Vitamin D3 vs D2: Which Form Should You Take in the UK?

For most adults, D3 (cholecalciferol) is the better default. Evidence reviewed by UK health bodies suggests it raises blood vitamin D levels more than D2 (ergocalciferol). D2 still works. It is made without animal products, so it suits some vegans and vegetarians. A vegan D3 made from lichen also exists. This guide covers the differences, the evidence, the UK dose guidance and what to check on a label.

Key Takeaways

  • D3 and D2 both raise vitamin D levels. Most evidence shows D3 raises them more and keeps them higher for longer.
  • D3 usually comes from lanolin (sheep’s wool) or lichen. D2 comes from fungi or yeast. Lichen-derived D3 is the plant-based D3 option.
  • UK guidance suggests 10 micrograms (400 IU) a day in autumn and winter. Some people need it all year.
  • The MHRA advises adults not to exceed 100 micrograms (4,000 IU) a day unless prescribed more.
  • Check the form, the dose per serving and the source on the label. Ask a pharmacist if you take prescribed medicines.

Table of Contents

What is the difference between vitamin D2 and D3?

Vitamin D is a family of compounds. Two forms matter for supplements.

  • D2 (ergocalciferol) is made by plants, fungi and yeast.
  • D3 (cholecalciferol) is the form your skin makes when it is exposed to sunlight. It is also found in animal foods.

The two differ slightly in structure. D2 has a double bond between carbon atoms 22 and 23 in its side chain and an extra methyl group. The GOV.UK SACN rapid review describes this and notes that both forms increase total serum 25(OH)D, the blood marker used to judge vitamin D status. How they compare in efficacy is still debated.

The small chemical difference changes how the body handles each form. That is why researchers have compared them for years.

Quick comparison

Vitamin D2 Vitamin D3
Chemical name Ergocalciferol Cholecalciferol (colecalciferol)
Typical source in supplements Fungi, UVB-irradiated yeast Lanolin (sheep’s wool) or lichen
Made in human skin No Yes, with sunlight
Natural food sources Low amounts Oily fish, fish liver oil, egg yolk
Effect on blood levels Raises 25(OH)D Raises 25(OH)D, usually by more
Vegan suitability Generally yes Only if lichen-derived

The sources in the table follow the SACN review, which says D3 in supplements and fortified foods is mainly derived from lanolin. D2 comes from fungi and UVB-irradiated yeast. Vegan D3 can be obtained from lichen.

Which one raises vitamin D levels more?

The weight of evidence favours D3.

A 2021 systematic review and meta-analysis of 24 studies with 1,277 participants found D3 more effective than D2 at improving total 25(OH)D. The mean difference was 15.69 nmol/L. It also reduced parathyroid hormone levels. The result held across different participant groups, doses and delivery formats.

An earlier 2012 meta-analysis in the American Journal of Clinical Nutrition reached a similar conclusion. It found a significant advantage for D3 with a weighted mean difference of 15.23 nmol/L. The effect was clear for single large doses and was lost with daily supplementation. The authors said D3 could become the preferred choice and called for more research on age, sex and ethnicity.

The NIH Office of Dietary Supplements states that both forms are well absorbed in the small intestine and that fat in the gut helps absorption. It adds that most evidence indicates D3 raises serum 25(OH)D to a greater extent and maintains higher levels longer than D2.

How much weight to put on the numbers

The SACN review reports the same pooled difference of 15.69 nmol/L. It also notes very high heterogeneity between studies (I² of 94%). That means the average may not hold across every dose and schedule. The practical reading:

  • D3 is probably the more efficient form.
  • D2 is still effective at raising levels and preventing deficiency.
  • The size of the gap depends on dose and schedule.

SACN’s overall view is that D3 may be more efficacious. It also says both forms are effective in raising 25(OH)D and so in preventing deficiency, defined as below 25 nmol/L.

What does absorption have to do with it?

Absorption in the gut is not the main reason for the gap. Both forms are absorbed well. The difference shows up in how much 25(OH)D ends up in the blood and how long it stays there.

Two habits improve absorption of either form:

  1. Take it with a meal that contains some fat. The NIH fact sheet linked above notes that fat in the gut enhances absorption.
  2. Take it at the same time each day, so it becomes routine.

For the wider question of why the form and chemistry of a supplement matter more than the capsule it comes in, see our guide to bioavailable supplements.

What do UK clinical guidelines prefer?

UK prescribing guidance leans towards D3.

These documents are about treating diagnosed deficiency. If a GP or pharmacist has told you that you are deficient, follow their advice on product and dose.

D2 or D3 if you are vegan or vegetarian?

This is where D2 earns its place.

The NHS Specialist Pharmacy Service explains that D3 is produced from 7-dehydrocholesterol taken from lanolin (wool fat) or from lichen. Wool-fat products may be unacceptable to vegans. They may be acceptable to vegetarians if the sheep are not slaughtered. D2 comes from fungi or yeast and is likely to be acceptable to both groups. The British Nutrition Foundation’s guidance on vegan diets makes the same point: the usual D3 comes from sheep’s wool.

There are three practical routes for a plant-based diet:

  1. Lichen-derived D3. It gives the D3 form without animal sources. Look for the word “lichen” or a vegan certification on the label.
  2. D2 from yeast or fungi. It is plant-based and effective, though evidence suggests it raises levels less than D3.
  3. Fortified foods. Check the label, as the form used varies.

A label that says only “vitamin D3” does not tell you the source. If it matters to you, check for a statement about lichen or lanolin, or look for a vegan logo.

How much vitamin D should you take in the UK?

The form matters less than taking a sensible amount at the right time of year.

The GOV.UK migrant health guide advises everyone to consider a daily 10 microgram (400 IU) supplement from October to early March. People with little or no sun exposure should consider one all year round.

The NHS North West London guideline goes further. Adults at higher risk should take 10 micrograms daily throughout the year. Other adults should consider it, particularly in autumn and winter.

On the upper limit, the MHRA advises adults not to take more than 100 micrograms (4,000 IU) per day unless prescribed a higher dose. It also advises checking product labels carefully. The UK industry body CRN UK describes how the 100 microgram upper level for food supplements rests on randomised trial data showing a wide safety margin.

How much vitamin D should you take in the UK?

Micrograms or IU?

Labels often show both. The conversion is simple: 10 micrograms equals 400 IU, and 100 micrograms equals 4,000 IU. A tablet labelled “1,000 IU” holds 25 micrograms. Add up every product you take, including multivitamins and fortified foods, so the total stays within the guidance.

Vitamin D microgram and IU conversions

How to choose a vitamin D supplement

Use this checklist when you compare products.

  1. Form. D3 for most adults. D2 or lichen-derived D3 if you follow a vegan diet.
  2. Dose per serving. Read it in micrograms. Check how many tablets, capsules or drops make up one serving.
  3. Source. Look for a statement on lanolin or lichen if it matters to you.
  4. Format. Oil-based capsules and drops pair well with a meal containing fat. Tablets are simple and stable.
  5. Quality marks. Independent certification and batch testing show that a product is made to a documented standard. Our guide on how to choose supplements walks through what to look for on a UK label.
  6. Other ingredients. Check allergens, fillers and added nutrients.

Real-world examples

  • An office worker in Manchester who rarely gets midday sun in winter could take 10 micrograms daily from October to early March, as the GOV.UK guidance suggests. A D3 product with a clear dose fits this.
  • A vegan in Bristol can choose a lichen-derived D3 or a D2 product, and confirm the source on the label or with the maker.
  • Someone who covers most of their skin outdoors, or rarely goes out, falls into the group GOV.UK says should consider a supplement all year.

What about D3 with K2?

Many products combine D3 with vitamin K2. Readers ask whether the pairing is worthwhile. We found no UK regulator or health body source in our research that sets out proven benefits of the combination. So the decision is best based on the basics: the D3 dose, the form and the quality of the product.

If you choose a combined product, check the dose of each nutrient separately. Keep the vitamin D total under the 100 microgram daily ceiling from the MHRA. If you take prescribed medicines, speak to a pharmacist before starting any new supplement. This applies especially to blood thinners, heart medicines, thyroid medicines and cholesterol medicines. Readers often ask about specific drugs such as diltiazem, methimazole or rosuvastatin (Crestor). A pharmacist can check your exact prescription, and that is the quickest route to a reliable answer.

Our perspective

We approach vitamin D the way we approach every supplement: start with the form, the dose and what the body can actually use.

The D3 versus D2 question shows why. Both forms are real vitamin D, and both raise blood levels. The evidence points to D3 doing it more efficiently, so we treat D3 as the sensible starting point for most adults. We also think people on a vegan diet deserve a clear answer about the source, not a vague label.

Our approach is preventative. We believe in building good habits early, in autumn, before levels drop, rather than reacting later. That means reading labels, knowing your daily dose in micrograms and choosing products from makers that publish their standards. We hold ourselves to certifications such as GMP and FSSC 22000, and to batch-by-batch testing, because a label only helps when the product matches it.

Vitamin D is one part of a routine. Sleep, movement, food and the right supporting nutrients all count. Start with the basics, keep the doses sensible and review your routine with a pharmacist or GP if your circumstances change.

Tinashe

Build a routine that fits you

Our range is organised by need: energy, sleep, immune support, bones and joints, healthy ageing, stress, digestion and more. All of it is formulated with bioavailability in mind, and every product is tested and made to certified standards. Our supplements are vegan and GMO-free where stated on the product page.

Vitamin B Complex — B1 to B12 + Inositol, 90 Vegan Tablets

Browse the full thecary range by category to find products for your goals. If you are building a daily routine, the Vitamin B Complex is a vegan option covering B1 to B12 plus inositol. To see how a multi-nutrient approach compares with single nutrients, read our guide to greens powder versus multivitamin and how the label shows the dose.

FAQ

Which vitamin D is better, D2 or D3?

For most people D3 is the better choice. Meta-analyses show it raises blood levels more than D2, and UK clinical guidance prefers it for treating deficiency. D2 remains effective and is a reasonable option on a vegan diet.

Is there a plant-based vitamin D3?

Yes. D3 can be made from lichen instead of lanolin from sheep’s wool. The label should state the source or carry a vegan mark. If it only says “vitamin D3”, the source is unclear, so check with the maker.

Does the form affect absorption?

Both D2 and D3 are absorbed well in the small intestine, and taking either with food that contains fat helps. The difference lies in how much 25(OH)D reaches the blood and how long it stays there. D3 generally does better on both counts.

How much vitamin D can I take safely?

UK guidance suggests 10 micrograms (400 IU) a day, mainly from October to early March, or all year for some people. The MHRA advises adults not to exceed 100 micrograms (4,000 IU) a day unless prescribed more. Count every product you take.

Can I take vitamin D with prescribed medicines?

This depends on the medicine and your health. Ask a pharmacist or GP before you start, and bring the product label with you. They can check your prescription for interactions.

Sources

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