Chronic fatigue: five causes and what fixes each

Last reviewed: 7 May 2026

"I'm always tired" is one of the most common complaints in modern UK life, and one of the least useful diagnoses. Tiredness isn't a condition — it's a symptom with several very different causes, each needing a different response. Treating all fatigue the same is why a lot of people try supplement after supplement without results.

The difference between tired and chronic tired

Normal tiredness is what you feel after a hard week, a short night, a flu, a big workout. It lifts with rest. Chronic tiredness is different — it persists through weekends off, full nights of sleep, and time away. It interferes with work, mood, exercise and relationships. If your tiredness is in this second category, one of the following five causes is almost always at work.

Cause 1: You are genuinely not sleeping enough

Obvious, but easily missed. Adult UK sleep averages have drifted down for two decades, and the honest baseline is that most adults need 7–9 hours of actual sleep (not time in bed) most nights to function at their best.

The signs: you fall asleep within minutes of hitting the pillow, sleep through alarms, feel foggy in the mornings, need caffeine to function before 11 am, catch up on weekends.

The fix: add 30–60 minutes to your sleep window and hold it for three weeks. Prioritise consistent wake time over weekend lie-ins. Address scroll-time-in-bed. For more structure, our sleep guide covers the practical playbook. NICE CKS guidance on insomnia stresses sleep hygiene and CBT-I as first-line non-pharmacological options.^[1]

Magnesium supports normal function of the nervous system (authorised claim) and some people notice that it helps them fall asleep and stay asleep. An 8-week RCT in older adults with primary insomnia found 500 mg/day magnesium improved sleep efficiency, sleep onset and Insomnia Severity Index vs placebo.^[2] Our MagActive delivers 300 mg across four organic forms.

Cause 2: Chronic stress and cortisol dysregulation

Stress itself does not make you tired — but chronic, prolonged stress exhausts the HPA axis (the hypothalamic-pituitary-adrenal system that regulates cortisol). High cortisol at the wrong times, flattened cortisol curves, or chronically elevated baselines all produce the "wired and tired" pattern that is so common in high-responsibility roles.

The signs: you feel tired but struggle to fall asleep. You wake at 3 am and cannot settle. You feel "on" even when exhausted. Stress-eating and sugar cravings spike in the afternoon.

The fix: this one requires addressing the stress itself — workload, relationships, lifestyle pattern — and supporting the physiology around it. Our stress management guide covers the full playbook.

On the supplement side, a 60-day RCT of standardised KSM-66 ashwagandha (300 mg twice daily) showed significant reductions in serum cortisol and self-reported stress vs placebo.^[3] Our Ashwagandha KSM-66 uses the standardised extract referenced in that research.

Cause 3: Nutritional gaps

Specific nutrient deficiencies produce specific tiredness patterns. The most common in UK adults:

Iron deficiency — especially in women with heavy periods, vegetarians, vegans, and endurance athletes. Shows up as pale complexion, breathlessness climbing stairs, cold hands and feet, hair shedding. Needs a blood test and iron supplementation under GP guidance rather than casual self-treatment (too much iron is its own problem).^[4]
Vitamin B12 deficiency — common in vegans and vegetarians, and in older adults whose absorption has reduced. A 2014 review of B12 status in vegetarians and vegans documented high rates of deficiency, particularly among long-term vegans, infants and pregnant women.^[5] Shows up as fatigue plus neurological signs (pins and needles, mood changes). Also needs a blood test.
Vitamin D deficiency — almost universal in UK adults through winter; SACN recommends 10 µg/day from October to March.^[6] Vitamin D contributes to normal function of the immune system and to normal muscle function (authorised claims). Our D3+K2 covers this year-round.
Magnesium shortfall — common when diet is high in processed food. Contributes to normal muscle function, normal psychological function, and reduction of tiredness and fatigue (authorised claims).^[7]
B-vitamin shortfall — thiamine (B1), riboflavin (B2), niacin (B3), B6, B12 and folate all contribute to normal energy-yielding metabolism (authorised claim). Pantothenic acid (B5) contributes to normal mental performance (authorised claim). Our B-Complex covers all 8 B-vitamins in methylated or active forms.

The fix: if suspected, test with your GP. Don't stack high-dose single nutrients without knowing whether you need them. A sensible B-complex, vitamin D, and omega-3 covers most of the nutritional gap territory for UK adults with varied diets.

Cause 4: Hidden medical causes

Chronic tiredness that persists despite good sleep, reasonable nutrition and sensible stress management is a legitimate reason to see a GP. Several conditions present primarily as "I'm always tired" and are overlooked in people who self-diagnose:

Anaemia (iron, B12 or folate).
Underactive thyroid — more common than many realise, especially in women over 40.
Type 2 diabetes — early stages present as fatigue, thirst, frequent urination.
Sleep apnoea — loud snoring, daytime sleepiness, waking unrefreshed.
Depression — "anhedonic fatigue" rather than classic sadness.
Coeliac disease — surprisingly common, presents with fatigue and vague digestive symptoms.

A standard blood panel (full blood count, ferritin, thyroid function, B12, folate, vitamin D, HbA1c) costs your GP nothing and resolves most of this list. This is the single most underused move in chronic-fatigue self-management.

Cause 5: Lifestyle misalignment

Sometimes none of the above. Sometimes the cause is that the shape of your life doesn't match what your body needs. A role that demands 12-hour days indefinitely. A relationship that drains more than it nourishes. A commute that consumes the hours that would otherwise be recovery time. A training volume that outstrips recovery capacity.

The fix: no supplement fixes this. The changes required are structural — the hours you work, the obligations you take on, the amount of time you spend recovering versus performing. Adaptogens and B-complex make the transition more bearable, but they do not replace rest that the body needs and isn't getting.

Where supplements genuinely fit across the five causes

B-Complex — the single most useful supplement for the "tired-because-diet-is-inconsistent" case. Covers all 8 B-vitamins with multiple authorised energy and psychological claims.
Vitamin D — the UK winter fatigue case.
Magnesium — the sleep-and-muscle-tension case.
Ashwagandha — the chronic-stress-and-wired-tired case.
Iron — only with GP guidance and confirmed deficiency.
Omega-3 — not fatigue-specific but part of the broader nutritional baseline.

Stacking these four (B-complex, vitamin D, magnesium, ashwagandha) covers most non-medical fatigue territory for UK adults.

A sensible order of operations

Check sleep honestly. Actual hours of sleep, not hours in bed. Address if low.
Check stress pattern. Wired-and-tired vs genuinely depleted.
Get a blood panel if fatigue has persisted more than a few weeks.
Tighten nutritional baseline — B-complex, vitamin D (winter), omega-3, magnesium.
Add ashwagandha if the stress side is clearly present.
Make structural lifestyle changes if the root is in the shape of your life.
See your GP if fatigue persists despite 1–6 and blood results were normal — there may be something less common going on.

In practice

"Being tired" is rarely one thing. In most adults, it is some mix of under-sleeping, chronic stress, small nutritional gaps, and a lifestyle that keeps the body permanently in "output" mode. Rest, food, sleep and stress management address most of it. B-complex, vitamin D, magnesium and ashwagandha cover the highest-ROI supplementation. The medical route catches the cases that look like fatigue but are something else. The expensive "anti-fatigue" formulas sold online rarely outperform this basic framework for anyone who actually implements it.

References

NICE Clinical Knowledge Summaries. Insomnia. cks.nice.org.uk
Abbasi B, Kimiagar M, Sadeghniiat K, et al. The effect of magnesium supplementation on primary insomnia in elderly: A double-blind placebo-controlled clinical trial. J Res Med Sci. 2012;17(12):1161–1169. PubMed: 23853635
Chandrasekhar K, Kapoor J, Anishetty S. A prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of ashwagandha root in reducing stress and anxiety in adults. Indian J Psychol Med. 2012;34(3):255–262. PubMed: 23439798
NHS. Iron. nhs.uk
Pawlak R, Parrott SJ, Raj S, Cullum-Dugan D, Lucus D. How prevalent is vitamin B(12) deficiency among vegetarians? Eur J Clin Nutr. 2014;68(5):541–548. PubMed: 24667752
Scientific Advisory Committee on Nutrition. SACN Vitamin D and Health Report (2016). gov.uk
European Commission. EU Register of Nutrition and Health Claims Made on Foods. ec.europa.eu