Vitamin D in Winter: What the UK Guidance Says
The UK guidance is simple: during autumn and winter, everyone should consider taking a daily supplement of 10 micrograms (400 IU) of vitamin D. The NHS says that between October and early March the sunlight in the UK is not strong enough for our skin to make it. Some people are advised to take 10 micrograms all year round, and adults should not take more than 100 micrograms (4,000 IU) a day unless a doctor has advised it. That is most of what you need to know. The rest of this post explains who the year-round advice covers, where food fits in, and how it relates to people who train.
I am a personal trainer, not a doctor or dietitian, so everything below comes from published NHS guidance. If you have a medical condition or take regular medication, ask your GP or pharmacist before starting any supplement.
Why winter matters in London
Most of our vitamin D is made in the skin when it is exposed to sunlight, specifically the UVB part of it. At London’s latitude, the sun in winter sits too low in the sky for enough UVB to get through. The NHS says that from about late March or early April to the end of September, most people can make all the vitamin D they need from sunlight on their skin. Outside that window, they cannot, however much time they spend outdoors.
That is worth stressing because it surprises people. A brisk lunchtime walk across Highgate Wood in January is good for plenty of things, but it will not top up your vitamin D. Neither will sitting by a sunny window, since glass blocks UVB.
What the NHS recommends, in one table
The figures below are from the NHS page on vitamin D, which is worth reading in full.
| Who | Advice |
|---|---|
| Adults and children over 1, including pregnant and breastfeeding women | Consider 10 micrograms a day in autumn and winter |
| People rarely outdoors, such as the frail or housebound, or living in a care home | 10 micrograms a day all year |
| People who usually cover most of their skin outdoors | 10 micrograms a day all year |
| People with dark skin, for example of African, African-Caribbean or South Asian background | Consider 10 micrograms a day all year |
| Children aged 1 to 4 | 10 micrograms a day all year |
| Babies under 1 | Specific advice depending on feeding; see the NHS page |
Micrograms and IU
Labels use both. 10 micrograms is the same as 400 IU (international units). 25 micrograms is 1,000 IU. If a bottle in a health shop says 4,000 IU, that is 100 micrograms, which is the NHS upper limit for adults, not a daily target.
More is not better
The NHS advises adults, including older people and pregnant or breastfeeding women, not to take more than 100 micrograms a day, as it could be harmful. Taking too much over a long period can cause calcium to build up in the body, which can weaken bones and damage the kidneys and heart. Children have lower limits.
In practice, a lot of people end up over-supplementing by accident: a standalone vitamin D tablet, plus a multivitamin, plus a fortified drink or cereal. Add up what is in everything you take before buying something stronger. If your GP has prescribed a higher dose after a blood test, follow that, since it is tailored to you.
Can you get enough from food?
Not easily. Vitamin D is found in a small number of foods:
- Oily fish such as salmon, sardines, herring, trout and mackerel.
- Egg yolks.
- Red meat and liver (the NHS advises avoiding liver in pregnancy).
- Fortified foods, including some fat spreads and breakfast cereals.
Cows’ milk in the UK is generally not fortified, so it is not a reliable source. Even with a good diet, it is hard to reach 10 micrograms every day from food alone, which is why the government guidance focuses on supplements in winter. Food still matters, though, and oily fish once or twice a week is sensible for plenty of other reasons.
A practical winter checklist
- Start a 10 microgram daily supplement in October, unless you already take one or your doctor has advised otherwise.
- Check the labels of anything else you take and add up the total.
- Keep it at 10 micrograms unless a doctor recommends more. You do not need to “load”.
- Take it with a meal; it is a fat-soluble vitamin and that is an easy habit to anchor.
- Carry on until early March, then let spring and summer sunlight take over, taking care not to burn.
- If the year-round categories in the table apply to you, keep going through summer too.
- If you have symptoms that worry you, such as persistent bone or muscle pain, see your GP rather than self-treating with large doses.
Where this fits for people who train
Vitamin D is needed for the body to absorb calcium and phosphate, which keep bones, teeth and muscles healthy. That is the well-established role, and it is enough reason for anyone doing regular strength training to take the guidance seriously. Strength training itself is one of the best things you can do for your bones as you get older; vitamin D is part of the background that supports it.
What you will read online about vitamin D boosting performance, strength or testosterone in people who already have enough is a different matter, and the evidence is not strong enough for me to repeat it. Treat the supplement as covering a seasonal shortfall, not as a training aid.
Winter is also when routines slip. Darker mornings, colder commutes and the run of December dinners make it easy to train less and sleep worse. A fixed appointment helps more than any supplement, which is one reason clients book private 1-1 sessions in Highgate for early mornings and evenings through the winter months. Our posts on winter workout motivation and strength training for bone density cover the other half of the picture.
What we will and will not advise at the studio
As a trainer, I can point you to the NHS guidance and help you build habits around food, sleep and movement. I do not diagnose deficiencies, recommend high-dose products, or interpret blood tests; that belongs with your GP or a registered dietitian. If you want help with the training side, our personal trainer page explains how sessions work at The Highgate House, a few minutes’ walk from Highgate tube.
Questions we get asked
Should I get a blood test before taking vitamin D?
The NHS guidance on 10 micrograms in winter does not require a test. If you have symptoms or a condition that affects absorption, speak to your GP, who can decide whether a test is needed.
Does a holiday in the sun count?
A week of strong sun may raise levels temporarily, but it does not replace the winter guidance. Keep taking the supplement when you return.
Is a daylight lamp the same thing?
No. Light boxes sold for winter mood do not generally emit UVB and do not produce vitamin D in the skin.
Can I take it with my other supplements?
Usually, but check the total vitamin D across everything, and ask a pharmacist if you take prescribed medication.
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