Vitamin D3 vs D2: Which Form Is Better?
Introduction
Vitamin D3 (cholecalciferol) Vitamin D is not a single substance but a family of compounds with similar structures. The two forms relevant to human health are VitaminD2 and vitamin D3 (ergocalciferol). Both are converted in the liver and kidney into the active hormone calcitriol, which helps regulate calcium levels, support muscle and nerve function and maintain strong bones. However, there are important differences in their sources, bioavailability and suitability for different diets.
Vitamin D deficiency. This article compares vitamin D3 and vitamin D2 in the context of UK nutritional guidance. It draws on evidence from the British Nutrition Foundation (BNF), National Institute for Health and Care Excellence (NICE) guidelines and the latest Bedfordshire, Luton and Milton Keynes (BLMK) Area Prescribing Committee guideline (May 2025). Use the internal links throughout this guide to explore related topics such as symptoms, recommended daily vitamin D intake and sources of vitamin D.
What Are Vitamin D3 and Vitamin D2?
Chemical Differences and Sources
Vitamin D3 and vitamin D2 share a common sterol backbone, but differ in the arrangement of their side chains. These structural differences affect where each form is found and how efficiently it is converted to the active hormone.
- Vitamin D3 (cholecalciferol) is produced naturally in human skin when ultraviolet‑B (UVB) light (290–315 nm) from sunlight strikes 7‑dehydrocholesterol, converting it to pre‑vitamin D3[1]. It is only found naturally in animal‑derived foods such as oily fish, meat and egg yolk[2]. Most vitamin‑D supplements available in the UK contain vitamin D3 derived from lanolin (sheep wool fat), making them unsuitable for strict vegans[3].
- Vitamin D2 (ergocalciferol) is produced by irradiating ergosterol in yeast or fungi. It occurs naturally in sun‑exposed mushrooms and is used to fortify some plant‑based dairy alternatives[4]. Because it is derived from fungi, vitamin D2 is suitable for vegetarians and vegans, and lichen‑derived vitamin D3 supplements provide a vegan alternative [5].
How the Body Processes Each Form
Although vitamin D3 and vitamin D2 have different origins, both forms are biologically inert until they are hydroxylated in the body. The liver converts them to 25‑hydroxyvitamin D (25(OH)D), the main circulating form used to assess vitamin D status, and the kidneys convert this to the active hormone 1,25‑dihydroxyvitamin D (calcitriol)[6]. Once converted to calcitriol, both forms help absorb calcium from the intestine, regulate parathyroid hormone and support bone and immune health.
Which Form Is More Effective?
The British Nutrition Foundation reviewed evidence from supplementation trials and concluded that vitamin D3 is generally more effective than vitamin D2 at raising concentrations of 25‑hydroxyvitamin D in the blood[7]. A 2012 meta‑analysis cited by the BNF found that vitamin D3 supplementation increased serum 25(OH)D levels more efficiently than vitamin D2[7].
Why might vitamin D3 work better?
- Higher affinity for binding proteins: vitamin D3 appears to have a greater affinity for vitamin D binding proteins in the bloodstream, leading to more stable circulating levels.
- Longer half‑life: vitamin D3’s metabolites tend to remain in the circulation longer than those of vitamin D2, enabling a more sustained rise in 25(OH)D.
- Efficient conversion: research suggests that vitamin D3 is more efficiently converted to active metabolites.
That said, vitamin D2 still raises serum vitamin D levels and can treat conditions like rickets and osteomalacia. For most adults who follow a mixed diet, vitamin D3 supplements are preferred; vegans may choose vitamin D2 or lichen‑derived vitamin D3[5].
Dietary Sources of Vitamin D2 and Vitamin D3
Vitamin D3 (Animal‑Based and Sunlight)
In the UK, natural food sources of vitamin D3 are limited. They include:
- Oily fish (salmon, trout, mackerel, sardines), liver, red meat and egg yolks[2].
- Fortified foods, such as some breakfast cereals, milk and alternative drinks, fat spreads and infant formula[8].
- Sunlight exposure: Synthesis of vitamin D3 in the skin is the primary source for most people. However, at UK latitudes this only occurs between April and September around midday when UVB levels are high[9]. During autumn and winter sunlight is too weak, and vitamin D must come from diet or supplements.
Vitamin D2 (Plant‑Based)
Sources of vitamin D2 include:
- UV‑exposed mushrooms (e.g., portobello mushrooms labelled “rich in vitamin D”).
- Fortified plant‑based drinks and spreads, such as soya milk, oat milk and vegetable spreads[4].
- Yeast or fungal supplements used in over‑the‑counter vitamin D2 preparations.
While vitamin D2 is suitable for vegetarians and vegans, its concentration in food is generally lower than vitamin D3 in animal foods. Therefore, fortified products or supplements are often required to meet the recommended intake.
Vitamin D Supplements in the UK: Dosage and Guidelines
Government Recommendations
Public health advice in the UK remains 10 micrograms (400 IU) of vitamin D per day for adults and children aged four and over[10]. Infants under one year require 8.5-10 µg/day[11]. This reference nutrient intake (RNI) is designed to ensure that 97.5 % of the population have sufficient vitamin D for musculoskeletal health.
In May 2025 the Bedfordshire, Luton and Milton Keynes (BLMK) Area Prescribing Committee issued updated guidance confirming that all adults living in the UK should take a 400‑unit (10 µg) vitamin D supplement during autumn and winter, and those at higher risk of deficiency should take it all year round[12]. Maintenance supplementation for people recovering from deficiency typically ranges from 800 -2000 IU (20 -50 µg) of vitamin D3 daily[13].
Choosing a Supplement: D3 vs D2
Vitamin D3 is generally preferred because it is more effective at raising and maintaining serum vitamin D levels[7]. However, for people following a vegan diet, vitamin D2 or lichen‑derived vitamin D3 supplements are appropriate[5]. The BLMK guideline notes that traditional vitamin D3 supplements are derived from lanolin and are not suitable for vegans, and there are currently no licensed D3 products suitable for vegans; unlicensed food supplements are available[14].
When selecting a supplement:
- Check the source: the label should specify whether the product contains vitamin D3 (colecalciferol) or vitamin D2 (ergocalciferol). Vegan D3 products should state they are derived from lichen or algae.
- Ensure an appropriate dose: standard OTC products contain 10 µg (400 IU) per tablet, though those recovering from deficiency may require higher doses under medical supervision[13].
- Avoid unnecessary additives: some formulations include calcium; if you already consume sufficient calcium through diet, separate vitamin D may be preferable. People with allergies should check for peanut or soya ingredients [14].
Plant‑Based Diets and Vegan Considerations
People following plant‑based diets often struggle to obtain enough vitamin D from food alone. The British Dietetic Association’s guidance on plant‑based diets notes that everyone should consider taking a 10 µg vitamin D supplement during autumn and winter, and highlights that vitamin D2 and lichen‑derived vitamin D3 are suitable for vegans[5]. Sun‑exposed mushrooms and fortified plant drinks can contribute, but they may not provide the full daily requirement.
The British Nutrition Foundation explains that vitamin D3 is only found naturally in animal‑derived foods and most supplements are derived from sheep wool[3]. Because of this, vegans and some vegetarians should look for supplements clearly labelled as vegan, either containing vitamin D2 or D3 from lichen. The BLMK guideline adds that there are no licensed D3 products suitable for vegans, but unlicensed food‑supplement options are available[14].
Safety, Side Effects and Toxicity
Vitamin D toxicity is rare but can occur if large doses are taken for prolonged periods. Symptoms of excessive vitamin D intake include nausea, vomiting, muscle weakness, confusion and excessive thirst, and result from high blood calcium levels. To avoid toxicity:
- Stick to recommended doses: The UK’s safe upper limit for adults is generally 4,000 IU (100 µg) per day unless under medical supervision.
- Avoid high‑dose injections without specialist advice: The BLMK guideline cautions that intramuscular vitamin D2 injections are not recommended because absorption is unpredictable and can lead to toxicity[15].
- Check medication interactions: Certain medicines -such as antiepileptic drugs and corticosteroids – can reduce vitamin D levels or increase the risk of hypercalcaemia[16].
If you are pregnant, breastfeeding or have chronic conditions such as kidney or liver disease, consult a healthcare professional before taking high‑dose supplements.[17].
Frequently Asked Questions (FAQs)
Is vitamin D3 better than vitamin D2?
Evidence suggests vitamin D3 raises serum 25(OH)D more effectively than vitamin D2[7]. Therefore, vitamin D3 is usually the preferred supplement. However, vitamin D2 still increases vitamin D levels and is suitable for vegans and vegetarians. For people on plant‑based diets, lichen‑derived vitamin D3 offers a vegan alternative.
Are vitamin D supplements necessary in the UK?
Yes. Because the UK’s northerly latitude limits sunlight synthesis during autumn and winter, the NHS recommends that all adults and children aged four and over take 10 µg of vitamin D daily[10]. Those at risk of deficiency (older adults, people with darker skin, those who stay indoors or cover their skin, pregnant or breastfeeding women) should take supplements all year round[12].
Do mushrooms provide vitamin D3 or vitamin D2?
Mushrooms produce vitamin D2 when exposed to UV light. They do not contain vitamin D3. Choose mushrooms marketed as “rich in vitamin D” or “UV‑treated” to ensure a meaningful contribution to your intake[4].
Can I meet my vitamin D needs through diet alone?
It is challenging. Even with oily fish, eggs and fortified foods, the National Diet and Nutrition Survey shows that average intakes in all UK age groups are below the RNI[18]. Therefore, supplements are recommended to achieve adequate levels, especially in winter.
Are there vegan vitamin D3 supplements?
Yes, some unlicensed vitamin D3 products are derived from lichen, making them suitable for vegans[5]. Always check the product label to verify the source. Standard lanolin‑derived vitamin D3 supplements are not vegan-friendly[14].
Conclusion and Internal Links
In summary, both vitamin D3 and vitamin D2 help maintain healthy bones, muscles and immune function, but vitamin D3 tends to raise blood vitamin D levels more efficiently. Most people can safely take a 10 µg supplement during autumn and winter and should choose vitamin D3 unless they follow a vegan diet. Remember that vitamin D is just one part of a healthy lifestyle; eating a balanced diet rich in calcium and getting safe sun exposure are also essential.
For more in‑depth information on vitamin D, explore our related articles:
- Vitamin D Guide: Benefits, Deficiency & Supplements -a comprehensive overview covering all aspects of vitamin D.
- Symptoms and Risks of Vitamin D Deficiency -recognise signs of deficiency and when to get tested.
- How Much Vitamin D Do You Need Daily? -understand recommended daily intake for different groups.
- Top Sources of Vitamin D: Food, Sun & Supplements -learn how to obtain vitamin D from diet and lifestyle.
- Who’s at Risk of Vitamin D Deficiency in the UK? -identify groups who need supplements year‑round.
- Vitamin D Supplement FAQs -answers to common questions about using supplements safely.
Always speak to a healthcare professional or pharmacist before starting high‑dose vitamin D therapy, and consult our Vitamin D supplement FAQ for safe use guidelines.
References
[1] [2] [3] [6] [7] [8] [9] [10] [11] vitamin-d-and-immunity_qa.pdf
https://www.nutrition.org.uk/media/1tuj1zrs/vitamin-d-and-immunity_qa.pdf
https://www.uhsussex.nhs.uk/wp-content/uploads/2023/03/plant-based-diets-bda.pdf
[12] [13] [14] [15] [16] [17] Vitamin-D-Deficiency-in-Adults-in-Primary-Care-May-2025.pdf
[18] NDNS: results from years 9 to 11 (combined) – statistical summary – GOV.UK