Drinking copious iced coffee to quench thirst on hot days?

I drink one cup of coffee daily. During hot weather, I increase it to two or three cups, often with a lot of ice, wondering if this can replace filtered water? (Hoang, 29, Hanoi).

Coffee primarily contains caffeine. An average 150ml cup of Vietnamese filter coffee typically contains about 90-120mg of caffeine. Consuming coffee can enhance alertness, improve focus, temporarily boost work performance, and elevate mood.

However, caffeine consumption can also lead to dehydration due to its mild diuretic effect, which increases water excretion through the kidneys. In hot weather, over-relying on coffee can worsen dehydration. This may result in dizziness, fatigue, or even heatstroke if adequate fluids are not replenished.

During hot days, proper timing and consumption methods are crucial. It is advisable to drink coffee at least one to two hours after breakfast. The ideal window is between 8:30 a.m. and 10:30 a.m., when blood cortisol levels—a natural alertness-boosting hormone—begin to decline, thereby maximizing coffee's stimulating effect.

Experts recommend limiting daily coffee intake to about one cup, not exceeding 200-300mg of caffeine. When consuming coffee, it is essential to drink plenty of water alongside it. Avoid drinking coffee on an empty stomach or during strenuous outdoor activities. Furthermore, refrain from coffee if experiencing signs of dehydration, such as headaches or dizziness.

Individuals with heart rhythm disorders, high blood pressure, or a history of anxiety and insomnia should limit their coffee consumption. The elderly, pregnant women, children, and those working outdoors in hot weather should avoid excessive caffeine intake due to increased sensitivity or risk.