Vitamin D is unusual among nutrients in having its own seasonal public health advice in the UK, and it is the one supplement that official guidance suggests most of the population should consider. That is a function of latitude rather than diet. Between roughly October and early March, sunlight over Britain does not contain enough UVB for the skin to make vitamin D at all, however long you spend outside.
The guidance itself is short and specific. What tends to confuse people is everything around it: two different units on the label, wildly varying strengths on the shelf, the difference between a general recommendation and treatment for a diagnosed deficiency, and the question of how much is too much. This guide works through each of those in turn.
Why the UK has seasonal vitamin D advice
Most vitamin D is not obtained from food. It is made in the skin when UVB radiation reaches it, and the amount of UVB in sunlight depends on the angle of the sun. Britain sits far enough north that from around October to early March the sun does not climb high enough for meaningful UVB to get through the atmosphere. During those months, time outdoors does not contribute to vitamin D status regardless of how bright the day looks.
That is why the advice is framed seasonally rather than as a year-round recommendation for everyone. It is also why it is population-level advice: it is designed to cover nutritional need across a whole country during the months when the usual source is unavailable, not to correct a problem in a particular individual.
The 10 microgram recommendation and who it is for
UK guidance advises that adults and children over the age of four should consider taking a daily supplement containing 10 micrograms of vitamin D during autumn and winter. Public Health England and NICE have issued a joint statement to that effect, and the NHS repeats it on its vitamin D page.
Two words in that sentence do a lot of work. Consider signals that this is advice to weigh rather than an instruction, and 10 micrograms is a figure aimed at maintaining adequate status across the general population. It is not a dose scaled to your body weight, your diet, your skin tone or your blood test result.
Separate advice applies to babies and young children, and to pregnancy and breastfeeding. The NHS Healthy Start scheme provides vitamin supplements to some families. If you are looking for advice for a child under four, use the NHS page rather than a supplement label, and speak to a health visitor or GP.
Who is advised to supplement all year round
Some people are unlikely to make enough vitamin D even in summer, and government guidance advises those groups to consider 10 micrograms daily throughout the year rather than only in the darker months.
- People who are rarely outdoors, including those who are frail or housebound.
- People living in a care home.
- People who usually wear clothing that covers most of their skin when outdoors.
- People from African, African-Caribbean and South Asian backgrounds, who may not make as much vitamin D from sunlight.
If you fall into one of these groups, that is the relevant guidance for you, and it is worth mentioning at your next appointment rather than managing entirely from the shelf. The same is true if you have a condition affecting fat absorption, since vitamin D is fat-soluble and absorption can be affected.
Micrograms, IU and reading the number correctly
Vitamin D labels use two units, sometimes both at once, and the arithmetic catches people out. One microgram of vitamin D equals 40 international units. The conversions worth memorising are these: 10 µg is 400 IU, 25 µg is 1,000 IU, 50 µg is 2,000 IU, and 100 µg is 4,000 IU.
UK panels state the microgram figure and the %NRV, and often print the IU figure in brackets. Our Vitamin D3+K2 Advanced panel reads 50 µg (2,000 IU) at 1000% of the NRV for a two-capsule serving. Our Complete Daily Multivitamin reads 25 µg (1,000 IU) at 500% for a one-capsule serving.
A 1000% figure looks alarming until you notice that the reference value it is measured against is 5 µg, which is low relative to the 10 µg the UK actually advises. That is exactly why the percentage should be read as a comparison device and not as a safety indicator.
Deficiency is a diagnosis, not a self-assessment
Vitamin D deficiency is a clinical diagnosis made on the basis of a blood test, usually of 25-hydroxyvitamin D, interpreted alongside your history and symptoms. The symptoms people associate with it — tiredness, aching, low mood, general run-down feeling — are non-specific and overlap with a long list of other things, some of which matter a great deal.
That is the practical reason not to self-diagnose from a symptom list on the internet. If you feel persistently unwell, the useful step is a GP appointment where vitamin D can be considered alongside everything else, not a higher-strength bottle bought on the assumption that vitamin D is the answer.
Where deficiency is confirmed, it is treated on medical advice, often at doses and schedules quite different from general retail guidance. Retail supplements are for nutritional maintenance. Follow your prescriber rather than a label if the two ever appear to disagree.
How much is too much
Vitamin D is fat-soluble, which means it accumulates rather than being cleared quickly like vitamin C. Too much over a long period can raise blood calcium, and that can cause real harm. This is not a nutrient where more is quietly better.
The NHS publishes guidance on upper intakes for adults, and it is worth reading rather than paraphrasing from a product page. The important habit is to count every source: a multivitamin, a standalone vitamin D, a combination product like ours, a cod liver oil, and anything prescribed. Our multivitamin and our D3+K2 formula together would supply 75 µg a day, which is a decision to make on purpose.
Some people should take particular care and get advice before starting any vitamin D supplement: anyone with a calcium disorder such as hypercalcaemia, kidney disease, sarcoidosis or another granulomatous condition, and anyone taking medicines where vitamin D or calcium is relevant. Our own label carries that caution for exactly this reason.
Food sources and why they rarely close the gap
A small number of foods contain useful amounts of vitamin D: oily fish such as salmon, mackerel, sardines and herring, egg yolks, liver, and foods that have been fortified, including many breakfast cereals and fat spreads. Mushrooms exposed to ultraviolet light contain vitamin D2.
The difficulty is quantity. Reaching 10 micrograms a day from food alone requires eating oily fish regularly and paying attention to fortified products, which is achievable for some people and unrealistic for many, particularly on a vegan or vegetarian diet. That gap between what is theoretically possible and what people actually eat is the reason the national advice exists in the first place.
None of this makes food irrelevant. A supplement is there to fill a specific seasonal gap, not to replace a varied and balanced diet, and UK labelling rules require every food supplement to say so.
Reading a vitamin D label
Vitamin D products vary more widely in strength than almost any other category on the shelf, so the label check matters here more than most.
- Which unit? Find the microgram figure, and convert any IU figure by dividing by 40.
- Which serving? Check whether the amount is per capsule or per two, and count the servings per bottle rather than the capsules.
- D2 or D3? D3 is cholecalciferol; D2 is ergocalciferol. Vegan D3 products exist and are usually lichen-derived, so check the source if that matters to you.
- What else is in it? Combination products may add vitamin K, calcium or other ingredients, each with its own cautions.
- What do the warnings say? Read them before you buy rather than after, particularly if you take any prescribed medicine.
Frequently asked questions
How much vitamin D should I take a day in the UK?
UK guidance advises adults and children over four to consider a daily supplement containing 10 micrograms — 400 IU — during autumn and winter, and some groups are advised to consider the same amount all year. That is general population advice for nutritional maintenance. If you have been told you are deficient, or you have a condition affecting calcium or the kidneys, follow medical advice instead.
Can I get enough vitamin D from sunlight in the UK?
From late March to the end of September most people can make enough from short daily periods outdoors with forearms, hands or lower legs uncovered. From October to early March there is not enough UVB in UK sunlight for the skin to make any, regardless of how long you spend outside or how bright the day is.
Is 4,000 IU of vitamin D too much?
4,000 IU is 100 micrograms, which is ten times the amount UK guidance suggests considering. Products at that strength are sold, but taking one is a decision worth discussing with a pharmacist or GP, especially alongside a multivitamin that already contains vitamin D. The NHS publishes guidance on upper intakes, and vitamin D accumulates in a way that water-soluble vitamins do not.
Should I take vitamin D with food?
Vitamin D is fat-soluble, so it is generally taken with a meal that contains some fat. Our own label directs a two-capsule serving with a meal for that reason. Beyond that, consistency matters more than timing — the same time each day is easier to remember than an optimal one.
Before choosing a supplement
- Read the complete current label, including the active and the other ingredients.
- Compare the daily serving rather than the number printed on the front of the bottle.
- Add up every source of the same nutrient across your whole routine.
- Ask a pharmacist or qualified healthcare professional about medicines, pregnancy, breastfeeding, surgery or an existing condition.
- Remember that food supplements do not replace a varied, balanced diet and a healthy lifestyle.
Related guides on this formula
- Vitamin D3 and K2 on one label: what MK-7 and PEA are doing there
- A UK winter wellbeing checklist that stays realistic
View the Vitamin D3+K2 Advanced label, the full ingredient panel and current purchase options.
Also useful: RevaHealth Journal · full range · Ingredients · Contact.
References and further reading
- NHS: Vitamin D
- GOV.UK: PHE and NICE statement on vitamin D supplementation during winter
- GOV.UK: SACN vitamin D and health report
This article is general educational information, not medical advice. Food supplements are not medicines and are not intended to diagnose, treat, cure or prevent disease. Always read the complete physical label before use, and speak to your GP or pharmacist if you are unsure whether a supplement is right for you.
