Why Am I Always Tired? 7 Nutrient Deficiencies That Drain Your Energy
Intro (hook + set expectations, ~100 words):
You’re sleeping roughly the same hours as always, you’re not obviously ill, and yet by mid-afternoon you’re running on fumes. It’s one of the most common things people search for — and one of the most frustrating, because “just tired” can come from dozens of directions: stress, poor sleep quality, thyroid issues, or something as basic as a nutrient gap that’s built up quietly over months.
This isn’t a diagnosis list — persistent fatigue is always worth mentioning to your GP, especially if it’s new, severe, or paired with other symptoms. But several well-documented nutrient shortfalls are strongly linked to low energy, and they’re worth understanding before you assume it’s “just life.”
1. Iron Deficiency
Iron carries oxygen around your body via haemoglobin — when levels drop, your tissues (including your brain and muscles) are quite literally running on less oxygen, which shows up as fatigue, breathlessness on exertion, and difficulty concentrating. It’s the most common nutrient deficiency in the UK, particularly among women with heavy periods, and it develops gradually enough that many people adjust to feeling tired without realising it’s not “normal.”
→ Full guide: Iron Deficiency Symptoms, Causes & Sources
2. Vitamin B12 Deficiency
B12 is essential for red blood cell formation and nervous system function, and because it’s stored in the liver for years, deficiency tends to creep up slowly rather than hit suddenly. It’s a near-universal risk for vegans (B12 is found almost exclusively in animal products) and becomes more common with age, since stomach acid — needed to absorb B12 from food — naturally declines over time.
→ Full guide: Vitamin B12 Deficiency Symptoms & Who’s at Risk
3. Vitamin D Deficiency
Vitamin D contributes to normal immune function and normal muscle function — both of which are commonly reported as “off” when levels are low. Given the UK and Northern Europe’s limited winter sunlight, a large share of adults run low without realising it, particularly anyone spending most daylight hours indoors.
→ Full guide: Vitamin D Deficiency Symptoms & Sources
4. Magnesium Deficiency
Magnesium is directly linked, via an EFSA-authorised health claim, to the reduction of tiredness and fatigue — one of the few nutrients with that specific wording approved. It’s involved in energy metabolism at a cellular level, and low intake is thought to be common given how much modern diets rely on processed food.
→ Full guide: Magnesium Deficiency: Signs, Causes & Sources
5. CoQ10 Decline
Unlike the nutrients above, CoQ10 isn’t something you can be “deficient” in in the classic sense — your body makes its own supply. But that production naturally declines from your mid-30s onward, and more sharply if you take statins. Since CoQ10 plays a central role in how your cells generate energy, this decline is one plausible (though not fully proven) contributor to age-related fatigue.
→ Full guide: CoQ10 Benefits for Energy: What the Science Says
6. Poor Sleep Quality (Not Just Sleep Quantity)
Worth naming explicitly: seven or eight hours of poor sleep isn’t the same as seven or eight hours of good sleep. Fragmented sleep, late screen use, alcohol close to bedtime, or an inconsistent sleep schedule can all leave you feeling under-slept even when the hours technically add up. This isn’t a nutrient issue, but it’s often tangled up with one — magnesium, for instance, is commonly discussed in relation to sleep quality.
7. Thyroid Function
An underactive thyroid (hypothyroidism) is a genuine medical cause of persistent fatigue, and it’s often missed because its symptoms (tiredness, weight gain, feeling cold, low mood) overlap so heavily with nutrient deficiencies. It’s diagnosed with a simple blood test — if fatigue persists despite addressing diet, sleep, and the nutrients above, this is worth raising with your GP directly.
So What Should You Actually Do?
Guessing which of these applies to you — and supplementing broadly “just in case” — isn’t a great strategy; some of these nutrients (iron especially) can cause harm if taken without an actual deficiency. The more useful approach:
- Look at your specific pattern. Fatigue paired with breathlessness points differently than fatigue paired with poor sleep or frequent colds.
- Consider a GP blood test if fatigue is persistent, severe, or unexplained — this is the only way to confirm iron, B12, or thyroid issues rather than guess.
- Use diet and lifestyle as your first lever — the nutrient guides linked above each cover food sources specific to that nutrient.
- Get a personalised starting point. Our free AI analysis looks at your diet, sleep, activity, and specific concerns together, rather than asking you to self-diagnose from a list.
FAQ
Can dehydration cause fatigue? Yes — even mild dehydration is a well-documented cause of tiredness and reduced concentration. It’s worth ruling out before assuming a nutrient gap: aim for pale-yellow urine as a rough hydration marker.
How long does it take to feel better after fixing a deficiency? This varies by nutrient and by how depleted you were to start. Some people notice a difference in energy within a couple of weeks of consistent supplementation or dietary change; iron and B12 in particular can take longer, since the body needs time to rebuild stores.
Should I just take a multivitamin to cover all of these? A general multivitamin can help fill small gaps, but the doses are often too low to meaningfully correct an existing deficiency (magnesium and iron are common examples of “underdosed” nutrients in multivitamins). If you suspect a specific deficiency, a targeted supplement — ideally alongside a blood test — is usually more effective than a broad multivitamin.
Is it normal to feel tired all the time? Occasional tiredness is normal. Persistent, unexplained fatigue that doesn’t improve with rest is not something to just accept — it’s worth investigating, whether the cause turns out to be nutritional, related to sleep, or something that needs a GP’s input.
Sources & Further Reading
- NHS — Self-help tips to fight tiredness
- NHS — Underactive thyroid (hypothyroidism)
- NIH Office of Dietary Supplements — Iron, Vitamin B12, Magnesium
- EFSA — Authorised health claims register
- Examine.com — Fatigue and micronutrients
This article is for general educational purposes only and is not medical advice. If fatigue is persistent, severe, or accompanied by other symptoms, please speak with your GP.