When Should UK Adults Start Taking Vitamin D? The NHS October to March Advice Explained

UK adults should consider taking 10 micrograms (400 IU) of vitamin D a day from October through to early March, in line with NHS advice. Between those months, UK sunlight is too weak for skin to make enough vitamin D. Some people should take it every day of the year.

The rest of this guide covers why the dates fall where they do, who shouldn't stop in spring, how much is too much, and what to check on a label so the product you buy matches the advice. It sits within NovusDNA's wider guide to foundational health, where vitamin D is one of the few supplements with clear UK public health guidance behind it.

What does the NHS say about vitamin D?

The NHS says adults need 10 micrograms of vitamin D a day and that everyone should consider a daily 10 microgram supplement during autumn and winter. In its words, "between October and early March we do not make enough vitamin D from sunlight."

The key points from the NHS vitamin D guidance:

• Daily need: 10 micrograms a day for adults and children from age 1. One microgram equals 40 IU, so 10 micrograms is 400 IU.

• Autumn and winter: everyone should consider a 10 microgram supplement.

• Spring and summer: from about late March or early April to the end of September, most people can make what they need from sunlight.

• Upper limit: adults should not take more than 100 micrograms (4,000 IU) a day.

The 10 microgram figure comes from the Scientific Advisory Committee on Nutrition (SACN). Its 2016 Vitamin D and Health report set it so that blood levels of vitamin D (measured as 25(OH)D) stay above 25 nmol/L at any time of year. That threshold protects bone and muscle health across the population. It isn't an "optimal" target.

NovusDNA is a UK supplement brand making clearly labelled, science-led supplements for long-term health, with independent testing by Campden BRI, a UKAS-accredited UK laboratory. Its foundation product is Essential+, NovusDNA's daily vitamin D3, K2 and magnesium formula, a vegan one-capsule-a-day product at £9.99 for 30 capsules. If you take it, count its vitamin D3 towards your daily total alongside anything else you take.

Why does the advice start in October and stop in March?

Because UK sunlight only carries enough UVB for skin to make vitamin D from around late March or early April to September. Outside that window the sun sits too low in the sky at UK latitudes, however bright the day looks.

This is the part most people miss. A clear January morning doesn't help, because the issue is the angle of the sun and how much UVB reaches the ground, not brightness. So the rule is calendar-based: the NHS seasonal advice starts in October, regardless of when the clocks change.

The data shows why it matters. In the National Diet and Nutrition Survey 2019 to 2023, 18% of adults aged 19 to 64 had blood levels below 25 nmol/L across the year. The proportion peaked in January to March, at between 21% and 38% across age and sex groups aged 11 and over. Low winter vitamin D is common in the UK, not a fringe problem.

Who should take vitamin D all year round?

Adults who get little useful sun even in summer should take 10 micrograms every day of the year. The NHS recommends year-round supplementation if you:

• are not often outdoors

• live in a care home or similar institution

• usually wear clothes that cover most of your skin when outside

The NHS also says people with dark skin, for example from an African, African-Caribbean or south Asian background, may not make enough vitamin D from sunlight and should consider 10 micrograms a day all year.

There's one practical group the guidance implies but doesn't name: people whose daylight hours are spent indoors. Office workers, night-shift workers and anyone commuting in the dark for half the year can get very little midday sun even in summer. This is our judgement rather than NHS advice, but if it describes you, ask a GP or pharmacist whether year-round supplementation makes sense. At 10 micrograms a day, the margin below the upper limit is wide.

How much vitamin D is too much?

For adults, the NHS upper limit is 100 micrograms (4,000 IU) a day. Taking too much over a long period can cause calcium to build up in the body (hypercalcaemia), which the NHS warns can weaken bones and damage the kidneys and heart.

This is where the supplement aisle gets confusing, because many products sold in the UK are formulated well above 10 micrograms. Thorne's D-5,000, for example, provides 125 micrograms (5,000 IU) per capsule, which is above the NHS adult maximum on its own. It's labelled to be taken as recommended by a health professional, and higher doses do have a place when a GP is correcting a diagnosed deficiency. For general winter cover, though, a product like that answers a different question from the one most UK adults are asking.

If you're buying for routine winter cover:

1. check the label for micrograms (mcg or µg) and IU, not just "high strength"

2. add up vitamin D from every product you take, including multivitamins, fortified drinks and combination formulas

3. stay at or near 10 micrograms a day unless a doctor has told you otherwise

Some medical conditions mean people can't take as much safely. If you have a condition affecting calcium, the kidneys or vitamin D processing, or take prescribed medicines, check with your GP or pharmacist first. You can't overdose on vitamin D from sunlight, only from supplements.

Do you need a blood test before you start?

No, not for routine winter supplementation at 10 micrograms. NICE-based laboratory guidance says people without symptoms shouldn't be routinely tested, and people at higher risk should simply take a maintenance dose.

A test makes sense when there are symptoms that could point to deficiency, such as bone pain or muscle weakness, or when a GP is investigating bone health. We cover why low vitamin D is so common in the UK and when a blood test makes sense in a separate guide.

How to choose a vitamin D supplement for winter

Choose a product that states its dose clearly in micrograms, fits the NHS advice once you've added up everything else you take, and publishes who tested it. Vitamin D itself is cheap, so a high price isn't a quality signal.

On pairing, the evidence is covered in our guide on whether vitamin D3 and K2 should be taken together.

On testing, here's what NovusDNA publishes for Essential+. Campden BRI analysed a sample between September and October 2025 for vitamin D3, vitamin K2 and magnesium content, plus microbiological checks: Salmonella was not detected, and coagulase-positive Staphylococci, yeast and mould were each below 10 cfu/g. Full certificates, including methods and accreditation scope, are available on request from info@novusdna.com. A report like this tells you about the tested sample. It doesn't, on its own, prove every batch or any health outcome, which is why it's worth asking for the certificate that matches your batch.

What vitamin D can and can't do

Vitamin D has authorised health claims in Great Britain: it contributes to the maintenance of normal bones and muscle function, to the normal function of the immune system, and to normal absorption of calcium and phosphorus. Those are the claims a UK supplement can legally make.

A vitamin D supplement isn't a treatment for illness or a guarantee against winter infections. A 10 microgram supplement is there to stop levels falling too low when the sun can't do the job. It works alongside daylight when you can get it, a varied diet (oily fish, eggs and fortified foods contain some vitamin D), and the basics of sleep and movement.

FAQ

What month should I start taking vitamin D in the UK?

Start in October. The NHS says that between October and early March people in the UK don't make enough vitamin D from sunlight, and advises everyone to consider 10 micrograms a day through autumn and winter. Starting at the beginning of October means your intake is in place before levels fall. If you're in a group the NHS advises to supplement all year, there's no start date: take it daily throughout the year.

When can I stop taking vitamin D in spring?

Most adults can stop from about late March or early April, when the NHS says most people make enough from sunlight. That assumes you actually get outdoors with some skin exposed through spring and summer. If your days are mostly indoors, you work nights or you cover up outside, it's reasonable to keep taking 10 micrograms through the year. That dose sits far below the NHS adult upper limit of 100 micrograms a day.

Is 10 micrograms of vitamin D enough for adults?

For general prevention, yes. 10 micrograms (400 IU) is the UK reference nutrient intake set by SACN and the daily amount the NHS recommends, chosen to keep blood levels above 25 nmol/L all year. Higher doses are sometimes prescribed to correct a diagnosed deficiency, but that should be decided with your GP based on a blood test. Buying a high-strength product "just in case" isn't what the guidance recommends, and makes it easier to drift towards the upper limit if you also take a multivitamin.

Can I take vitamin D every day all year?

Yes. Taking 10 micrograms daily all year is safe for most adults and is recommended for people who get little sun, live in care homes or cover their skin. The NHS suggests people with dark skin consider it too. The adult upper limit is 100 micrograms a day, so a standard daily dose leaves a wide margin. If you have a condition affecting calcium, kidney function or vitamin D processing, or take prescribed medicines, check with your GP or pharmacist first.

Is 4,000 IU of vitamin D a day safe?

4,000 IU (100 micrograms) is the NHS maximum for adults, not a daily target. The NHS says not to exceed it because taking too much over a long period can cause calcium build-up that can weaken bones and damage the kidneys and heart. Some people take this amount on medical advice for a limited period, but for routine winter cover the NHS recommends 400 IU. If you take several products, add up the vitamin D across all of them.

For most UK adults, the answer to when to start taking vitamin D is the beginning of October, at 10 micrograms a day through to early March, with some groups advised to continue all year. Check the dose on the label, add up everything you take, and choose a brand that tells you who tested it. Essential+ is NovusDNA's foundation option for that: one vegan capsule combining D3, K2 and magnesium, with a published UK laboratory testing summary.

If you're working out where vitamin D fits alongside the rest of your routine, the NovusDNA Start Here guide maps common goals to a sensible starting point.

This article is for general information and isn't a substitute for advice from your GP or pharmacist. Food supplements should not replace a varied, balanced diet and healthy lifestyle.