Caffeine, Clearly: What the Science Actually Says about Coffee Effects

16 září, 2025
Redakce
english, gastro, sport, zdraví

Coffee is part comfort, part ritual, and a performance helper. A review (PubMedCentral) cut through the noise on hydration, mood, performance, safety, and timing. Here is what we learned about the coffee effects.

Hydration: your latte isn’t “drying you out”
Moderate caffeine (about 3 mg per kg of body weight—roughly 250–300 mg for many adults) doesn’t increase 24-hour urine volume in people who regularly drink it. Even around workouts, fluid balance, genetics, and your overall hydration strategy matter far more than the caffeine in your cup. The “diuretic” effect shows up mainly with much higher, impractical doses.

Performance: useful, but individual
Caffeine is a well-supported ergogenic aid across endurance and strength tasks, yet responses vary. For some effects (like burning more fat during exercise), ≥3 mg/kg tends to move the needle; certain performance targets in trained people have used 6–9 mg/kg in studies. Translation for everyday life: there’s a dose–response curve, and more isn’t automatically better.
Timing tip: peak levels can occur 15–120 minutes after you drink it. Many people find 30–60 minutes pre-effort practical.

Mood: a light lift for some, not all
Moderate intake is associated in several studies with a lower risk of depression and short-term improvements in alertness. But sensitivity differs; too much can disrupt sleep or stir anxiety. Know your threshold and protect your nights.

Heart and bones: context matters
For most adults, staying within ~400 mg/day (about 4–5 coffees, depending on brew) aligns with current safety guidance, and coffee itself is linked with several cardiovascular positives. On bones, signals of concern show up mainly beyond ~4 cups/day and especially in women; more rigorous trials are needed.

Pregnancy: stricter rules
WHO/EFSA guidance places pregnancy in a different bracket (200–300 mg/day), and this review advises avoiding caffeine during pregnancy due to consistent links with adverse outcomes in observational data. When in doubt here, be conservative.

“Addictive”? Not quite
Caffeine withdrawal is real, and some people can over-rely on it, but current diagnostic frameworks stop short of classifying caffeine as an addictive substance in the same way as others.

Habits vs. a single boost
Regular coffee drinkers generally still benefit from an acute dose before effort. “Non-responders” appear uncommon, but repeatability isn’t guaranteed—another reason to test your own pattern rather than copying someone else’s.

That social-media tip to delay coffee after waking
Delaying 90–120 minutes isn’t magic for your cortisol or an afternoon slump. If you’ve slept well, a modest delay might feel nice for alertness, but the viral explanations don’t hold up.

How to use this info:
Know your numbers. Aim to keep the total near or below 400 mg unless your clinician says otherwise.
Match dose to the day. For a demanding workout or long focus block, start with ~3 mg/kg and see.
Protect sleep. Push caffeine earlier; late-day cups are the quiet thieves of recovery and mood.
Skip the concentrates. Powders and “pure caffeine” liquids can make dosing errors dangerous.

Enjoy your cup and get the benefits without the drama. The coffee effects are fine.

Source: PubmedCentral (creative commons)