Ergocalciferol, also known as vitamin D2, is a plant-derived form of vitamin D prescribed in the UK to prevent and treat vitamin D deficiency. Unlike vitamin D3 (cholecalciferol), ergocalciferol is synthesised from plant sterols and fungi, making it suitable for vegetarians and vegans. It works by enhancing calcium absorption and supporting bone health, helping to prevent conditions such as osteomalacia in adults and rickets in children. Whilst cholecalciferol is generally preferred in UK clinical practice, ergocalciferol remains an important alternative, particularly for those requiring plant-based options. This article explains how ergocalciferol works, when it is prescribed, and how to take it safely.

What Is Ergocalciferol and How Does It Work?

Ergocalciferol, also known as vitamin D2, is a form of vitamin D used to prevent and treat vitamin D deficiency in the UK. Unlike cholecalciferol (vitamin D3), which is derived from animal sources or produced in the skin upon sun exposure, ergocalciferol is synthesised from plant sterols and fungi, making it suitable for vegetarians and vegans.

Vitamin D plays a crucial role in maintaining bone health by regulating calcium and phosphate metabolism. Without adequate vitamin D, the body cannot absorb sufficient calcium from the diet, potentially leading to conditions such as rickets in children and osteomalacia in adults. Ergocalciferol works by being converted in the liver to 25-hydroxyvitamin D (calcidiol), and subsequently in the kidneys to the active hormone 1,25-dihydroxyvitamin D (calcitriol). This active form enhances intestinal calcium absorption, promotes bone mineralisation, and contributes to normal immune function.

In the UK, cholecalciferol (vitamin D3) is generally preferred for treating vitamin D deficiency due to its greater efficacy in raising serum vitamin D levels. However, ergocalciferol is available on prescription and is listed in the British National Formulary (BNF) as an alternative, particularly for those requiring a plant-based option. The MHRA regulates its use, ensuring that formulations meet safety and efficacy standards. Treatment is typically initiated when blood tests reveal low serum 25-hydroxyvitamin D levels, defined by UK guidance as below 25 nmol/L for deficiency or 25–50 nmol/L for insufficiency.

Key points about ergocalciferol:

• It is a plant-derived form of vitamin D suitable for those following plant-based diets

• Requires conversion in the liver and kidneys to become biologically active

• Addresses deficiency by improving calcium absorption and bone health

• Regulated by the MHRA and prescribed according to NICE guidance

How to Take Ergocalciferol Safely

Dosing regimens for ergocalciferol vary depending on the severity of deficiency and individual patient factors. In the UK, NICE guidance recommends that treatment should be tailored to serum vitamin D levels and clinical presentation. For adults with vitamin D deficiency, a typical loading regimen involves a total of 300,000 IU, often given as ergocalciferol 50,000 IU (1.25 mg) once weekly for 6 weeks, followed by maintenance therapy. Maintenance doses are usually lower, ranging from 800–2,000 IU daily, though this may be adjusted based on clinical response.

Ergocalciferol is available in various formulations including capsules, tablets, and oral solutions. It should be taken with food, particularly meals containing some fat, as vitamin D is fat-soluble and absorption is enhanced in the presence of dietary lipids. Patients should swallow capsules whole with water and avoid crushing or chewing them unless specifically instructed otherwise.

Important safety considerations when taking ergocalciferol:

• Timing: Take at the same time each day (for daily dosing) or on the same day each week (for weekly dosing) to maintain consistency

• Missed doses: If you miss a dose, take it as soon as you remember unless it is almost time for the next dose—never double up

• Monitoring: Your GP should check your adjusted serum calcium before treatment and about 1 month after completing loading doses or starting therapy

• Drug interactions: Inform your doctor about all medications, particularly:

• Thiazide diuretics (may increase risk of hypercalcaemia)
• Digoxin (increased risk of toxicity if hypercalcaemia develops)
• Anticonvulsants, rifampicin or other enzyme inducers (may reduce vitamin D effectiveness)
• Orlistat or bile acid sequestrants like cholestyramine (may reduce absorption; take vitamin D several hours apart)

Some ergocalciferol preparations may contain peanut or soya oil. If you have allergies to these ingredients, check the patient information leaflet or ask your pharmacist about the specific product prescribed.

Patients should store ergocalciferol in a cool, dry place away from direct sunlight and keep it out of reach of children. Always follow the specific instructions provided by your prescriber or pharmacist, as individual requirements may differ from standard regimens.

Side Effects and Safety Considerations

Ergocalciferol is generally well-tolerated when taken at recommended doses, with most patients experiencing no adverse effects. However, as with any medication, side effects can occur, particularly if excessive doses are taken over prolonged periods, leading to vitamin D toxicity (hypervitaminosis D).

Common side effects are rare at therapeutic doses but may include:

• Mild gastrointestinal disturbances such as nausea, constipation, or abdominal discomfort

• Headache or fatigue

• Dry mouth or increased thirst

Serious adverse effects are uncommon but require immediate medical attention. Hypercalcaemia (elevated blood calcium) is the primary concern with vitamin D toxicity and may manifest as:

• Persistent nausea and vomiting

• Excessive thirst and frequent urination

• Confusion, drowsiness, or weakness

• Kidney stones or impaired kidney function

• Cardiac arrhythmias in severe cases

If you experience symptoms suggestive of hypercalcaemia, stop taking ergocalciferol immediately and seek urgent medical advice.

Contraindications and precautions: Ergocalciferol should be used with caution in patients with hypercalcaemia, hypercalciuria, kidney stones, or renal impairment. In severe chronic kidney disease, specialist advice should be sought as active vitamin D analogues (such as alfacalcidol or calcitriol) may be preferred. Patients with sarcoidosis or other granulomatous diseases may be at increased risk of hypercalcaemia due to unregulated vitamin D activation. Those with malabsorption syndromes may require adjusted dosing or alternative formulations.

Some ergocalciferol preparations contain peanut or soya oil, which may cause allergic reactions in susceptible individuals.

When to contact your GP or seek medical advice:

• If you experience symptoms suggestive of high calcium levels

• If you develop persistent side effects that concern you

• Before taking ergocalciferol if you are pregnant, breastfeeding, or planning pregnancy

• If you have existing kidney, liver, or heart conditions

If you suspect you have experienced a side effect from ergocalciferol, you can report it via the MHRA Yellow Card Scheme at www.mhra.gov.uk/yellowcard or search for 'MHRA Yellow Card' in the Google Play or Apple App Store.

When Is Ergocalciferol Prescribed in the UK?

In the UK, vitamin D supplementation is widely recommended, with cholecalciferol (vitamin D3) generally preferred as first-line therapy. Ergocalciferol (vitamin D2) may be prescribed as an alternative, particularly for those requiring a plant-based option, though vegan-suitable vitamin D3 products are now also available.

The UK government recommends that everyone should consider taking a daily supplement containing 10 micrograms (400 IU) of vitamin D during autumn and winter months. Certain at-risk groups are advised to take this supplement year-round.

Clinical indications for ergocalciferol prescription include:

• Confirmed vitamin D deficiency: Serum 25-hydroxyvitamin D levels below 25 nmol/L, often accompanied by symptoms such as bone pain, muscle weakness, or fatigue

• Osteomalacia: Softening of bones in adults due to prolonged vitamin D deficiency, presenting with bone pain and increased fracture risk

• Rickets prevention and treatment: In children, though this typically requires specialist paediatric input for appropriate dosing

• Malabsorption disorders: Conditions such as coeliac disease, Crohn's disease, or cystic fibrosis that impair vitamin D absorption

• Chronic kidney disease: Where vitamin D metabolism is impaired, though specialist advice should be sought and active vitamin D analogues may be preferred in advanced disease

At-risk groups who may be offered vitamin D supplementation include individuals with limited sun exposure (housebound or institutionalised patients), those with darker skin pigmentation living in northern latitudes, people covering their skin for cultural or religious reasons, and individuals following strict vegan diets.

GPs may prescribe ergocalciferol following blood test confirmation of deficiency, taking into account patient preferences, dietary requirements, and clinical presentation. Treatment duration typically involves an initial loading phase followed by long-term maintenance therapy, with periodic monitoring to ensure adequate vitamin D status is achieved and maintained without causing toxicity.

Frequently Asked Questions