Should I take vitamin D or D3 daily? This is a common question, particularly in the UK where limited sunlight during autumn and winter months restricts natural vitamin D synthesis. Vitamin D3 (cholecalciferol) is the form naturally produced in human skin and is generally more effective at raising blood levels than vitamin D2 (ergocalciferol). UK health authorities recommend that everyone consider taking a daily supplement of 10 micrograms (400 IU) during darker months, with certain groups advised to supplement year-round. This article explains the differences between vitamin D forms, who should take daily supplements, recommended doses, and how to choose an appropriate product.

Understanding Vitamin D and Vitamin D3: What's the Difference?

Vitamin D is a fat-soluble vitamin essential for maintaining healthy bones, teeth, and muscles. When people refer to 'vitamin D', they are typically discussing one of two forms: vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol). Understanding the distinction between these forms can help you make informed decisions about supplementation.

Vitamin D3 (cholecalciferol) is the form naturally produced in human skin when exposed to ultraviolet B (UVB) radiation from sunlight. It is also found in animal-based foods such as oily fish, eggs, and fortified foods. Vitamin D2 (ergocalciferol), by contrast, is derived from plant sources and fungi, particularly UV-irradiated mushrooms, and is sometimes used in fortified foods and certain supplements.

Once consumed or synthesised, both forms undergo a two-step conversion process: first to 25-hydroxyvitamin D in the liver (the form measured to assess vitamin D status), and then to calcitriol in the kidneys, which is the active hormone that regulates calcium absorption and bone metabolism. Research suggests that vitamin D3 is more effective at raising and maintaining blood levels of 25-hydroxyvitamin D compared to vitamin D2. According to the British National Formulary, colecalciferol (D3) is more potent and has a longer-lasting effect than ergocalciferol (D2).

For practical purposes, when choosing a supplement, vitamin D3 is generally considered the more effective option. Most over-the-counter preparations available in UK pharmacies and supermarkets contain cholecalciferol (D3). While both forms can be effective, vitamin D3 is typically the preferred form for supplementation due to its greater bioefficacy.

Who Should Take Vitamin D Daily in the UK?

The UK's geographical location—between 50° and 60° north latitude—means that sunlight intensity is insufficient to stimulate adequate vitamin D synthesis in the skin for much of the year, particularly from October through March. Consequently, UK health authorities advise that everyone should consider taking a daily vitamin D supplement of 10 micrograms (400 IU) during the autumn and winter months.

Certain groups are at higher risk of vitamin D deficiency and should take a daily supplement of 10 micrograms throughout the entire year. These include:

• Individuals with limited sun exposure: Those who are housebound, live in care homes, or habitually cover their skin for cultural or religious reasons

• People with darker skin tones: Higher melanin levels reduce the skin's ability to produce vitamin D from sunlight; individuals of African, African-Caribbean, or South Asian heritage are particularly at risk

• Older adults: Skin synthesis of vitamin D declines with age, and older people may spend less time outdoors

• Infants and young children: Breastfed babies from birth to one year should receive a daily supplement, as breast milk contains limited vitamin D

• Pregnant and breastfeeding women: To support foetal skeletal development and maternal bone health

• People with obesity: Those with a BMI of 30 kg/m² or above may require higher doses under medical supervision

Additionally, people with malabsorption disorders (such as coeliac disease, Crohn's disease, or cystic fibrosis) or those taking certain medications (including some anticonvulsants and corticosteroids) may require higher doses under medical supervision. Eligible pregnant women, breastfeeding mothers and young children can access free Healthy Start vitamins containing vitamin D. If you fall into any of these categories, it is advisable to discuss supplementation with your GP or a registered dietitian to ensure your vitamin D intake is adequate and safe.

Recommended Daily Doses and NHS Guidelines

The UK government recommends a daily intake of 10 micrograms (400 IU) of vitamin D for the general population, including pregnant and breastfeeding women. This recommendation is based on evidence reviewed by the Scientific Advisory Committee on Nutrition (SACN) and is designed to maintain bone and muscle health in the majority of people.

For infants from birth to one year, the NHS advises a daily supplement of 8.5 to 10 micrograms of vitamin D, particularly if they are breastfed or consuming less than 500ml of infant formula per day (as formula is already fortified). Children aged one to four years should receive a daily supplement of 10 micrograms, available through the Healthy Start scheme for eligible families.

It is important to note that these are maintenance doses for individuals with normal vitamin D status. Those diagnosed with vitamin D deficiency (serum 25-hydroxyvitamin D levels below 25 nmol/L) may require higher therapeutic doses, often in the range of 20,000 to 50,000 IU weekly for a limited period, followed by maintenance therapy of 800-2000 IU daily (occasionally up to 4000 IU under supervision). Such treatment should only be initiated and monitored by a healthcare professional. Routine testing for vitamin D status is not generally recommended for asymptomatic people; the standard 10 microgram daily dose can be taken safely without testing.

Upper safe limits have been established to prevent toxicity. For adults and children aged 11-17 years, the tolerable upper intake level is 100 micrograms (4,000 IU) per day. For children aged 1-10 years, the upper limit is 50 micrograms (2,000 IU) per day, and for infants under 1 year, it is 25 micrograms (1,000 IU) per day. Exceeding these amounts over prolonged periods can lead to hypercalcaemia, resulting in nausea, weakness, kidney stones, and, in severe cases, cardiac arrhythmias. Always adhere to recommended doses unless otherwise directed by your doctor, and avoid taking multiple supplements that contain vitamin D simultaneously to prevent inadvertent overdose.

Benefits and Risks of Daily Vitamin D Supplementation

Benefits of maintaining adequate vitamin D levels are well-established and primarily relate to musculoskeletal health. Vitamin D facilitates intestinal absorption of calcium and phosphate, which are critical for bone mineralisation. Deficiency in children can lead to rickets, characterised by soft, weak bones and skeletal deformities. In adults, inadequate vitamin D contributes to osteomalacia (bone softening) and may increase the risk of falls and fractures, particularly in older adults. Vitamin D supplementation alone has limited effect on fracture prevention in community-dwelling adults, but may be beneficial when combined with calcium in certain high-risk groups.

Research has explored potential roles of vitamin D in immune function, cardiovascular health, and mood regulation. Some observational studies have suggested associations between low vitamin D levels and increased susceptibility to respiratory infections, autoimmune conditions, and depression. However, UK reviews by SACN and NICE have concluded there is insufficient evidence to recommend routine supplementation specifically for these non-skeletal outcomes. The primary reason for taking vitamin D remains the maintenance of bone and muscle health.

Risks associated with daily vitamin D supplementation are minimal when taken at recommended doses. Vitamin D toxicity is rare and typically occurs only with excessive supplementation (well above 4,000 IU daily over extended periods). Symptoms of toxicity include hypercalcaemia, which may present as nausea, vomiting, constipation, confusion, and in severe cases, renal impairment.

Certain individuals should exercise caution: those with sarcoidosis, primary hyperparathyroidism, kidney disease, or a history of recurrent kidney stones may be more susceptible to hypercalcaemia and should only take vitamin D under medical supervision. Additionally, vitamin D can interact with medications such as thiazide diuretics, digoxin, orlistat, bile acid sequestrants (cholestyramine), rifampicin, and enzyme-inducing antiepileptics, potentially affecting either vitamin D levels or increasing the risk of adverse effects. Always inform your GP or pharmacist of all supplements and medications you are taking.

When to Take Vitamin D3 and How to Choose a Supplement

Timing of supplementation can influence absorption, though the effect is modest. Because vitamin D is fat-soluble, taking your supplement with a meal containing some dietary fat may enhance absorption. There is no evidence favouring morning versus evening dosing, so choose a time that fits your routine and helps ensure consistency. The most important factor is daily adherence.

When selecting a vitamin D supplement, consider the following:

• Dosage: Choose a product providing 10 micrograms (400 IU) for general maintenance, unless your doctor has recommended a higher dose

• Form: Tablets, capsules, oral sprays, and liquid drops are all effective; choose based on personal preference and ease of use

• Quality assurance: For high-dose treatment, look for MHRA-licensed medicines (with a PL number). For standard food supplements, buy from reputable UK retailers and check for compliant labelling (marked as a 'food supplement', with clear dosage information, ingredients list, and manufacturer details)

• Vegetarian and vegan options: Standard vitamin D3 is derived from lanolin (sheep's wool), but vegan D3 sourced from lichen is available for those following plant-based diets

• Combination supplements: Some multivitamins include vitamin D; check the label to avoid duplication and ensure you are not exceeding safe limits

When to contact your GP: Routine vitamin D testing is not recommended for asymptomatic people; the standard 10 microgram daily dose can be taken safely without testing. However, if you experience symptoms suggestive of deficiency (persistent fatigue, bone pain, muscle weakness, frequent infections) or have risk factors for deficiency, discuss with your GP whether a blood test to assess your vitamin D status is appropriate. Similarly, if you develop symptoms of toxicity after supplementation (nausea, excessive thirst, confusion), seek medical advice promptly. Your GP can provide personalised guidance and, if necessary, prescribe higher-dose preparations for therapeutic use.

If you experience side effects from a licensed vitamin D medicine, report them through the MHRA Yellow Card Scheme, which helps monitor the safety of medicines in the UK.

Frequently Asked Questions