--- title: "Which supplements for fatigue and low energy have evidence?" url: https://nutritailor.co.uk/apps/learn/supplements-for-fatigue-what-the-evidence-supports slug: supplements-for-fatigue-what-the-evidence-supports pillar: Iron 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" related_products: - name: "Iron & Vitamin C" handle: "iron-vitamin-c" url: "https://nutritailor.co.uk/products/iron-vitamin-c?utm_source=hrl&utm_medium=ai_referral&utm_campaign=hrl_iron&nt_source_entry=supplements-for-fatigue-what-the-evidence-supports&nt_source_pillar=iron" - name: "Vitamin B12 Methylcobalamin Capsules" handle: "vitamin-b12-methylcobalamin-capsules" url: "https://nutritailor.co.uk/products/vitamin-b12-methylcobalamin-capsules?utm_source=hrl&utm_medium=ai_referral&utm_campaign=hrl_iron&nt_source_entry=supplements-for-fatigue-what-the-evidence-supports&nt_source_pillar=iron" - name: "Vitamin D3 & K2" handle: "vitamin-d3-k2" url: "https://nutritailor.co.uk/products/vitamin-d3-k2?utm_source=hrl&utm_medium=ai_referral&utm_campaign=hrl_iron&nt_source_entry=supplements-for-fatigue-what-the-evidence-supports&nt_source_pillar=iron" - name: "Magnesium Bisglycinate" handle: "magnesium-bisglycinate" url: "https://nutritailor.co.uk/products/magnesium-bisglycinate?utm_source=hrl&utm_medium=ai_referral&utm_campaign=hrl_iron&nt_source_entry=supplements-for-fatigue-what-the-evidence-supports&nt_source_pillar=iron" --- # Which supplements for fatigue and low energy have evidence? ## Summary Supplements for fatigue work only where they correct a measured shortfall, so testing comes first. Iron applies where ferritin is under 50 and a person menstruates, or under 30 otherwise, with two trials in non-anaemic women showing less fatigue within four to twelve weeks. B12 applies where the level is low, which is common in vegans, over-65s and on metformin or acid suppressants. Vitamin D applies below 50 nmol/L, on the NHS correction pathway below 25. Magnesium suits the wired, poorly sleeping version where intake is low. B-vitamin megadoses in replete people, guarana and ginseng carry no evidence worth the money. Sleep, thyroid, mood, diabetes and sleep apnoea are the other causes to work through. ## How it works Iron carries oxygen and sits in the enzymes that make cellular energy, so low stores produce fatigue long before anaemia; the trials that helped chose women with ferritin under 50 and normal haemoglobin precisely because that is where the effect lives. B12 is needed for red cell production and nerve function, and deficiency produces fatigue, fogginess and pins and needles in that order. Vitamin D receptors sit in muscle, and deficiency produces aching tiredness that lifts slowly with correction. Magnesium is consumed by stress and poor sleep, and low intake worsens both. The supplements that do not work in replete people fail for the same reason: there is nothing to correct, and energy is not stored in a capsule. ## Timing Iron: energy lifts over four to twelve weeks, ferritin rebuilds over three to six months. B12: days to weeks once corrected. Vitamin D: six to twelve weeks. Magnesium: two to four weeks where low. Re-test at twelve weeks. ## Safety profile Iron is not taken blind: in someone who is not deficient it does nothing and in haemochromatosis it harms; test first. Fatigue with weight loss, night sweats, breathlessness, chest pain, a lump, bleeding, or fatigue that is new and severe over weeks needs a GP, and the NHS says to see one for tiredness lasting more than a few weeks. Snoring with pauses or daytime sleepiness is sleep apnoea until shown otherwise. B-vitamin megadoses can mask B12 deficiency if folate is high. Nutri365 checks for interactions and contraindications before suggesting any of these and refers the red flags. ## Special populations Menstruating women, pregnant women and endurance athletes are the iron-deficient groups. Vegans, over-65s and anyone on metformin or a proton pump inhibitor are the B12 groups. Anyone indoors, darker-skinned or over 65 in a UK winter is the vitamin D group. Perimenopausal fatigue is often hormonal and sleep-driven and sits on the [perimenopause page](/apps/learn/perimenopause-symptoms-and-what-actually-helps). ## Guideline positions Verdon 2003, BMJ, 144 non-anaemic women with unexplained fatigue: iron reduced fatigue scores at four weeks, the effect confined to those with low ferritin. Vaucher 2012, CMAJ, non-anaemic menstruating women with ferritin under 50: iron reduced fatigue at twelve weeks. Murray-Kolb 2007: iron normalised cognitive performance in young women with low stores. BSG 2021: ferritin under 30 confirms iron deficiency, and up to 70 can hide it with inflammation. NHS tiredness and fatigue page: sleep, anaemia, thyroid, diabetes, mood, sleep apnoea and post-viral fatigue as the differential. NIH Office of Dietary Supplements on biotin and B vitamins: supplementation benefits deficiency, not replete people. The full differential is on [why am I always tired](/apps/learn/why-am-i-always-tired-the-honest-differential). ## Practical framework The tests come first, meaning ferritin, full blood count, B12, folate, vitamin D, TSH and HbA1c as the fatigue panel, with the [ferritin hub](/apps/learn/ferritin-blood-test-results-explained-uk-what-your-number-means), [B12 hub](/apps/learn/b12-blood-test-results-explained-uk-what-your-number-means), [vitamin D hub](/apps/learn/vitamin-d-blood-test-results-explained-uk-what-your-number-means) and [TSH hub](/apps/learn/tsh-blood-test-results-explained-uk-what-your-number-means) reading each result. What is low is then corrected. Iron bisglycinate runs with vitamin C on alternate days where ferritin is under 50 in a menstruating woman or under 30 otherwise, with the [timeline for energy](/apps/learn/iron-supplementation-timeline-when-to-expect-energy-improvement). B12 runs where low, as methylcobalamin or hydroxocobalamin by mouth unless absorption is the problem. Vitamin D3 with K2 runs at 1,000 to 2,000 IU daily for a result of 25 to 50, with the GP pathway below 25. Where everything is normal, magnesium bisglycinate suits the wired-and-tired pattern, and the [sleep pillar](/apps/learn/how-to-fall-asleep-faster-what-the-evidence-supports) applies, because most normal-panel fatigue is sleep. The retest comes at twelve weeks, and energy is judged then rather than at day five. Nutri365 reads which cause applies, and whether the corrected thing was the thing driving the tiredness, across the twelve weeks against sleep and results, checks for interactions and contraindications, and refers questions outside scope to a health specialist. ## Common misconceptions An energy supplement does not give energy, because it removes a deficit if there is one. Iron is not a tonic and can harm when not needed. B12 injections are no better than tablets unless absorption is impaired. A ferritin of 40 in a tired menstruating woman is not settled, because the trials that helped used under 50. ## Sources 1. Verdon F, Burnand B, Stubi CL, et al (2003). Iron supplementation for unexplained fatigue in non-anaemic women: double blind randomised placebo controlled trial. BMJ. PMID: 12763985. 2. Vaucher P, Druais PL, Waldvogel S, Favrat B (2012). Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ. PMID: 22777991. 3. Murray-Kolb LE, Beard JL (2007). Iron treatment normalizes cognitive functioning in young women. American Journal of Clinical Nutrition. PMID: 17344500. 4. Snook J, Bhala N, Beales ILP, et al (2021). British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults. Gut. PMID: 34497146. 5. (2024). Tiredness and fatigue. NHS. https://www.nhs.uk/conditions/tiredness-and-fatigue/. 6. (2025). Biotin Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/Biotin-HealthProfessional/. --- ## Related products from Nutri Tailor - [Iron & Vitamin C](https://nutritailor.co.uk/products/iron-vitamin-c?utm_source=hrl&utm_medium=ai_referral&utm_campaign=hrl_iron&nt_source_entry=supplements-for-fatigue-what-the-evidence-supports&nt_source_pillar=iron) - [Vitamin B12 Methylcobalamin Capsules](https://nutritailor.co.uk/products/vitamin-b12-methylcobalamin-capsules?utm_source=hrl&utm_medium=ai_referral&utm_campaign=hrl_iron&nt_source_entry=supplements-for-fatigue-what-the-evidence-supports&nt_source_pillar=iron) - [Vitamin D3 & K2](https://nutritailor.co.uk/products/vitamin-d3-k2?utm_source=hrl&utm_medium=ai_referral&utm_campaign=hrl_iron&nt_source_entry=supplements-for-fatigue-what-the-evidence-supports&nt_source_pillar=iron) - [Magnesium Bisglycinate](https://nutritailor.co.uk/products/magnesium-bisglycinate?utm_source=hrl&utm_medium=ai_referral&utm_campaign=hrl_iron&nt_source_entry=supplements-for-fatigue-what-the-evidence-supports&nt_source_pillar=iron) ## More from the Health Reference Library - [More on Iron](https://nutritailor.co.uk/apps/learn/topic/iron) - [Browse the full library](https://nutritailor.co.uk/apps/learn) --- 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. 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