When to take vitamin D in a UK winter

When should you start taking vitamin D in the UK?

October, and keep going until the end of March. From about late March or early April to the end of September, most people in the UK can make all the vitamin D they need from sunlight on their skin. From October to early March they can't. The Scientific Advisory Committee on Nutrition (SACN) explains why: UK winter sunlight carries so little UVB, the part of sunlight skin needs, that vitamin D production is negligible from at least October through early March.

So the NHS advises that everyone, including pregnant and breastfeeding women, should consider a daily supplement containing 10 micrograms (µg) of vitamin D during autumn and winter.

The winter dip shows up in blood tests. In the national survey data SACN reviewed for its 2016 report, around 30 to 40% of people had blood levels below 25 nmol/L in winter, against 2 to 13% in summer. SACN treats 25 nmol/L as the level below which the risk to bone and muscle health goes up, and it set 10 µg a day as the amount that would keep almost everyone above it through the winter.

What are the benefits of vitamin D?

The NHS says vitamin D helps regulate the amount of calcium and phosphate in the body, and that those minerals keep your bones, teeth and muscles healthy. The British Dietetic Association describes the same job as helping your body take in calcium and phosphorus.

The benefit shows most clearly when it's missing. The NHS says a lack of vitamin D can lead to bone deformities such as rickets in children, and to bone pain from osteomalacia in adults. That is why the advice is about getting enough rather than taking more: the NHS puts the amount most people need at 10 µg (400 IU) a day, and the British Dietetic Association says much larger amounts are unnecessary and can be harmful. The signs of low vitamin D are covered further down.

Who should take vitamin D all year round?

The NHS suggests taking 10 µg a day all year round if you:

• are not often outdoors, for example because you're frail or housebound
• live in a care home or similar setting
• usually wear clothes that cover most of your skin when you're outside
• have dark skin, for example if you're from an African, African-Caribbean or south Asian background, because you may not make enough vitamin D from sunlight even in summer

Babies and children have their own advice, set out in the next section.

How much vitamin D do babies and kids need?

Babies up to 1 year need 8.5 to 10 µg a day (about 340 to 400 IU) if they are breastfed, or if they have less than 500 ml of infant formula a day. Formula already has vitamin D added, so a baby having more than 500 ml a day shouldn't be given a supplement. Children aged 1 to 4 need 10 µg (400 IU) a day all year round.

From age 5 the advice matches the adult advice: consider 10 µg a day in autumn and winter, and all year if you're in one of the groups above. Vitamin drops for under 5s are sold at most pharmacies and supermarkets, and families who qualify for Healthy Start can get them free. Don't give a child cod liver oil and vitamin drops together, because cod liver oil also contains vitamins A and D. The upper limits are 25 µg (1,000 IU) a day under 12 months and 50 µg (2,000 IU) from 1 to 10 years. The NHS guide to vitamins for children has the detail.

How much vitamin D should you take, in µg and IU?

For most adults, 10 µg a day. The confusion comes from labels, which use two different units. UK guidance uses micrograms, written µg or mcg. Many products, especially imported ones, use international units (IU). One microgram is 40 IU.

So a "vitamin D 1000 IU" tablet is 25 µg, two and a half times the NHS amount. That's within the safe limit for adults, but it's more than the guidance asks for. If your GP has recommended a different dose for you, follow that instead. To convert any other amount, use our vitamin unit converter.

If you're comparing vitamin D tablets, check the form (D3, see below), the dose (10 µg covers the NHS advice) and whether a multivitamin or another supplement you take already contains vitamin D, because the amounts add up.

Is vitamin D 1000 IU, 2000 IU or 4000 IU too much?

None of them goes above the NHS adult upper limit of 100 µg (4,000 IU) a day, but only 400 IU (10 µg) is the amount the NHS advises for most people. Labels use different units, which is why the same amounts look so different:

• 1,000 IU (25 µg, sometimes printed 25ug or 25 mcg): two and a half times the NHS amount.
• 2,000 IU (50 µg): five times the NHS amount and half the adult limit. It equals the upper limit for children aged 1 to 10.
• 4,000 IU (100 µg): exactly the adult limit. Treat it as a ceiling rather than a target, and count any vitamin D in a multivitamin towards it.

"High strength" on a label isn't a dose, so look for the µg or IU in each tablet and compare it with these figures. If your GP has told you to take a different amount, follow that. To convert any other figure, use our vitamin unit converter.

Can you have too much vitamin D?

Yes, from supplements. The NHS says adults and children aged 11 to 17 should not take more than 100 µg (4,000 IU) a day, because it could be harmful. The limit is 50 µg for children aged 1 to 10, and 25 µg for babies under 12 months. You can't overdose on vitamin D from sunlight, though strong sun brings its own risks to your skin.

Taking too much over a long period can make calcium build up in the body, a condition called hypercalcaemia. That can weaken the bones and damage the kidneys and the heart. A 2018 clinical review lists confusion, apathy, repeated vomiting, abdominal pain, peeing a lot and being very thirsty among the symptoms most often noted. It calls toxicity rare, puts acute toxicity at doses probably above 10,000 IU a day, and says daily doses above 4,000 IU taken for long periods could cause chronic toxicity (Marcinowska-Suchowierska and colleagues).

The NHS also points out that some people have medical conditions that mean they may not be able to take as much safely. If you have a long-term condition or take regular medicines, ask your GP or pharmacist before you start, and speak to your GP or call 111 if you have these symptoms while taking high-dose vitamin D.

What time of day should you take vitamin D?

Whenever you're most likely to remember. UK guidance doesn't name a best time of day, and what keeps your levels up over winter is taking it most days. Pairing it with something you already do each morning or evening makes that easier.

Taking it with a meal may help a little. Vitamin D is fat-soluble, and in a trial of 50 older adults given a single large dose (50,000 IU), blood vitamin D3 peaked 32% higher when the dose came with a meal containing fat than with a fat-free one. That was one big dose rather than a daily 10 µg, so it doesn't tell us how much a meal matters at everyday amounts. Taking it with breakfast or dinner is still an easy habit to keep. If you take magnesium as well, our guide to magnesium glycinate vs citrate covers forms and timing.

Vitamin D spray, gummies, liquid or tablets: does the format matter?

Few trials compare formats head to head, so the label matters more than the shape. In a 2021 randomised trial of 90 children and teenagers with low vitamin D, a buccal spray and oral drops raised blood levels by similar amounts (Nalbantoğlu and colleagues). A 2025 trial in 120 people with inflammatory bowel disease found similar rises from an oral spray and an oil-based emulsion (Kojecký and colleagues). Both groups had low levels or gut disease, so the results may not carry over to a healthy adult. We found no trial of standard gummies against tablets.

Whatever you choose, check:

• the µg or IU in one dose, and how many sprays, gummies or drops make up that dose
• the form, D3 or D2
• the sugar in a gummy: the NHS says adults should have no more than 30 g of free sugars a day, and that sugar is one of the main causes of tooth decay
• whether a multivitamin already gives you vitamin D, because the amounts add up

What's the difference between vitamin D and vitamin D3?

Vitamin D is the name for the nutrient, and D3 is one of its two supplement forms. A tablet labelled "vitamin D" contains either D3 (cholecalciferol) or D2 (ergocalciferol), and "vitamin D3 tablets" simply say which. The NHS advice is for 10 µg of vitamin D a day and doesn't distinguish between the forms.

Vitamin D3 or D2: which should you choose?

D3 raises blood levels more reliably. D3 (cholecalciferol) is the form your skin makes; D2 (ergocalciferol) comes from fungi and yeast. A 2012 meta-analysis found D3 raised blood levels more than D2, with the clearest difference when people took large, infrequent doses. A 2017 UK trial then tested everyday amounts: 335 women took 15 µg a day of one form or the other, in juice or a biscuit, for 12 weeks over winter, and D3 raised blood levels significantly more than D2. The British Dietetic Association calls D3 the most effective form and describes D2 as a plant-based alternative.

Is there a vegan vitamin D?

Yes. The British Dietetic Association says vitamin D2 is a plant-based alternative suitable for vegetarians and vegans. Making D3 involves lanolin from sheep's wool, according to a 2023 review of animal-derived ingredients in medicines (Silk and colleagues), so a vegan D3 needs another source. Vitamin D3 also occurs in some lichens: a 2001 laboratory study identified it in the lichen Cladina arbuscula (Wang and colleagues). A supplement that uses a lichen source will say so on the label.

Does the form matter? A 2026 review concluded that D2 is often less effective than D3 at raising total blood vitamin D, but also noted that several trials found the two comparable at low daily doses (Bieg and colleagues). If you avoid animal products, look for D2 or for a D3 whose label names a non-animal source, and compare the µg per dose with the figures above.

Can you get enough vitamin D from food?

Rarely. Few foods contain much: oily fish such as salmon, sardines, trout, herring and mackerel, red meat, egg yolks, liver, and fortified foods such as some fat spreads and breakfast cereals. The British Dietetic Association says even a well-balanced diet is unlikely to give you enough on its own. In the survey data behind SACN's report, average intakes from all sources, supplements included, were about 2 to 4 µg a day for people aged 18 months to 64 years, well short of 10 µg. Food still counts towards your total; it just won't close the winter gap by itself.

What are the symptoms of low vitamin D, and should you get tested?

Long-term low vitamin D can soften the bones, which in adults is called osteomalacia. The NHS lists pain in the back, shoulders, ribs, pelvis or legs, and weak muscles that make it hard to climb stairs or get up from a chair. Lists online often add vaguer symptoms like tiredness, which has many possible causes.

A blood test isn't routine. NICE advises health professionals not to test vitamin D levels unless someone has symptoms of deficiency, is at particularly high risk (for example, they get very little sun), or there's another clinical reason, such as osteomalacia or a fall. If you have bone pain, muscle weakness or several of the risk factors above, see your GP rather than treating yourself with high-dose tablets.

Should you take vitamin D3 with K2?

You don't need to, and if you take warfarin you shouldn't start K2 without medical advice. Vitamin K is a separate nutrient. In Great Britain it is authorised to say two things: it contributes to normal blood clotting and to the maintenance of normal bones. Most people get enough from food, such as green leafy vegetables like broccoli and spinach, vegetable oils and cereal grains. The NHS puts adult needs at about 1 µg per kilogram of body weight a day.

The case for pairing them is that both have a role in bone. The evidence that the combination does more than vitamin D alone is limited. A 2019 systematic review of 36 trials of vitamin K found no evidence that it changes bone density or spinal fractures in postmenopausal women or people with osteoporosis, and judged the evidence on other fractures too weak to confirm a benefit. A 2026 analysis from the US VITAL trial, in 771 adults, found that people with higher vitamin K levels got no extra bone benefit from vitamin D supplements. That study measured vitamin K in the blood rather than testing K2 tablets. Our guide to vitamin D3 and K2 covers the research, food sources and timing in more detail.

If you're in perimenopause and thinking about your bones more broadly, our guide to perimenopause supplements covers what calcium and vitamin D are authorised to say for women after the menopause.

Where Natura fits

Daily D3, in the Natura cabinet (coming soon), is vitamin D3 from lichen at 10 µg (400 IU), the amount the NHS suggests for autumn and winter. Vitamin D contributes to the maintenance of normal bones and normal muscle function, and to the normal function of the immune system. Daily K2 (vitamin K2 as MK-7, 75 µg) is a separate bottle rather than a combined D3 and K2 product. If you take warfarin or another blood thinner, check with your pharmacist or anticoagulation clinic before starting either. Both are listed with the daily bottles.