The clocks have gone back, it's dark by half four, and most of us are heading to the gym before sunrise and leaving after sunset. Cosy? Sometimes. Great for training motivation? Not always. And there's one quiet thing that drops off for almost everyone in the UK at this time of year without us noticing: vitamin D.
This isn't a trendy new supplement or a miracle fix. It's one of the few that UK health guidance actually suggests most people think about every autumn and winter. So let's have a calm look at what it does, why it matters for people who train, and how to keep things simple.
Why winter is the problem
Your body makes most of its vitamin D from sunlight hitting your skin. In the UK, from roughly October to early March, the sun simply isn't strong enough for that to happen in any meaningful way, even on a bright, crisp day. Food helps a little (oily fish, eggs, some fortified cereals and spreads), but it's genuinely hard to get enough from diet alone.
That's why the standard UK advice is that adults consider a daily vitamin D supplement of 10 micrograms (400 IU) through autumn and winter. Some people are advised to take it all year round, including anyone who doesn't get outside much, usually covers up their skin outdoors, or has darker skin, because they make less vitamin D from sunlight.
What vitamin D actually does
Vitamin D's best-known job is helping your body use calcium and phosphate, which keeps bones, teeth and muscles healthy. It also plays a role in normal immune function, which is why it tends to come up every time winter colds start doing the rounds at work.
For anyone who trains, that bone-and-muscle side is the interesting bit. Research in athletes and active people has linked low vitamin D levels with poorer muscle function and a higher risk of stress-related bone injuries. Topping up when you're low isn't going to turn you into a different athlete overnight, but running low all winter is an easy thing to avoid.
Who should pay extra attention
- Early-morning and evening trainers. If your sessions bookend a day spent indoors, you may barely see daylight from Monday to Friday.
- Women, especially from your 40s onwards. Bone health becomes a bigger priority around and after the menopause, and vitamin D works hand in hand with calcium and strength training to support it.
- Older adults. Skin makes less vitamin D as we age, so the winter dip can be bigger.
- Runners and HYROX fans. Lots of impact and high training volume put more demand on bones, so the basics matter.
- Anyone with darker skin, or who covers up outdoors. You may need to think about vitamin D all year, not just in winter.
Keeping it simple (and sensible)
Here's the no-fuss version:
- Take it daily, with food. Vitamin D is fat-soluble, so having it with a meal that contains some fat helps your body absorb it. Breakfast or your post-gym meal both work.
- More isn't better. For most adults, 10 micrograms (400 IU) a day is the baseline advice. Plenty of supplements come in higher doses, like 25 micrograms (1000 IU), which is still well within safe limits for adults, but don't stack several products or go over 100 micrograms (4000 IU) a day unless a doctor has told you to.
- Pick a format you'll actually take. The best supplement is the one you remember. Capsules are tiny and cheap per day; gummies are handy if you hate swallowing tablets.
- Check first if you're on medication or have a health condition. A quick word with your GP or pharmacist is always worth it.
And keep doing the free stuff: get outside in daylight when you can (a lunchtime walk counts), eat oily fish a couple of times a week if that suits you, and keep lifting. Strength training is one of the best things you can do for your bones at any age.
Our picks for the darker months
If you want an easy daily option, Reflex Nutrition Vitamin D3 is a simple, no-nonsense capsule, and a tub of 100 lasts more than three months, which takes you neatly through the whole winter.
Not a fan of capsules? Nutriburst Ultra-D3 1000 IU gummies come in a lemon flavour and are an easy one to keep on the kitchen side next to the kettle.
If you're also thinking about general cover while your diet takes a winter knock, have a look at our Applied Nutrition Multi-Vitamin Complex, but check the label so you're not doubling up on vitamin D.
The bottom line
Vitamin D isn't exciting, and that's sort of the point. It's a small, cheap, well-understood habit that helps keep your bones, muscles and immune system ticking over while the UK sun takes its winter break. Take a sensible daily dose, have it with food, keep training, and let the dark mornings be the only thing you have to put up with this winter.
This article is for general information only and isn't medical advice. If you have a health condition, are pregnant, or take regular medication, speak to your GP or pharmacist before starting a new supplement.