Iron, B12, or Vitamin D? Which Supplement You Actually Need for Energy

If you're tired all the time and your sleep is broadly fine, a nutrient deficiency is one of the more likely explanations. Iron, B12, and vitamin D are the three that come up most in the UK — and they get lumped together in supplement marketing when they're actually quite different problems affecting different systems.

Taking the wrong one won't hurt you, but it won't help either. Here's how to tell them apart, work out which one applies to you, and know what to take if you can't get a GP appointment for weeks.

The right answer is a blood test. If you can get one via your GP — and you should ask — it'll tell you exactly what's low and save you guessing. But if you're in that situation where you're tired, the NHS wait is weeks, and you want to do something in the meantime, the following is a reasonable framework.

Vitamin D: the UK's most common deficiency

According to UK government nutritional surveys, roughly one in five adults has low vitamin D levels. That figure rises sharply through autumn and winter, when there's not enough UV light in the UK for your skin to synthesise the vitamin at all — the sun simply isn't strong enough between October and March above roughly 51°N (that's roughly London).

The UK government recommends 10mcg (400 IU) daily for all adults year-round.

Who's most at risk

• Anyone who spends most daylight hours indoors
• People with darker skin (melanin reduces vitamin D synthesis)
• Anyone in the UK from October to April — basically all of us
• The elderly, and those who cover most of their skin

Symptoms of vitamin D deficiency

Persistent fatigue, low mood (especially in winter), muscle weakness, frequent illness, bone aches. The fatigue is often described as a general heaviness rather than the acute brain fog of iron deficiency.

What to take

Vitamin D3 (cholecalciferol) is the form your body makes from sunlight and is more effective at raising serum levels than D2. Take it with a meal containing fat — it's fat-soluble, so absorption is poor on an empty stomach.

For most people, 1,000-2,000 IU daily is a sensible maintenance dose through winter. If you've had a blood test showing genuine deficiency (below 25 nmol/L), your GP may prescribe a higher loading dose initially.

The BetterYou DLux oral spray is a popular UK option — sublingual delivery absorbs well and bypasses any gut absorption issues. Vitabiotics Ultra D3 tablets at 1,000 IU are cheap and reliable for daily maintenance. For those confirmed deficient and wanting to correct it faster, 4,000 IU formulations are available without prescription in the UK, though staying on high doses long-term without monitoring isn't recommended.

Iron: the most common deficiency worldwide

Iron deficiency is the most widespread nutritional deficiency globally, and in the UK it disproportionately affects women of childbearing age — estimates suggest around a quarter have depleted iron stores, though full iron-deficiency anaemia affects fewer.

Who's most at risk

• Women with heavy periods
• Vegans and vegetarians (plant-based iron is less bioavailable than haem iron from meat)
• Pregnant women and those who have recently given birth
• Endurance athletes
• Anyone with a condition affecting gut absorption (coeliac disease, inflammatory bowel disease)

Symptoms of iron deficiency

Fatigue and low energy are the headline symptoms, but brain fog, difficulty concentrating, pallor (check inside your lower eyelid — if it's pale rather than pink, that's a flag), shortness of breath on light exertion, and cold hands and feet are all associated. Hair loss and brittle nails in chronic deficiency.

What to take

Iron supplements come in several forms. Ferrous sulphate is the standard NHS prescription form — cheap and effective, but causes constipation and stomach cramps in a significant proportion of people. Ferrous gluconate and iron bisglycinate are gentler options available over the counter. Bisglycinate in particular has good absorption and much fewer side effects.

Spatone is a liquid iron supplement from a natural iron-rich spring water source in Wales. The dose per sachet is low (5mg elemental iron, versus 65mg in ferrous sulphate), but it's very gentle and well-tolerated — useful for mild deficiency or for people who can't tolerate standard supplements. It comes in an apple flavour variant that most people find easier than plain.

Take iron with vitamin C to improve absorption (orange juice, or a vitamin C supplement). Avoid taking it with calcium-rich foods or supplements — dairy, antacids — as calcium directly blocks iron absorption.

Important: Don't take high-dose iron supplements without a blood test confirming deficiency or low stores. Iron accumulates in the body and excess iron is genuinely harmful. The precaution is real.

Vitamin B12: the quiet deficiency

B12 deficiency is less common than vitamin D and iron, but it mimics both in its primary symptom: fatigue. According to the NHS, around 1 in 20 people aged 65-74 and 1 in 10 aged 75 or over are B12 deficient. Among vegans and vegetarians the rate is substantially higher at any age — B12 is found almost exclusively in animal products.

Who's most at risk

• Vegans and vegetarians
• The elderly (stomach acid declines with age, reducing B12 absorption)
• People taking metformin for type 2 diabetes (it reduces B12 absorption)
• Anyone with pernicious anaemia (an autoimmune condition that destroys the intrinsic factor needed for B12 absorption)
• Those with Crohn's disease or other conditions affecting the terminal ileum

Symptoms of B12 deficiency

Fatigue, weakness, and brain fog — similar to iron. But B12 deficiency also causes neurological symptoms that iron deficiency doesn't: tingling or numbness in hands and feet, difficulty with balance, and mood changes including depression. If neurological symptoms are present alongside fatigue, get a blood test promptly — prolonged B12 deficiency can cause nerve damage.

What to take

Two main forms: cyanocobalamin (synthetic, stable, cheap, converts to active B12 in the body) and methylcobalamin (already in active form, no conversion needed, slightly better absorbed). For most people both work fine. If you have an MTHFR gene variant affecting methylation, methylcobalamin is preferable — but most people don't know whether they have this.

High-street doses are typically 500-1,000mcg. B12 is water-soluble and the body excretes what it doesn't use, so the upper dose range is safe. Sublingual (dissolving under the tongue) tablets are absorbed well. If deficiency is confirmed as pernicious anaemia, the NHS provides B12 injections which bypass absorption issues entirely.

How to choose without a blood test

If you want to make an educated guess while waiting for a GP appointment:

Take vitamin D if: You're in the UK, it's October to April, you work indoors, and your fatigue is generalised and seasonal. Almost everyone in the UK is low on vitamin D in winter. The risk of taking 1,000-2,000 IU daily is negligible; the upside is meaningful.

Consider iron if: You're a woman with heavy periods, you've recently been pregnant, you're vegetarian or vegan, or your fatigue is accompanied by pallor, breathlessness, or brain fog. Don't self-dose high iron without a test — but a gentle form like bisglycinate at a maintenance dose is low risk.

Consider B12 if: You're vegan or vegetarian (treat it as a given that you need to supplement), you're over 60, or fatigue is accompanied by neurological symptoms like tingling or numbness.

Consider a multivitamin if: You're not sure and you want a baseline. Wellwoman and Wellman from Vitabiotics cover vitamin D, iron, and B12 at moderate doses — not sufficient to correct established deficiency, but useful for general nutritional insurance. Wellman Energy adds B6 and magnesium which play a role in energy metabolism.

Combining supplements

Vitamin D is generally safe to combine with iron and B12 — no negative interactions. Take vitamin D with food, iron between meals or with vitamin C, and B12 whenever suits you.

For more on which vitamins are worth taking specifically for tiredness — including wider options beyond these three — see our guide to vitamins for tiredness UK.

If fatigue persists despite correcting deficiencies and you're sleeping enough, see a GP. Persistent unexplained fatigue can indicate thyroid conditions, coeliac disease, diabetes, or other treatable conditions that a blood panel will flag. It's also worth having a read of why you're always tired — the causes of chronic fatigue extend well beyond supplements.

Frequently asked questions

Can I take iron, B12, and vitamin D together? Yes, there are no significant negative interactions between the three. The main practical note is to take iron away from calcium-rich foods, and to take vitamin D with a meal containing fat for best absorption.

How long before supplements improve my energy levels? Vitamin D: 4-8 weeks for noticeable improvement in deficient individuals. Iron: 2-4 weeks for energy symptoms to improve, though blood levels can take 3-6 months to fully normalise. B12: a few weeks for energy, longer for any neurological symptoms.

Is Spatone as effective as iron tablets? Spatone provides much lower elemental iron per dose than standard tablets (around 5mg vs 65mg). For mild deficiency or iron maintenance, it's effective and much gentler on the gut. For treating moderate to severe iron deficiency anaemia, standard ferrous sulphate or bisglycinate at higher doses is more appropriate.

Do I need a prescription for iron supplements in the UK? No — iron supplements are available over the counter. The NHS may prescribe ferrous sulphate if deficiency is confirmed. High-dose iron should ideally follow a blood test, but standard over-the-counter iron supplements are freely available.

What's the difference between vitamin D2 and D3? D3 (cholecalciferol) is the form your skin synthesises from sunlight and is more effective at raising and maintaining blood levels than D2 (ergocalciferol, derived from plant sources). Most UK supplements use D3. For vegans, vegan D3 derived from lichen is available.