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

6 min. read

02/07/2026

VITALITY & PROTECTION · JOURNAL

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

Extreme heat is not just uncomfortable. It triggers a cascade of physiological imbalances — electrolyte, oxidative, cardiovascular, and neurological — that mobilize all of the body's resources.

— WHAT YOU NEED TO KNOW

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 internal temperature, alarm mechanisms activate. Above 40°C, cellular proteins begin to denature. A heatwave is a continuous war the body wages against external heat — often to the detriment of everything else.

Thermoregulation primarily occurs through sweating: sweat glands produce sweat which, as it evaporates, 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 killed over 15,000 people in two weeks — mainly elderly, lonely individuals in uncooled homes. This figure reminds us that extreme heat is a collective medical emergency, not just a simple summer discomfort. Understanding the physiological mechanisms at play is the first step to protecting oneself.

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

Access publication → https://doi.org/10.1056/NEJMra011089

This seminal review details the pathophysiology of heatstroke. It establishes 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). It is not an isolable imbalance — it is a systemic physiological storm.

“Heat doesn't just tire the body. It demands that the body reorient everything — at the cost of the balance of every cell.”

— WHAT HAPPENS IN THE BODY

Five systems put to the test
by extreme heat

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

THE PHYSIOLOGICAL EFFECTS OF 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. At just -1% of body weight in water, cognitive functions decline. At -2%, physical performance drops. At -5%, the risk of cardiac events significantly increases.
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 workload intensifies. For individuals with a history of cardiovascular issues, this overload can be fatal. The 2003 heatwave caused 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 heat's cellular toxicity.
4. Sleep disturbances	Nighttime thermoregulation requires 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-wave, NREM) and REM sleep are fragmented, and melatonin is disrupted. 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 slows down — as 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 kidney failure.

— WHAT HAPPENS IN THE BODY

Five systems put to the test
by extreme heat

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

THE PHYSIOLOGICAL EFFECTS OF THE 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. At just -1% of body weight in water, cognitive functions decline. At -2%, physical performance drops. At -5%, the risk of cardiac events significantly increases.
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 workload intensifies. For individuals with a history of cardiovascular issues, this overload can be fatal. The 2003 heatwave caused 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 heat's cellular toxicity.
4. Sleep disturbances	Nighttime thermoregulation requires 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-wave, NREM) and REM sleep are fragmented, and melatonin is disrupted. 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 slows down — as 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 kidney failure.

-1 %

WATER = IMMEDIATE COGNITIVE DETERIORATION

X3

FREE RADICAL PRODUCTION IN INTENSE HEAT

20°C

NIGHTS = SLEEP DISRUPTION THRESHOLD

300+

MAGNESIUM-DEPENDENT ENZYMES

— MAGNESIUM: THE MOST CRITICAL MINERAL

What you lose in sweat
and what it costs your body

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

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. A magnesium deficit during a heatwave simultaneously leads to: muscle cramps, profound fatigue, nervous irritability, sleep disturbances, and cardiac vulnerability.

The tachycardia on heatwave nights, the nocturnal cramps that wake people from their sleep, the mental fog that persists despite rest — these very common symptoms are largely direct signs of functional hypomagnesemia. And they are easily correctable.

Another often overlooked mechanism: cutaneous vasodilation necessary for heat dissipation depends on the production of nitric oxide (NO) by the vascular endothelium. L-Citrulline — a precursor of arginine, which itself is a substrate for NO synthase — directly optimizes this mechanism. During a heatwave, effective peripheral perfusion is not just a performance advantage: it is an element of thermoregulation. Energy Daily Flow (No. 03) integrates this logic with 1,020 mg of L-Citrulline, taurine for cardiac stability, and Setria® glutathione for oxidative protection — in an easy-to-take stick format for the morning.

"70% of French people are already magnesium deficient before summer. The heatwave only exacerbates an existing deficit."

— THE BIOLOGYST RANGE

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

BIOLOGYST offers five supplements whose active ingredients directly address the physiological imbalances induced by extreme heat. They can be used separately according to priorities or combined for overall protection.

NO. 03

ENERGY DAILY FLOW

Stick · 1/morning

NO. 04

MAGNESIUM ACTIVE+

Stick · 1/evening

NO. 06

POWER HYDRA FLOW

Stick · 1/morning

NO. 13

ANTIOXIDANT DEFENSE

Capsules · 2-3/morning

NO. 16

DEEP SLEEP

Spray · 5 sprays/evening

KEY ACTIVE INGREDIENT

L-Citrulline 1,020 mg + Taurine 510 mg

Setria® Glutathione 250 mg + Mg + Vit C + D3 + Ginseng

KEY ACTIVE INGREDIENT

300 mg magnesium

Bisglycinate + citrate + ATA Mg® (with taurine)

KEY ACTIVE INGREDIENT

100 mg hyaluronic acid

ExceptionHYAL® Star + OVODERM® marine collagen

KEY ACTIVE INGREDIENT

Quercetin 427 mg + Glutathione 375 mg

Setria® + Vitamin C 150 mg

KEY ACTIVE INGREDIENT

1.8 mg melatonin

Valerian + Passionflower + Eschscholtzia + Marjoram

ROLE IN HEATWAVE

L-Citrulline boosts NO (nitric oxide) production—the signal that dilates cutaneous vessels to dissipate heat. Taurine and glutathione protect the heart and cells from heat stress.

ROLE DURING HEATWAVE

Compensates for sweat losses. Prevents cramps, muscle tension, and tachycardia. Stabilizes the nervous system and promotes sleep despite the heat.

ROLE DURING HEATWAVE

Hyaluronic acid retains water in tissues. During a heatwave, it maintains deep hydration of mucous membranes, skin, and joints where water intake alone is insufficient.

ROLE DURING HEATWAVE

Neutralizes the massive oxidative stress induced by heat. Protects cell membranes and mitochondrial DNA. Quercetin reduces low-grade inflammation exacerbated during a heatwave.

ROLE DURING HEATWAVE

Compensates for circadian disruption caused by nighttime heat. Melatonin helps lower body temperature. Plants promote deep sleep even on hot nights.

DOSAGE

1 sachet in the morning in 500 ml of fresh water · Ideal before and during the hot period

DOSAGE

1 sachet in the evening · Can be doubled if intense sweating (sport, direct exposure)

DOSAGE

1 sachet in the morning with water · Use throughout the summer period

DOSAGE

2-3 capsules in the morning on an empty stomach · Use during and after the heatwave period

DOSAGE

5 sprays 30 min before bedtime · Sublingual, hold for a few seconds

View Energy Daily Flow →

View Magnesium Active+ →

View Power Hydra Flow →

View Antioxidant Defense →

View Deep Sleep →

HEATWAVE PROTOCOL — HOW TO COMBINE FORMULAS

In the morning	Energy Daily Flow (1 sachet in 500 ml of fresh water) + Antioxidant Defense (2 capsules on an empty stomach). L-Citrulline optimizes cutaneous vasodilation to dissipate heat from the start of the day. Glutathione and quercetin protect cells from oxidative stress.
In the morning	Power Hydra Flow (1 sachet) to maintain deep tissue hydration. Hyaluronic acid retains water in tissues—an essential complement to oral hydration during periods of high heat.
During the day	Regular hydration: 1.5 to 2 liters of water minimum, more if physically active or directly exposed. Avoid alcoholic beverages and limit coffee (diuretic effect increases electrolyte loss).
In the evening	Magnesium Active+ (1 sachet in a glass of fresh water): compensates for daily magnesium losses through sweat, relaxes muscles, prevents nocturnal cramps, and prepares the nervous system for sleep.
Before bedtime	Deep Sleep (5 sublingual sprays, 30 min before sleep): melatonin helps lower body temperature and induce sleep despite the heat. Sedative plants support deep sleep even on warm nights.

“It’s not the heat alone that exhausts — it’s the cascade of deficits it creates. To anticipate is to protect.”

— ESSENTIAL ACTIONS

Basic recommendations
that supplements do not replace

Food supplements play an important supportive role — but they are part of a global heatwave protection strategy. Fundamental actions remain non-negotiable:

PRIORITY HEATWAVE PROTECTION MEASURES

Hydration	Drink a minimum of 1.5 to 2 liters of water per day, without waiting for thirst (the sensation of thirst is a sign of an already established deficit). In case of strong heat or physical activity: 3 liters and more. Prefer cool water (not iced).
Cooling down	Spend at least 3 hours a day in a cool place (< 25°C). Regularly mist skin and wrists. Take cool (not cold) showers or baths. Wet a cloth for the neck and temples.
Adapted diet	Favor water-rich foods (cucumber, melon, tomatoes, zucchini). Avoid heavy meals and digestion (which increases internal heat production). Maintain sodium intake through normal diet.
Vulnerable populations	Elderly people (> 65 years old), infants, people on diuretics or neuroleptics, kidney or heart failure patients: medical consultation recommended during heatwaves to adapt treatments and monitoring.
Warning signs	Stop all activity and call 15 (emergency medical service) in case of: persistent temperature > 38.5°C, confusion or disorientation, cessation of sweating despite heat, loss of consciousness or convulsions. These signs indicate heatstroke — an absolute medical emergency.