India has entered its summer, and the temperatures have been rising at an unbearable level, with heatwave warnings being issued across many cities. In fact, 19 of the 20 hottest locations on the planet are currently situated in India, according to data released by AQI.in. Surviving a heatwave has become more than just drinking water and staying indoors, because it is not always possible for everyone.
We speak to Dr Vimal Pahuja, MD, Associate Director, Internal Medicine & Metabolic Physician, Diabetes & Weight Management Clinic, Dr LH Hiranandani Hospital, Powai, Mumbai, to understand how heatwaves can affect the general public in the summer.
The earliest signs of dehydration are often subtle and frequently dismissed as general fatigue. Beyond
a dry mouth, people should look for brain fog or sudden irritability, a decrease in urination frequency, and dark-colored urine (resembling apple juice rather than lemonade). A common but ignored sign is a sudden headache or mild dizziness when standing up; these are the body’s ways of signalling that blood volume is dropping due to fluid loss.
The Rapid Progression to Heatstroke
Dehydration is the first domino. Once the body loses its ability to cool itself through sweat, the transition from mild dehydration to heat exhaustion can happen in under an hour of intense exposure. If the core body temperature continues to rise and hits 40°C (104°F), it becomes heatstroke, a medical emergency. At this stage, the thermostat in the brain breaks, and organ failure can begin within minutes. It is a terrifyingly fast progression.
The ‘Thirst Gap’ Paradox
Many people don’t feel thirsty until they are already 2% dehydrated. This happens because the thirst mechanism is a ‘lagging indicator’. In the elderly or those under extreme stress, the brain’s sensitivity to blood salt levels (osmolality) diminishes. By the time your brain screams ‘Drink’, your cellular functions are already struggling.
Who Are At High-Risk For Heatstroke?
The risk isn’t equal across the board due to physiological differences:
Children: They have a higher surface-area-to-mass ratio, meaning they absorb heat faster than adults, yet they sweat less efficiently.
Elderly: Ageing reduces the body’s ability to conserve water and sense temperature changes. Many also take medications (like diuretics) that exacerbate fluid loss.
Outdoor Workers: They face cumulative heat load. Their bodies never fully recover between shifts, leading to chronic strain on the heart and kidneys.
Women: They have higher heat-related mortality rates than men due to physiological factors, including lower sweat production, higher body fat, and hormonal fluctuations.
Long-Term Health Impacts of Heatwaves
Long-term exposure to extreme heat isn’t just about temporary discomfort. Over time, chronic heat stress can lead to chronic kidney disease (CKD) due to repeated micro-injuries to the renal tubules. It also puts a permanent strain on the cardiovascular system, increasing the long-term risk of hypertension and heart failure. We aren’t just treating a “hot day”; we are managing a long-term physiological toll.
Tips to understand heat issues
- The Pinch Test: Pinch the skin on the back of your hand. If it doesn’t snap back instantly (poor turgor), you are dehydrated.
- Don’t wait for thirst: Sip water every 20 minutes, even if you feel fine.
- Electrolytes matter: Water alone isn’t enough during heatwaves; you need to replace the salts lost through sweat.
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