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Vitamins for Energy and Tiredness: What Science Says

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The OneVit Team

The OneVit Team

Updated on

22nd May 2026

reading time

12 min

Vitamins for Energy and Tiredness: What Science Says

Feeling tired most of the time is a very common health complaint. But not all tiredness has the same cause, and not all vitamins and supplements for energy or tiredness work in the same way. Some nutrients play a direct role in how your body produces and uses energy. Others only matter when your levels are running low. This guide breaks down what the evidence shows, who benefits most from supplementation, and what to look for in a supplement worth taking.

Why does tiredness happen in the first place?

Before reaching for a supplement, it helps to understand what kind of tiredness you're dealing with. Tiredness is a symptom, not a condition. For some people it's lifestyle-driven: poor sleep, irregular meals, high stress, and not drinking enough water can all add up over the course of a week. For others, persistent low energy points to a nutritional gap, where one or more of the nutrients your body relies on to convert food into energy is in shorter supply than it should be.

The distinction matters because supplements work best when a deficiency is part of the problem. If your tiredness is coming from chronic sleep deprivation or an underlying health condition, no vitamin will fix that. But where nutritional shortfalls are involved, and in the UK they're more common than most people realise, targeted supplementation can make a measurable difference to how you feel day-to-day.

One caveat to flag early: if your tiredness is persistent, unexplained, or coming alongside other symptoms like breathlessness, palpitations, or numbness, see your GP. A blood test can identify deficiencies in iron, B12, folate, and vitamin D, giving you a clearer basis to work from.

B vitamins and energy: what do they actually do?

B vitamins are involved in turning food into energy at a cellular level, and the evidence base for this is well-established. Several members of the B vitamin family, including B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6, and B12, contribute to normal energy-yielding metabolism.1 Niacin, vitamin B6, and B12 also help reduce tiredness and fatigue.2

In practical terms, B vitamins are most useful when your intake is consistently falling short. If you're prone to skipping meals regularly, follow a restrictive diet, or eat a lot of processed food, you're more likely to be operating on a lower B vitamin baseline. They're not stimulants, so don't expect a noticeable energy surge if your levels are already adequate. Think of them as supporting the engine rather than pressing the accelerator.

The reason they're often discussed together is that the B vitamins work as a team. Each one plays a role in the reactions that convert carbohydrates, fats, and proteins into the form of energy your cells actually run on. B6 helps metabolise amino acids. B12 is needed for red blood cell formation, which has a knock-on effect on oxygen delivery. Folate works alongside B12 in DNA synthesis and cell division. The interdependence is the point - a comprehensive review in Nutrients concluded that being low in any one B vitamin means the whole system works less efficiently, since the vitamins rarely act in isolation.3,4

B complex supplements, which contain all eight B vitamins in a single formula, are the most practical approach. OneVit B Complex provides the full spectrum of B vitamins at evidence-informed levels, including B6, B12, niacin, and folate.

Iron: one of the most common nutritional causes of tiredness

Iron is one of the most common nutritional causes of persistent tiredness, particularly in women of reproductive age. Iron contributes to normal energy-yielding metabolism, to oxygen transport in the body, and to the reduction of tiredness and fatigue.2

The reason is straightforward. Iron is essential for producing haemoglobin, the protein in red blood cells that carries oxygen to your muscles, brain, and the rest of your tissues. When iron levels drop, less oxygen reaches where it needs to go, and the result is often a heavy, persistent fatigue that doesn't lift with rest alone. People with iron-deficiency anaemia frequently describe it as a different kind of tiredness, less "I've had a long day" and more "I'm running on empty no matter what I do".

In the UK, iron deficiency is common in women who menstruate heavily, in people who follow plant-based diets (where iron from food is less readily absorbed), and in endurance athletes.5,6 A 2024 analysis of National Diet and Nutrition Survey data found that among UK women of reproductive age, iron deficiency prevalence was around 20%, rising to nearly 50% when a higher threshold was defined.7 The non-haem iron in plant foods (the type found in vegetables, legumes, and grains) is absorbed less efficiently than the haem iron in meat (the type the body absorbs more easily), which is why supplementation is especially relevant for anyone on a vegan or vegetarian diet.

Taking iron when you don't need it offers no benefit, and can cause side effects including constipation and nausea, so it's best to find out exactly what your levels are before starting to take it. If you're supplementing iron, taking it alongside some vitamin C significantly improves how much your body absorbs. A clinical study found that roughly 50mg of vitamin C alongside a meal meaningfully increases iron absorption.8

OneVit Iron is formulated with ferrous bisglycinate, a chelated form of iron. Studies suggest the body absorbs significantly more iron from bisglycinate than from standard ferrous sulphate (90.9% vs 26.7% in one trial), and it was also linked to lower rates of digestive side effects.9

Does vitamin D affect energy levels?

Vitamin D doesn't have a direct role the way B vitamins and iron do, so it's worth being clear on what it can and can't do. Vitamin D contributes to muscle function, and persistent low levels are associated with muscle weakness and a general sense of fatigue.2 Research published in 2023 found that vitamin D supplementation was associated with a measurable reduction in fatigue scores compared with placebo, with the biggest difference in people who were already low in vitamin D.10

What makes vitamin D particularly relevant in the UK is how widespread deficiency is - roughly 1 in 5 UK adults are vitamin D deficient.11 The reason is geographical. The UK sits at a latitude where, from October to March, sunlight is too weak for the skin to make meaningful amounts of vitamin D, regardless of how much time you spend outside. This is why the NHS recommends all UK adults consider a 10mcg daily vitamin D supplement through autumn and winter.12

Correcting a vitamin D deficiency won't deliver an overnight energy boost. But addressing a persistent shortfall, especially over the colder months when your body is doing the most work to keep itself running, can help you feel less physically drained over time. OneVit Vitamin D3 & K2 provides vitamin D3 alongside vitamin K2, which works in tandem with D3 to support how calcium is used in the body.

Vitamin B12: why it matters for energy, especially on a plant-based diet

Vitamin B12 deficiency can develop slowly, is commonly under-recognised, and is significantly more prevalent in certain groups. B12 is also involved in the body's process that converts nutrients into energy your cells can use, as well as the reduction of tiredness and fatigue.2 It's also essential for red blood cell formation and nerve function. When B12 runs low for a sustained period, it can lead to a type of anaemia where red blood cells can't do their job properly, making the tiredness worse on top of the deficiency itself.13

The issue with B12 is that it's found almost exclusively in animal-sourced foods. Meat, fish, eggs, and dairy are reliable ways to get B12, so people following a vegan or vegetarian diet are missing out on key sources. The Vegan Society recommends that vegans supplement with at least 10mcg of B12 daily, or 2,000mcg weekly, to help prevent deficiency.16 This isn't supplementation going above and beyond, it's filling a gap that diet alone can't cover.

OneVit Vitamin B12 uses methylcobalamin, a readily absorbed form, at a daily dose appropriate for ongoing support. It's also included in OneVit B Complex if you'd prefer the full B vitamin range in a single capsule.

Is a multivitamin a good choice for tiredness?

A multivitamin is a sensible starting point if your tiredness may be related to general dietary gaps rather than one specific deficiency. A good-quality multivitamin will cover the B vitamins, iron, vitamin D, and the other nutrients that support energy production in a single daily dose. For people who eat reasonably well but inconsistently, that broad coverage is useful.

The trade-off is that many multivitamins don't provide iron, B12, or vitamin D at the levels needed to correct an established deficiency. For that, targeted supplementation is the better route. For people with a busy lifestyle, inconsistent eating habits, or a diet that may be low in one or more nutrients without being overtly deficient, a multivitamin provides a solid baseline. It's the nutritional safety net most people benefit from but few people actually have.

OneVit Complete Multivitamin includes the full range of B vitamins, vitamin D3, and iron alongside 20+ additional micronutrients formulated for everyday support.

Who is most likely to benefit from vitamins for tiredness?

Not everyone who feels tired will benefit from a supplement, and that's worth being honest about. But certain groups are far more likely to have a nutritional shortfall that supplementation can address.

Women of reproductive age are at higher risk of iron deficiency due to menstrual blood loss. Tiredness, pallor, and difficulty concentrating are common early signs.

People following vegan or plant-based diets are at higher risk of B12 deficiency, since B12 is absent from plant foods without fortification, and they also have lower intake of haem iron, which is more readily absorbed than the non-haem iron found in plants.

People aged 60 and over absorb B12 less efficiently as stomach acid production declines with age. Vitamin D deficiency is also more common in this group due to reduced skin synthesis and lower dietary intake.

People who are rarely outdoors or who cover their skin are at heightened risk of vitamin D deficiency year-round, not just in the winter months. The type of UV light your skin needs to make vitamin D doesn't pass through glass, so sitting by a sunny window doesn't count.

Anyone on a restricted or inconsistent diet, including people who regularly skip meals, follow low-calorie diets, or rely heavily on convenience foods, may have insufficient intake across multiple B vitamins. The cumulative effect matters more here than any one nutrient.

How and when to take energy supplements

When and how you take your supplements affects how well they work. The basics aren't complicated.

B vitamins are water-soluble and best taken in the morning with food. Taking them earlier in the day avoids any potential mild stimulant effect from B12 interfering with sleep.

Iron is best taken on an empty stomach or with a vitamin C-rich drink such as orange juice, which significantly improves absorption. Avoid taking iron alongside tea, coffee, or calcium-rich foods, which reduce absorption. If iron causes digestive discomfort on an empty stomach, take it with a small amount of food. You'll absorb slightly less but you're more likely to keep taking it consistently.

Vitamin D is fat-soluble and absorbed best when taken with a meal that contains some fat. Breakfast with eggs or lunch with avocado both work well.

Multivitamins should be taken with food. This supports absorption of the fat-soluble vitamins (A, D, E, K) and reduces the chance of nausea from the iron content.

If you take prescription medication or have any ongoing health conditions, speak to your GP or a pharmacist before starting a new supplement. Some nutrients interact with medications.

Frequently Asked Questions

What are the best vitamins for energy and tiredness? The vitamins and minerals with the strongest evidence behind tiredness and fatigue reduction are iron, vitamin B12, other B vitamins (including niacin and B6), folate, and magnesium. The right choice depends on what's behind your tiredness. A blood test is the most reliable way to identify which nutrient you're running low on.

Do vitamins for tiredness actually work? They work when a nutritional deficiency is contributing to your tiredness. If your energy levels are low because of poor sleep, stress, or an underlying health condition, supplements won't fix that. But where there's a genuine shortfall in iron, B12, or vitamin D, addressing it through supplementation can produce a noticeable improvement over time.

How long do vitamins for tiredness take to work? It varies by nutrient and how depleted you were to start with. Iron supplementation starts to improve energy levels within 2 to 4 weeks, though full correction of a deficiency takes several months. B12 improvements can be felt within a few weeks. Vitamin D takes longer, with improvements building gradually over weeks to months.

Can I take iron and B12 together? Yes, there's no known interaction between iron and B12. They're both commonly included in multivitamin formulas together. If you're taking high-dose iron to address a confirmed deficiency, take it separately from calcium-rich foods or supplements for best absorption.

What vitamins help with tiredness in women? Iron is the most commonly relevant nutrient for women of reproductive age due to menstrual blood loss. B vitamins (particularly B12, B6, and folate), vitamin D, and magnesium are also widely relevant. If you're pregnant or planning a pregnancy, folate needs change significantly, so discuss this with your GP.

Is vitamin D good for tiredness? Vitamin D contributes to muscle function, and persistent deficiency is associated with fatigue and muscle weakness. It's not a direct energy booster like the B vitamins, but correcting a deficiency, common in the UK, can contribute to reduced physical tiredness over time.

Can I get enough B vitamins from my diet alone? Most people on a varied omnivorous diet get enough B vitamins from food. The main exceptions are B12, which is almost absent from plant foods, and folate, which can run low in diets light on green vegetables. If you follow a plant-based diet or have a digestive condition that affects absorption, B12 supplementation is sensible regardless of whether you currently feel tired.

When should I see a GP about tiredness? See your GP if your tiredness is persistent (lasting more than a few weeks), unexplained by lifestyle factors, or accompanied by other symptoms such as breathlessness, palpitations, unexplained weight loss, or pins and needles. These can point to underlying conditions supplements won't address.

References

  1. NHS. B vitamins and folic acid. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-b/
  2. UK Government. Great Britain Nutrition and Health Claims (NHC) Register. https://www.gov.uk/guidance/great-britain-nutrition-and-health-claims-nhc-register
  3. Kennedy DO. B vitamins and the brain: mechanisms, dose and efficacy. A review. Nutrients. 2016;8(2):68. doi:10.3390/nu8020068
  4. Tardy A-L, Pouteau E, Marquez D, Yilmaz C, Scholey A. Vitamins and minerals for energy, fatigue and cognition: a narrative review of the biochemical and clinical evidence. Nutrients. 2020;12(1):228. doi:10.3390/nu12010228
  5. NHS. Iron deficiency anaemia. https://www.nhs.uk/conditions/iron-deficiency-anaemia/
  6. Scientific Advisory Committee on Nutrition. Iron and Health. London: TSO; 2010. https://www.gov.uk/government/publications/sacn-iron-and-health-report
  7. Demirdjian SP, Kerr MA, Mulhern MS, Thompson PD, Ledwidge M, McCann MT. Association between adiposity and iron status in women of reproductive age: data from the UK National Diet and Nutrition Survey (NDNS) 2008–2019. J Nutr. 2024;154(11):3409–3418. doi:10.1016/j.tjnut.2024.08.026
  8. Hallberg L, Brune M, Rossander L. Effect of ascorbic acid on iron absorption from different types of meals. Studies with ascorbic-acid-rich foods and synthetic ascorbic acid given in different amounts with different meals. Hum Nutr Appl Nutr. 1986;40(2):97–113. https://pubmed.ncbi.nlm.nih.gov/3700141/
  9. Pineda O, Ashmead HD. Effectiveness of treatment of iron-deficiency anemia in infants and young children with ferrous bis-glycinate chelate. Nutrition. 2001;17(5):381–384. doi:10.1016/S0899-9007(01)00519-6
  10. Wu S, Sun B, Yang Q, et al. The effect of vitamin D supplementation on fatigue: a systematic review and meta-analysis. Front Nutr. 2023;10:1222409. doi:10.3389/fnut.2023.1222409
  11. UK National Diet and Nutrition Survey. Public Health England / Food Standards Agency. https://www.gov.uk/government/collections/national-diet-and-nutrition-survey
  12. NHS. Vitamin D. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
  13. NHS. Vitamin B12 or folate deficiency anaemia. https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/
  14. Baik HW, Russell RM. Vitamin B12 deficiency in the elderly. Annu Rev Nutr. 1999;19:357–377. doi:10.1146/annurev.nutr.19.1.357
  15. Allen LH. How common is vitamin B-12 deficiency? Am J Clin Nutr. 2009;89(2):693S–696S. doi:10.3945/ajcn.2008.26947A
  16. The Vegan Society. Vitamin B12. https://www.vegansociety.com/resources/nutrition-and-health/nutrients/vitamin-b12

This article is for informational purposes only and does not constitute medical advice. If you are concerned about persistent tiredness or fatigue, consult a GP or qualified healthcare professional.

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