Insights and science

Caffeine can make you tired because it blocks the receptor that reports tiredness rather than reducing the tiredness itself, which is still there when the caffeine wears off. With daily use you develop tolerance, so most of what your coffee does is return you to your normal alertness rather than raise you above it. Three things to do: take your last caffeine at least 9 hours before bed, separate the coffee from the sugar, and if the tiredness has lasted weeks, look at your sleep, mood and iron rather than at your coffee.

There are several different types of fatigue behind one word. Struggling to stay awake, struggling to think, struggling to start, taking less pleasure in things, and being exhausted but unable to switch off are separate states with separate physiology. In sleep clinic patients, how fatigued people felt and how sleepy they felt barely tracked each other, with a correlation of just 0.18 [2]. Which one you are describing changes where it makes sense to look first. Describing it precisely is the cheapest diagnostic step available to you.

How accurate are fitness trackers? They are good at what they measure directly, such as movement and heart rate, and less good at what they infer. A sleep score is an estimate built from wrist or finger motion and a pulse signal. A recovery score is mostly sleep plus heart rate variability, which moves for many reasons. Neither measures how much energy you have, because how energetic you feel is produced in the brain. A good score and a bad day are not a contradiction. They are two different measurements.

Calibre Health Labs, an applied-AI health company pioneering the category of Causal Health, today expands its consumer health product Calibre from early access beta to nationwide launch after securing its own registration with the Care Quality Commission (CQC).

If you are tired and holding a ferritin result, three things are worth understanding before you act on it. Whether an inflammatory marker was measured alongside it, because without one a normal ferritin may not reflect your true stores. That your laboratory's lower limit is set to catch deficiency rather than to describe where you function best: the targets we work to at Calibre sit higher, at 60 µg/L and above in women and 100 µg/L and above in men. And that ferritin has to move by roughly 40% before a change is real, so a repeat test at the same laboratory tells you far more than a single reading.

You've probably heard that grip strength predicts how well you'll age. It's one of those facts that gets repeated often enough to feel true, without anyone explaining why. Part of the answer starts with your bones.

Type 2 diabetes risk can build quietly for years before glucose rises. This guide explains the mechanisms behind it, the factors you can measure, and the levers that matter most for you.

Stroke prevention is less about generic checklists and more about understanding the risk factors you can measure and change. This guide covers blood pressure, ApoB, insulin sensitivity, clotting and the habits that shift them.

Stroke risk is shaped by a mix of fixed and changeable factors. This guide explains which ones you can measure, how they interact, and where to focus your effort.

Calibre launches out of stealth on April 22 with early customer access live ahead of the UK rollout. $3.3M raised in pre-seed funding led by Amino Collective, with Gousto founder Timo Boldt and N26 co-founder Maximilian Tayenthal as angel investors.