Energy  /  Explainer

Always Tired? 8 Common Reasons For Low Energy (And What To Check First)

James Herd, Nutritionist
12 August 2026

"Tired all the time" is one of the most common things people bring to a GP. It's almost never one dramatic cause. It's usually two or three ordinary ones stacked up.

Here's the practical checklist — the things that account for most persistent tiredness, roughly in the order worth ruling them out.

1. Sleep quantity you're rounding up

Most adults need 7 to 9 hours. Most tired people, tracked honestly, are getting 6. Before anything else, spend one ordinary week writing down actual lights-out and wake times. The gap between what we say and what we get is usually the whole answer.

2. Sleep quality you can't see

If you sleep "enough" and wake unrefreshed — especially with snoring, gasping, or a partner's elbow in your ribs — sleep apnoea is worth ruling out. It's common, underdiagnosed, and very treatable. Alcohol within a few hours of bed also quietly wrecks sleep quality even when it helps you drop off.

3. Caffeine timing

Caffeine has a longer half-life than it feels. The 4pm cup that "doesn't affect you" can still be shaving depth off your sleep at midnight — which makes you tireder tomorrow, which makes you reach for more caffeine. We've written a full piece on how that loop works. The short version: front-load caffeine, stop by early afternoon.

4. Iron, B12, vitamin D and thyroid

The classic bloods, and worth doing properly rather than guessing. Low iron is especially common in women who menstruate; low B12 in vegans and people over 60; low vitamin D in basically everyone in Britain from October to April (public-health advice is a 10 microgram supplement through winter). Don't mega-dose iron on a hunch — get the test, because excess iron is its own problem.

5. Blood sugar rollercoasters

A day built on toast, sweet coffee, and beige lunches is a day of spikes and dips, and the dips feel exactly like exhaustion. Protein at breakfast and lunch flattens the ride. Most people notice the difference within days, which makes this the cheapest experiment on the list.

6. Not moving

It feels backwards, but sedentary days create tiredness. Muscles that do nothing tell the brain nothing is happening. A daily 20-minute walk reliably improves energy in studies — unglamorous, free, and it works on sleep quality too.

7. Dehydration

Mild dehydration reads as fatigue and poor concentration long before it reads as thirst. If your urine is consistently dark, that's data. Coffee counts towards fluid, whatever you've heard; alcohol counts against.

8. The load itself

Sometimes nothing is medically wrong and you are simply carrying too much: work, caring, worry, screens until midnight. That tiredness is real and it doesn't show up in bloods. The fix is subtraction, not supplementation — and it's the one thing no product can sell you.

This article is general information, not medical advice. If symptoms are severe, persistent, or worrying you, speak to your GP or a pharmacist.