Coffee: Why This Beverage Can Be Dangerous During a Heat Wave

On June 23, 2026, France logged 336 heat records in a single day, including 131 absolute records, among them 44.3°C in Pissos, Landes — a new regional record for Nouvelle-Aquitaine. These episodes mark a rupture in our daily life and force us to rethink our everyday rituals, from the morning coffee to sleepless nights. Because while health authorities multiply recommendations, one stands out: significantly limit coffee consumption. A seemingly innocent habit that, at temperatures above 40°C (104°F), can become a physiological trap.

An unprecedented summer 2026: when record-breaking becomes the norm

The heat wave that has been battering France since the Thursday before June 23, 2026 has already claimed at least five direct victims: three elderly people in Gironde and two children in Vaucluse. According to Météo-France data, the national thermal index reached 29.8°C at 5 p.m. on June 23, surpassing 29.4°C set in 2003 and 2019, the prior records for the hottest day ever recorded in France. (1)

336 records in a single day: the numbers of extremity

The tally for June 23, 2026 defies belief: 58 departments placed on red heat-alert status, 31 others on orange alert. Temperatures ran 15 to 20 degrees above seasonal norms, with apparent temperatures ranging from 104 to 118°F, especially in the Southwest. Tropical nights followed one another, with nocturnal lows hovering between 73 and 82°F from Wednesday to Thursday. A real lack of genuinely restorative rest.

“Today, hospitals are holding up, and the heatwave has not yet taken a toll on hospital services,” said Stéphanie Rist, France’s Health Minister, on June 23. But the minister already urged continued preventive measures, including staying as sheltered as possible, avoiding outdoor sports in direct sun, and staying well hydrated and nourished. A vigilance that is now extending even to hot beverages.

Why heatwaves are intensifying and lengthening

Daniel Gagnon, a professor at the University of Montreal, explains that “aging, starting around 65, is associated with a reduced ability of the body to shed heat, which can lower tolerance to very high temperatures.” The body then struggles to lose heat through sweating or vasodilation, i.e., the widening of blood vessels in the skin. And caffeine can interfere with these mechanisms.

Coffee isn’t a friend during a heatwave

Public Health France is blunt: “These beverages promote dehydration.” The body can lose up to 1.5 liters of sweat per hour, even without exertion, in periods of strong heat. Caffeine, by activating the kidneys, can intensify this diuretic effect at the worst possible moment. ANSES adds that during heat, caffeine diminishes thermoregulation capabilities, hindering the body’s ability to cool itself properly. (2)

Dr. Gérald Kierzek, an ER physician and medical director at Doctissimo, recommends lowering the EFSA threshold and offsetting each cup of coffee with a large glass of water. The European Food Safety Authority typically sets the daily maximum caffeine dose at 400 mg for a healthy adult. That equates to about 2 espressos or 2.5 cups of brewed coffee. But there is no specific threshold defined for hot periods.

Refreshing alternatives emerging: from the market to culture

In the face of the heat wave, habits are evolving rapidly. In Lot-et-Garonne, ice cream shops are seeing an unprecedented surge of customers. Brandon, an artisanal ice cream maker, says, “We can’t step out without staying hydrated constantly.” His innovation? Basil-lemon sorbets or frappes built on crushed ice. These alternatives attract a clientele seeking cool relief. (3)

Chicory, a durable coffee alternative, is also gaining ground. Caffeine-free, this beverage preserves the ritual of a warm morning drink without compromising hydration. A gentle transition toward habits better suited to extreme summers. (4)

Durable hydration: toward drinks with less impact

Water remains the absolute reference. Public Health France reminds that when we sweat, we lose water and minerals. This can lead to dehydration, especially among vulnerable people. It is therefore essential to drink regularly, even when you don’t feel thirsty.

But the question goes beyond individual health. Coffee production carries a significant carbon footprint, while coffee prices rise under the influence of climate disruption. Rethinking consumption thus becomes a double challenge: health and the environment. (5)