Heatwave: what the heat really does to your body — and how to protect it.

6 min. read

02/07/2026

Canicule : ce que la chaleur fait vraiment à votre organisme — et comment le protéger.

Journal · Vitality & Protection

Heatwave: What Heat Really Does to Your Body

Extreme heat is more than just uncomfortable. It triggers a cascade of physiological imbalances: electrolyte, oxidative, cardiovascular, and neurological, which mobilize all of the body's resources.

37°C: The temperature your body defends at all costs

The human body is a thermal machine of remarkable precision. Core temperature must remain within a narrow window: between 36.5°C and 37.5°C for enzymes to function, neurons to fire correctly, and the heart to beat regularly. Above 38°C internally, alarm mechanisms activate. Above 40°C, cellular proteins begin to denature. A heatwave is a continuous war the body wages against external heat: often at the expense of everything else.

Thermoregulation mainly occurs through sweating: sweat glands produce sweat which, by evaporating, cools the skin and blood. But this mechanism comes at a cost. It requires constant hydration, sufficient electrolyte reserves, and a heart capable of pumping more blood to the periphery. When one of these pillars fails, the cascade of imbalances begins.

The 2003 heatwave in France caused over 15,000 deaths in two weeks: mainly elderly, isolated people in uncooled homes. This figure reminds us that extreme heat is a collective medical emergency, not just a summer discomfort. Understanding the physiological mechanisms involved is the first step to protecting oneself.

Physiological effects of heatwave on the body by system: BIOLOGYST Journal — Fig. 1: Physiological effects of heatwave by organ system

Scientific reference

Physiological and pathophysiological responses to heat stress

Bouchama A., Knochel J.P. · New England Journal of Medicine · 2002 · Vol. 346(25) · pp. 1978–1988

This reference review details the pathophysiology of heatstroke. It states that the response to thermal stress involves simultaneous activation of multiple systems: cardiovascular (redistribution of cardiac output), endocrine (HPA axis, cortisol), immune (pro-inflammatory cytokines), and oxidative (massive production of free radicals).

What this means concretely: it is not an isolable imbalance. It is a systemic physiological storm, where each system compensates for the failures of the others.

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"Heat doesn't just tire the body. It demands that it reorient everything: at the cost of the balance of each cell."

Five systems tested by extreme heat

Extreme heat affects the body in a cascade: each system tries to compensate for the imbalances created by the others, until reserves are exhausted. Here are the five most important mechanisms to understand.

The physiological effects of a heatwave

1

Dehydration and electrolyte loss

Sweating can reach 1 to 2 liters per hour in intense heat. Along with water, sodium, potassium, and especially magnesium, a key mineral for muscle contraction, nerve transmission, and heart regulation, are lost. As soon as −1% of body weight in water is lost, cognitive functions degrade. As soon as −2%, physical performance drops. As soon as −5%, the risk of cardiac events increases significantly.

2

Cardiovascular overload

To cool the body, the heart must pump more blood to the skin (peripheral vasodilation). Heart rate increases, blood pressure fluctuates, and myocardial work intensifies. In people with a history of cardiovascular disease, this overload can be fatal. The 2003 heatwave was associated with a 91% increase in cardiac mortality among those over 75.

3

Massive oxidative stress

Heat accelerates oxidative reactions at the cellular level. The production of free radicals (ROS) increases, exceeding endogenous antioxidant capacities (superoxide dismutase, glutathione peroxidase). Cell membranes, mitochondrial DNA, and enzymatic proteins are the first victims of this stress. This is one of the central mechanisms of cellular heat toxicity.

4

Sleep disturbances

Nocturnal thermoregulation requires the body temperature to drop by 0.5 to 1°C during sleep. Above 20–22°C in the bedroom, this cooling becomes impossible. Deep sleep (slow waves, NREM) and REM sleep are fragmented, and melatonin is disturbed. Chronic sleep deprivation during a heatwave amplifies physiological and immunological stress.

5

Renal and digestive impact

Urine concentration increases to conserve water, creating a favorable environment for kidney stones and overloading the kidneys. Digestion is slowed: digestive blood flow is redistributed to the skin for thermoregulation. Nausea, abdominal cramps, and loss of appetite are common. Insufficient fluid intake can precipitate acute renal failure.

−1%

Body water lost: immediate cognitive deterioration

×3

Free radical production in intense heat

20°C

Nighttime temperature: sleep disturbance threshold

300+

Magnesium-dependent enzymes

Magnesium: what leaves your body in sweat, and what it costs the body

Among all the electrolytes lost in sweat, magnesium is the one whose deficiency has the most extensive and underestimated consequences. Already deficient in 70 to 80% of the French population under normal conditions (according to SU.VI.MAX study data), this deficiency is massively exacerbated by sweating during a heatwave.

Magnesium is a cofactor for over 300 enzymatic systems. It participates in energy production (ATP-Mg stabilization), muscle contraction and relaxation (calcium channel regulation), nerve transmission (NMDA receptor inhibition), heart rhythm regulation, and the maintenance of deep sleep. Magnesium contributes to reducing fatigue, normal nervous system function, and normal muscle function.

Tachycardia on heatwave nights, nocturnal cramps, mental fog that persists despite rest: these manifestations are frequently reported during periods of intense heat. The literature links them to a decrease in magnesium status, although an isolated sensation cannot be attributed to it with certainty. In case of persistent discomfort, consulting a healthcare professional remains the right approach.

Cutaneous vasodilation: the role of L-Citrulline

Another often overlooked mechanism: cutaneous vasodilation necessary for heat dissipation depends on the production of nitric oxide (NO) by the vascular endothelium. L-Citrulline is described as a precursor to arginine, which is itself a substrate of NO synthase: it is in this capacity that available research is interested in it. During a heatwave, peripheral perfusion is not just a performance parameter: it is an element of thermoregulation.

Energy Daily Flow (No. 03) integrates this logic with 1,020 mg of L-Citrulline, taurine, and Setria® glutathione, in a stick format to be taken in the morning.

"70% of French people are already deficient in magnesium before summer. Heatwaves only worsen an already established deficiency."

Five formulas to support the body before, during, and after a heatwave

BIOLOGYST offers five supplements whose active ingredients are documented in relation to the physiological mechanisms described above. They can be used separately according to priorities, or combined.

No. 03 · Energy Daily Flow: L-Citrulline 1,020 mg + Taurine 510 mg

Key active ingredients: L-Citrulline 1,020 mg, taurine 510 mg, Setria® glutathione 250 mg, magnesium, vitamin C, vitamin D3, ginseng. Stick, 1 in the morning.

Role in a heatwave. L-Citrulline is a precursor to arginine, a substrate of NO synthase, the pathway involved in the dilation of cutaneous vessels and heat dissipation. Taurine and glutathione are the subject of research describing their role in the cellular response to thermal stress. Vitamin C contributes to protecting cells against oxidative stress and reducing fatigue.

Dosage: 1 stick in the morning in 500 ml of fresh water · ideal before and during the hot period.

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No. 04 · Magnesium Active+: 300 mg of magnesium

Key active ingredients: 300 mg of magnesium (bisglycinate + citrate + ATA Mg®), with taurine. Stick, 1 in the evening.

Role in a heatwave. Sweating increases magnesium loss; this stick provides 300 mg per dose. Magnesium contributes to normal muscle function, normal nervous system function, and the reduction of fatigue.

Dosage: 1 stick in the evening · can be doubled in case of intense sweating (sport, direct exposure).

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No. 06 · Power Hydra Flow: 100 mg of hyaluronic acid

Key active ingredients: 100 mg of ExceptionHYAL® Star hyaluronic acid and OVODERM® marine collagen. Stick, 1 in the morning.

Role in a heatwave. Hyaluronic acid is described in the literature for its ability to retain water in the extracellular matrix. This is the mechanism that available research documents. It does not replace fluid intake, which remains the basis.

Dosage: 1 stick in the morning in water · cure throughout the summer period.

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No. 13 · Antioxidant Defense: Quercetin 427 mg + Glutathione 375 mg

Key active ingredients: quercetin 427 mg, Setria® glutathione 375 mg, vitamin C 150 mg. Capsules, 2 to 3 in the morning.

Role during heatwaves. Vitamin C helps protect cells against oxidative stress, one of the central mechanisms of cellular toxicity caused by heat. Available studies describe the action of quercetin on low-grade inflammation, and of glutathione on maintaining cellular redox potential, particularly at the membrane and mitochondrial DNA levels.

Dosage: 2 to 3 capsules in the morning on an empty stomach · take during and after the heatwave period.

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No. 16 · Deep Sleep: Melatonin 1.8 mg

Key active ingredients: 1.8 mg melatonin, valerian, passionflower, Californian poppy, marjoram. Spray, 5 sprays in the evening.

Role during heatwaves. Melatonin helps reduce the time it takes to fall asleep, while nocturnal heat disrupts the circadian rhythm and prevents the drop in body temperature necessary for deep sleep.

Dosage: 5 sprays 30 minutes before bedtime · sublingual, hold for a few seconds.

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Heatwave Protocol: How to Combine Formulas

In the morning · cell protection

Energy Daily Flow (1 stick in 500 ml of cool water) + Antioxidant Defense (2 capsules on an empty stomach). L-Citrulline is part of the cutaneous vasodilation pathway described above; glutathione and quercetin are studied for their oxidative effects. Vitamin C, present in both formulas, helps protect cells against oxidative stress.

In the morning · in addition to fluid intake

Power Hydra Flow (1 stick). Hyaluronic acid is described for its ability to retain water in the extracellular matrix; this mechanism does not replace the water consumed throughout the day.

During the day

Regular hydration: minimum 1.5 to 2 liters of water, more if physically active or directly exposed to heat. Avoid alcoholic beverages and limit coffee (diuretic effect that increases electrolyte loss).

In the evening

Magnesium Active+ (1 stick in a glass of cool water): 300 mg of magnesium after a day of sweat loss. Magnesium contributes to normal muscle function and normal functioning of the nervous system.

Before bedtime

Deep Sleep (5 sublingual sprays, 30 minutes before sleep). Melatonin helps reduce the time it takes to fall asleep; the plants support warm nights.

“It’s not the heat alone that exhausts: it’s the cascade of deficits it creates. Anticipating is protecting.”

Essential actions that supplements do not replace

Food supplements are part of a global heatwave protection approach; they do not substitute for it. Fundamental actions remain non-negotiable.

Priority protective measures during a heatwave

Hydration

Drink at least 1.5 to 2 liters of water per day, without waiting until you feel thirsty (thirst is a sign of an already established deficit). In case of extreme heat or physical activity: 3 liters or more. Prefer cool water, not iced.

Cooling down

Spend at least 3 hours a day in a cool place (< 25 °C). Regularly spray skin and wrists. Take cool, not cold, showers or baths. Wet a cloth for the neck and temples.

Adapted diet

Prioritize water-rich foods (cucumber, melon, tomatoes, zucchini). Avoid heavy meals and difficult digestion, which increase internal heat production. Maintain sodium intake through a normal diet.

Vulnerable populations

Elderly people (> 65 years old), infants, people on diuretics or neuroleptics, those with kidney or heart failure: medical consultation is recommended during a heatwave to adapt treatments and monitoring.

Warning signs: medical emergency. Stop all activity and call 15 (SAMU) in case of: persistent temperature > 38.5 °C, confusion or disorientation, cessation of sweating despite the heat, loss of consciousness or seizures. These signs indicate heatstroke.

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Frequently Asked Questions

Why do heatwaves cause so much fatigue?

Because heat mobilizes five systems simultaneously: hydro-electrolytic, cardiovascular, oxidative, nervous, and renal-digestive. Sweating can reach 1 to 2 liters per hour in intense heat, and the heart has to pump more blood to the skin to dissipate heat.

Which mineral is lost most through sweating?

Magnesium is the electrolyte whose deficiency has the most widespread consequences. 70 to 80% of the French population already has a deficiency under normal conditions (SU.VI.MAX study), and it is a cofactor for over 300 enzymatic systems. Magnesium helps reduce fatigue and contributes to normal muscle function.

How much water should be consumed daily during a heatwave?

At least 1.5 to 2 liters of water per day, and 3 liters or more in case of extreme heat or physical activity. It is important to drink before feeling thirsty: the sensation of thirst signals an already established deficit. Cognitive functions deteriorate with as little as a 1% loss of body weight in water.

Why is it difficult to sleep when it's hot?

Sleep requires body temperature to drop by 0.5 to 1 °C. Above 20 to 22 °C in the bedroom, this cooling becomes impossible: deep sleep and REM sleep are fragmented, and melatonin secretion is disrupted.

What signs require calling 15?

A persistent temperature above 38.5 °C, confusion or disorientation, cessation of sweating despite the heat, loss of consciousness, or seizures. These signs indicate heatstroke: stop all activity and call 15 (SAMU).

Further analyses are available in the BIOLOGYST Journal, and details of active ingredients in Active Ingredients.

Precautions. Food supplement not a substitute for a varied and balanced diet or a healthy lifestyle. Do not exceed the recommended daily dose. Keep out of reach of children. In case of medical treatment, pregnancy, or breastfeeding, consult your healthcare professional. This article is general information and does not constitute medical advice.