropriate response can prevent the progression from mild symptoms to severe, life-threatening conditions.
Public action
Dr Poornima Prabhakaran, Director of the Centre for Health Analytics Research and Trends (CHART), Trivedi School of Biosciences, Ashoka University and senior research scientist, Centre for Chronic Disease Control (CCDC), highlights the current reality of air pollution and heat-related illnesses. She references the Heat-health action plan, which envisages capacity building among healthcare professionals, including training medics for heat stroke and creating intensive care beds to treat heatstroke patients. Ahmedabad city was the first city in Asia to implement this in 2013. During the 2015 heatwave, its success was noted in significantly reducing fatalities. Only seven deaths were recorded in 2015, compared to a similar heatwave in 2010 that claimed 1,300 lives. This example underscores the effectiveness of proactive cross-sectoral inter-agency measures and well-structured health plans in mitigating the impact of extreme heat and saving lives.
Dr Priya Deshpande, associate professor of Community Medicine, Miraj, feels the need to prepare hospitals to tackle heat strokes and temperature reduction facilities like immersion tubs. Dr Poornima opines that the way forward besides sensitising the health workforce and strengthening health sector climate resilience is to link health infrastructure and local weather alerts to ensure early warnings regarding heat waves at the health facility level. This will increase the adaptive capacity within the health sector and facilitate a timely and suitable preparedness response to heat-sensitive illnesses.
How to beat the heat...
Avoid going out and engaging in strenuous activity during the hottest part of the day.
Spend 2-3 hours in a cool place during the day.
Use electric fans only when temperatures are below 40°C (104°F).
If using an AC, set the thermostat to 27°C (81°F) and turn on an electric fan to make the room feel 4°C cooler.
Stay hydrated by drinking one cup of water per hour, aiming for at least 2-3 litres daily.
Dress in lightweight, loose-fitting clothing, a wide-brimmed hat, sunglasses, and sunscreen to protect yourself from the sun’s rays.
(Dr Praveen Kumar Kaudlay is a consultant haemato-oncologist with a special interest in stem cell transplantation at Royal Wolverhampton NHS Trust, UK. He can be reached at praveen.kaudlay1@nhs.net.)