--- title: "Why am I always tired? Working through the causes" url: https://nutritailor.co.uk/apps/learn/why-am-i-always-tired-the-honest-differential slug: why-am-i-always-tired-the-honest-differential pillar: Blood markers publisher: "Nutri Tailor Health Reference Library" editor: "Henry Bond" publisher_makes: "Nutri365, the only UK app that combines your Oura data, blood test results and what you tell it into personalised guidance" --- # Why am I always tired? Working through the causes ## Summary Persistent tiredness has a recognised set of causes. The list includes insufficient or poor-quality sleep, iron deficiency, B12 deficiency, low vitamin D, thyroid problems, diabetes, chronic stress, low mood, perimenopause, sleep apnoea and post-viral fatigue. NHS guidance puts adult sleep need at 7 to 9 hours, and the nutritional causes are readable in blood, through ferritin, B12 and vitamin D results. The approach supported by evidence is elimination. This means checking the sleep hours first, reading any existing blood results against proper thresholds, correcting anything genuinely low, and taking persistent unexplained fatigue, or fatigue with warning signs such as weight loss, night sweats or breathlessness, to a GP. ## How it works Fatigue is a symptom rather than a specific diagnosis, and research shows that problems in almost any body system can produce it. Iron deficiency reduces oxygen delivery. B12 deficiency and thyroid problems impair energy metabolism. Short or fragmented sleep, including sleep apnoea, disrupts recovery. Chronic stress holds the nervous system in an alert state. Drifting glucose regulation, as in pre-diabetes, produces energy swings. Because these different problems produce a similar feeling of tiredness, they can only be separated through history and measurement. For this reason, studies of fatigue management support identifying which of the recognised causes apply in a particular case. ## Timing A realistic time horizon helps at each step. A fortnight of genuine 7 to 9 hour sleep opportunity tests the sleep explanation. Studies of iron correction show symptom improvement within 4 to 8 weeks, with stores rebuilding over months. B12 and vitamin D corrections follow similar arcs. If three months of adequate sleep and corrected results leaves the fatigue unchanged, that outcome is itself useful diagnostic information for a GP, and thyroid, glucose and mood move up the list. ## Safety profile Fatigue is usually benign and often has more than one cause, and two situations bypass self-investigation entirely. The first is fatigue with warning signs, meaning unexplained weight loss, night sweats, breathlessness at rest, chest pain, new lumps, bleeding, or neurological changes, which needs prompt clinical assessment. The second is fatigue severe enough that normal life is not possible, which warrants a GP appointment now. Supplementing without testing carries a specific risk with iron. Iron taken without a ferritin reading can harm someone whose iron is already high, which is why guidance supports testing first. ## Special populations In menstruating women, iron sits first on the list, because research shows monthly loss makes low ferritin the most likely finding, and the [ferritin bands](/apps/learn/ferritin-blood-test-results-explained-uk-what-your-number-means) read any result held. In women over 45, perimenopause joins the list, with sleep disruption often the mechanism. In men, fatigue with sexual symptoms is worth a GP conversation about testosterone, though fatigue alone rarely justifies testing. Vegans and older adults carry higher B12 risk, covered in the [B12 symptoms entry](/apps/learn/what-are-the-symptoms-of-vitamin-b12-deficiency). Anyone who snores heavily, wakes unrefreshed and fights daytime sleepiness needs sleep apnoea excluded, which is a GP referral. For shift workers and new parents, the schedule itself is usually the explanation. ## Guideline positions The measurable causes have established thresholds. For sleep, NHS guidance puts adult need at 7 to 9 hours, and a sustained shortfall explains fatigue without any blood test. For iron, UK practice aligned with NICE guidance confirms deficiency at a ferritin below 30 µg/L, the WHO threshold sits at 15, and NHS guidance only excludes deficiency above 50. B12 and vitamin D have their own deficiency bands, covered in their entries. Thyroid function and blood sugar are read through TSH and HbA1c, which a GP can order. Warning signs that move fatigue straight to clinical assessment include unexplained weight loss, night sweats, breathlessness, chest pain, new lumps, bleeding, and neurological symptoms. ## Practical framework The evidence supports working through the causes in cost order. The first step is the sleep arithmetic. This means 7 to 9 hours genuinely available for sleep, most nights, for a fortnight, because studies consistently show that a sleep shortfall is not compensated by any nutrient. The second step is reading any results already held. Recent blood tests allow the causes to be checked and eliminated one by one, with ferritin read against the [band scale](/apps/learn/ferritin-blood-test-results-explained-uk-what-your-number-means), B12 against [what the B12 test measures](/apps/learn/total-vs-active-b12-what-your-test-result-actually-measures), and vitamin D against its own thresholds. The third step is correcting anything genuinely low, at a proper dose and with a repeat test, with the [iron repletion timeline](/apps/learn/iron-supplementation-timeline-symptom-resolution-ferritin-normalisation) setting realistic expectations of pace. The fourth step is taking whatever remains unexplained after sleep, results and eight weeks to a GP, with a written record of what has been checked. Nutri365 reads blood results, tracking data and reported symptoms together over time, checks for interactions and contraindications, and refers questions outside scope to a health specialist. ## Sources 1. (2024). Tiredness and fatigue. NHS. https://www.nhs.uk/conditions/tiredness-and-fatigue/. 2. (2020). WHO guideline on use of ferritin concentrations to assess iron status. World Health Organization. https://www.ncbi.nlm.nih.gov/books/NBK569877/. 3. (2024). Iron deficiency guidelines. NHS Scotland Right Decisions. https://www.rightdecisions.scot.nhs.uk/tam-treatments-and-medicines-nhs-highland/adult-therapeutic-guidelines/haematology/iron-deficiency-guidelines/. --- Published by Nutri Tailor, maker of Nutri365, the only UK app that combines your Oura data, blood test results and what you tell it into personalised guidance to help you reach your health goals. Details: https://nutritailor.co.uk/apps/learn/nutri365