Vitamin D for runners through autumn and winter

Autumn is the point in the year when running gets harder to fuel in ways that are easy to miss. The mornings are darker, the sun sits lower, and one quiet change happens under the surface: your body more or less stops making vitamin D. For anyone logging miles through a British winter, that is worth understanding, because vitamin D plays a real role in how your bones, muscles and immune system cope with training.

Why do UK runners run low on vitamin D in winter?

Most of our vitamin D does not come from food. It comes from sunlight, specifically UVB rays hitting bare skin. The problem is latitude. Across the UK, from about October to early March the sun sits too low in the sky for that UVB to do its job, so the skin cannot make meaningful amounts of vitamin D no matter how long you are outside. A frosty lunchtime run in January feels healthy, and it is, but it will not top up your vitamin D the way a July afternoon would.

Runners face a few extra factors on top of the seasonal one. Winter training often happens before or after work, in the dark. When you do run in daylight you are usually covered head to toe in leggings, a jacket, gloves and a hat, so very little skin is exposed. Add cloud cover and short days, and it is easy to go months with almost no sun on your skin.

What does vitamin D actually do?

Vitamin D helps your body regulate calcium and phosphate, the minerals that keep bones, teeth and muscles healthy. For runners, the bone angle matters. Repetitive loading is part of the sport, and healthy bones are part of staying resilient to stress injuries over a long training block. Vitamin D also supports normal muscle function, and it plays a part in a healthy immune system, which is why it gets so much attention during cold and flu season.

It is worth being honest about the limits here. Vitamin D is not a magic shield, and it will not stop you catching every winter bug. What the guidance supports is keeping your levels in a healthy range so these normal processes can work as they should.

What does the NHS recommend?

The official UK advice is straightforward. Adults and children over the age of one need around 10 micrograms (400 IU) of vitamin D a day. Because we cannot rely on sunlight in the darker months, the NHS advises that everyone should consider taking a daily supplement containing 10 micrograms of vitamin D during the autumn and winter, roughly October to early March.

Some groups are advised to supplement all year round rather than just in winter, which we cover below. And there is an upper limit worth respecting: adults should not take more than 100 micrograms (4,000 IU) a day, as consistently high doses can be harmful.

Can you get enough from food?

Food helps, but it rarely does the whole job, which is exactly why the supplement advice exists. The richest natural sources are oily fish. Egg yolks, red meat and liver contain smaller amounts, and many everyday products are fortified with vitamin D. If you eat oily fish a couple of times a week you are giving yourself a genuine head start. For most people, though, hitting 10 micrograms a day from food alone through winter is hard, especially if your diet is plant based or you do not eat much fish. A cheap daily supplement is the simple fix the guidance points to.

• Oily fish such as salmon, sardines, trout, herring and mackerel
• Egg yolks
• Red meat and liver
• Fortified foods such as some breakfast cereals and fat spreads

If you follow a vegan or vegetarian diet it is worth knowing that most natural food sources are animal based, and many supplements use vitamin D3 from animal sources. Vegan-friendly options do exist, including supplements made from lichen, and some fortified plant milks and cereals carry vitamin D, so it is worth checking the label.

Who is at higher risk of running low?

Everyone in the UK is more likely to be low in winter, but some people are at higher risk and are advised to consider a supplement throughout the year, not only in the colder months.

• People who spend little time outdoors, or who are largely housebound
• People who cover most of their skin when outside
• People with darker skin, for example those with an African, African-Caribbean or south Asian background, because more melanin reduces how much vitamin D the skin makes from sunlight
• People living in care settings

Runners are not automatically higher risk, but if you train almost entirely indoors on a treadmill, or you fit your outdoor sessions into the dark edges of the day, your sun exposure may be as low as anyone's.

Does more vitamin D make you a faster runner?

This is where it pays to be careful, because the honest answer is nuanced. If you are genuinely deficient, correcting that shortfall can help. Studies in people who started low have linked improving vitamin D status to better muscle strength and measures of performance. That makes sense, because you are fixing something that was holding the body back.

What the evidence does not show is a bonus for topping up beyond a healthy level. Once your vitamin D is in a sufficient range, taking more does not appear to add extra strength, power or endurance. In other words, correcting a deficiency matters, but megadosing does not turn a healthy runner into a faster one, and very high doses over time can be harmful rather than helpful.

The sensible takeaway is not to chase big numbers. Aim to avoid a winter dip, keep to the recommended amount, and treat vitamin D as one small, useful habit rather than a performance hack. If your training feels flat this winter, the more likely culprits are sleep, fuelling, easy-day discipline and consistency, not a single vitamin.

How can you keep your levels up sensibly?

A few simple habits cover most people.

• Take a daily 10 microgram (400 IU) supplement from roughly October to early March. If you are in a higher-risk group, consider it year round.
• Get outside in daylight when you can. It will not make much vitamin D in deep winter, but daylight is good for sleep and mood, both of which help your training.
• Include oily fish and fortified foods in your week where they fit your diet.
• Do not exceed 100 micrograms (4,000 IU) a day, and do not start high-dose supplements on a whim.
• If you have had stress injuries, feel persistently run down, or want to know your actual level, speak to a GP or pharmacist. A blood test can tell you where you stand, and they can advise on the right dose for you.

Consistency beats intensity here. A small daily habit through the darker months does far more than an occasional large dose.

Nutrition is only one piece of training well through winter. The bigger wins usually come from a plan that balances your running, strength and recovery so you stay healthy enough to keep showing up. That is the thinking behind Edge, where 18,000+ members train across running, strength, HIIT and mobility in one joined-up plan.

This article is general guidance, not medical advice. If you are new to exercise, returning from injury, pregnant, or managing a health condition, speak to your GP before starting, and see a physio for any niggle that does not settle.