Vitamin D is unusual: your skin can make it when sunlight reaches it, yet during the UK autumn and winter, sunlight is not strong enough to provide what you need. That makes vitamin D worth thinking about even if you spend time outdoors and eat a varied diet. [2] [6]
Vitamin D
Helps your body use calcium
Options to consider
- Fortified drinks
- UV-exposed mushrooms
- Suitable supplement
Plan vitamin D separately from how many vegetables you eat. See the UK advice below.
Sources [21] [1]It helps your body absorb calcium and regulate phosphate, supporting healthy bones, teeth and muscles. This matters whatever you eat. If you are plant-based, there are suitable supplements and some useful food sources, but checking the details helps. [1] [6]
I would start with a few practical questions: when do you need a supplement, what does the amount on the label mean, and is the product suitable for you? You can work through those without needing to become an expert in every vitamin D claim you come across.
Why does vitamin D matter?
Vitamin D helps your body use calcium to keep bones strong. Too little can lead to rickets in children or osteomalacia in adults, where bones become soft. It also has a role in normal immune function. [2]
Supporting a normal body function is different from promising that extra vitamin D will prevent illness. The Vegan Society makes this distinction in its guidance: vitamin D supports the immune system, but it should not be treated as a supplement that can protect against or treat infection on its own. [5]
It belongs alongside the other parts of your nutrition plan. If calcium is something you are working through too, the calcium guide explains food sources and portions.
Can I get enough vitamin D from sunlight?
During spring and summer, many people in the UK can make enough vitamin D from sunlight. Autumn and winter bring a seasonal gap, so being outdoors regularly does not remove the need to think about supplements. [4] [6]
There is no single number of minutes that works for everyone. Skin tone, the time of day and the season affect vitamin D production. You do not need to sunbathe or get a tan. Enjoy time outside while protecting your skin from burning; extra unprotected exposure is not a dependable supplement plan. [4]
Cancer Research UK puts it plainly:
“you don’t need to sunbathe to get enough vitamin D.”
Cancer Research UK, Sun and vitamin D [4]
Sunlight through a window does not count in the same way. Glass blocks the UVB rays needed for vitamin D production in skin, so sitting beside a sunny window does not provide that source. [2]
How much vitamin D should I consider in the UK?
For UK adults, consider a daily supplement containing 10 micrograms of vitamin D during autumn and winter. Some people need to consider supplementation throughout the year, including those who rarely go outdoors, cover most of their skin outside or have darker skin. [1]
The UK's scientific advisory recommendation is a daily intake of 10 micrograms from dietary sources, including fortified foods and supplements, to protect muscle and bone health. That reference intake was developed without assuming a particular amount of sunlight exposure, because skin production varies so much. [3]
Plant-Based Health Professionals UK's vitamin D factsheet, written by pharmacist Sheetal Ladva Kanwar, also explains the 10-microgram seasonal recommendation and the groups who need year-round attention. A plant-based approach still includes planning for vitamin D. [6]
What do micrograms and IU mean?
Micrograms may be written as mcg or µg. IU stands for International Units, another way to express the amount of vitamin D. One microgram equals 40 IU, so 10 micrograms is 400 IU. These are two labels for the same amount, not different strengths. [6]
I would check that conversion before comparing products. Look at the amount per tablet, drop or serving, as well as how often the instructions say to take it. A larger number on the front of a bottle does not establish that it is the right choice for you.
Pregnancy, breastfeeding and children's needs deserve their own advice. Speak with your midwife, health visitor or pharmacist about an appropriate product and dose. In particular, do not assume an adult tablet or dropper is suitable for a baby. The age-specific guidance includes how infant formula affects the need for supplements. [1]
What is the difference between vitamin D2 and D3?
The two main forms in foods and supplements are D2, called ergocalciferol, and D3, called cholecalciferol or colecalciferol. Both can contribute to vitamin D status. D2 is not animal-derived; D3 may come from lanolin in sheep's wool, or from a vegan source such as lichen. Check the product rather than assuming all D3 is suitable. [5] [6]
The capsule ingredients matter too. A vegan source of the vitamin does not necessarily mean the whole product is vegan. Look for clear vegan labelling or confirmation from the manufacturer. The PBHP UK factsheet notes that formulations can change, so an old product list is not a permanent guarantee. [6]
Is D3 better than D2?
A UK randomised trial by Laura Tripkovic and colleagues studied 335 healthy South Asian and white European women during winter. Participants received a placebo or 15 micrograms daily of D2 or D3 in juice or biscuits for 12 weeks. D3 raised total blood 25-hydroxyvitamin D, the usual marker of vitamin D status, more than D2. [7]
The researchers concluded that:
“vitamin D3 was more effective than vitamin D2 in increasing serum 25(OH)D in the wintertime.”
Tripkovic and colleagues, American Journal of Clinical Nutrition [7]
This is useful evidence when comparing forms. It does not show that D2 is useless, or that choosing D3 automatically prevents more fractures or other illnesses. The study measured blood levels over a short period in women, rather than long-term health outcomes in everyone. A suitable vegan D3 product is an option, but keep the dose and your circumstances in view too. [7]
An earlier review by Tripkovic and colleagues pooled trials comparing D2 and D3. D3 raised blood vitamin D more overall, although the difference was not statistically clear in the daily-dose subgroup of that 2012 review. A separate 2017 trial by Hammami and Yusuf found that responses also depended on the dosing schedule and sex. Both help explain why studies can reach different results when they use different routines. [13] [14]
Which plant-based foods provide vitamin D?
Useful options include foods with vitamin D added and mushrooms exposed to UV light to increase their D2 content. Mushroom vitamin D content varies. Ordinary vegetables, nuts and seeds should not be counted on to supply enough simply because they contribute other nutrients. [2]
Check vitamin D specifically on fortified food labels; a product being plant-based, or having calcium added, does not tell you whether it also provides vitamin D. The Vegan Society notes that a varied diet, even with fortified foods, can still leave someone at risk of low vitamin D. [5] [6]
For example, you could use a vitamin D-fortified drink in porridge or choose labelled vitamin D mushrooms for a stew. I would treat those as useful additions and still follow the supplement advice appropriate to the season and your situation. The plant milk guide can help with checking cartons.
How should I take a supplement?
Vitamin D is fat-soluble. Taking it with a meal or snack containing some fat can help absorption. That could mean a meal with nuts, seeds, avocado or a nut butter; you do not need to start cooking with oil to do this. [5]
Choose a time you can remember and follow the product or prescription instructions. If you take a multivitamin, read its contents before buying another vitamin D supplement. Make a note of the amount in each product so you can ask a pharmacist to check the combination.
Check the full ingredient list for allergies as well as dietary preferences. Some preparations may be unsuitable for people with a peanut or soya allergy, and some capsules contain gelatine. A pharmacist can help you find a suitable alternative. [10]
How would I know if I need a vitamin D test?
Persistent bone discomfort or muscle weakness deserves a conversation with your GP. Vitamin D deficiency can contribute to muscle and bone problems, but symptoms need assessment rather than a diagnosis based on how you feel after reading an article. [9]
Routine testing is not recommended for everyone. NICE advises testing when someone has symptoms of deficiency, is at particularly high risk or has a clinical reason for a test. You do not generally need to arrange a blood test just to follow routine seasonal supplement advice. [8]
If deficiency is diagnosed, a clinician may prescribe a short course of a higher dose, sometimes called a loading dose, followed by an ongoing plan. That is treatment for an identified problem. It should not be copied from another person's prescription or replaced with a general dose from a website. [9]
Does taking extra vitamin D prevent fractures?
More vitamin D does not automatically mean stronger bones. In the VITAL fracture study, 25,871 generally healthy US adults received 2,000 IU of D3 daily or placebo. Over a median 5.3 years, the supplement did not significantly reduce total, hip or other nonvertebral fractures. [12]
The participants were not selected because they had vitamin D deficiency, osteoporosis or low bone mass. This is important: the result does not mean that diagnosed deficiency should go untreated. It also does not establish that everyone benefits from taking a dose above routine guidance. The participants, starting levels and outcomes measured all affect what a trial can tell you. [12]
A broader Cochrane review from 2014 adds another part of the picture. Across studies in older people, vitamin D alone did not prevent fractures in the regimens tested, while vitamin D combined with calcium gave a small reduction in hip fractures. That combination and the people studied differ from the VITAL trial above, so I would keep both in mind when reading a headline about bone health. Your own food intake and treatment needs still matter when deciding whether to add calcium. [18]
What about cancer and living longer?
A 2014 Cochrane review found a possible reduction in deaths with D3, mostly in older people, but missing results and people dropping out of trials limited confidence. A separate review that year found no reduction in the number of people developing cancer, while possible effects on deaths remained uncertain. [15] [17]
The later VITAL trial followed 25,871 adults for a median of 5.3 years. Taking 2,000 IU of D3 each day did not significantly reduce invasive cancer, major cardiovascular events or deaths from any cause. I would use these findings to keep expectations realistic when choosing a supplement. Meeting your vitamin D needs remains worthwhile; extra tablets cannot be promised to prevent these illnesses. [20]
Why is there research on vitamin D and liver disease?
This is a separate treatment question for people with a diagnosed condition. The 2017 Cochrane review has a 2021 update covering 27 trials. The updated evidence was too uncertain to establish whether supplementation improved important outcomes in chronic liver disease. If this affects you, discuss vitamin D with your clinical team rather than using a general supplement guide as a treatment plan. [16] [19]
Can you take too much vitamin D?
Yes. Taking too much over time can cause calcium to build up in the body, which can damage the kidneys and heart. Prescribed high-dose treatment needs clinical supervision. A personal account of taking very large amounts is not evidence that the same approach is safe for someone else. [9]
For adults, the general upper limit is 100 micrograms, or 4,000 IU, a day. That is a safety limit, not a target to aim for. Some people need a lower limit because of a medical condition. Follow your clinician's instructions if you are receiving treatment. [1]
Ask before starting a supplement if you have kidney problems, a history of kidney stones, high calcium levels or sarcoidosis. [10] Medicines can also affect vitamin D use, including some epilepsy medicines, steroids, digoxin and certain diuretics. Take your medicine and supplement list to a pharmacist instead of adjusting prescribed doses yourself. [11]
A couple more practical questions
Should I add calcium to my vitamin D supplement?
Not automatically. They are separate parts of your nutrition plan. Before choosing a combined product, look at your food and any prescribed treatment, then ask whether extra calcium is appropriate. If you already take prescribed colecalciferol, check with your doctor before adding supplements containing calcium or more vitamin D. [11]
Where can I start today?
Read the label on any supplement you already use. Check the vitamin D amount, whether it suits your diet and how often you should take it. If you are unsure, take the packaging to a pharmacist. A clear routine that fits your needs is more useful than collecting several bottles with different promises.
