Come spring, the collective assumption tends to be: right, the sun’s back, the supplements can go back in the drawer, we’re fine now. We are, regrettably, not necessarily fine. The gap between “the sun is out” and “your body is actually synthesising enough vitamin D” is wider than most people realise, and the misconception that warmer months automatically solve the problem means a lot of us are running low for far longer than we think.

Around one in six adults in England is low in vitamin D right now according to the NHS. Not “could do with a little more” deficient but actually, measurably low. Given that we’re talking about a vitamin that’s essential for your bones, your muscles, and your immune system, that’s a fairly significant thing to be running short on.

So, in this feature, we’re diving into all things vitamin D – what it actually does in the body, what to eat, and whether you should be taking a supplement (and if so, which one). Stay with us.

So what does vitamin D actually do?

Vitamin D is technically a fat-soluble vitamin, but once it’s active in the body it behaves more like a hormone. Its primary job is helping your intestines absorb calcium and phosphate from food – which sounds deeply unglamorous, but the downstream effects are anything but minor.

Without enough of it, your body can’t absorb calcium properly, regardless of how much dairy you’re eating or how conscientiously you’re adding seeds to your morning yoghurt. The results show up in your bones first – insufficient vitamin D over time leads to weakened, softer bones (osteomalacia in adults; rickets in children, which has been inconspicuously making a comeback in the UK in recent years).

Beyond that, vitamin D receptors are present in muscle tissue, so adequate levels are linked to better muscle strength and function. And it plays a genuine role in immune regulation – not in the “boost your immunity” way that supplement brands love to promise, but in a more fundamental, behind-the-scenes modulation of how your immune system responds. In short: it has specific, essential jobs, and a lot of us aren’t giving our bodies enough of it to do them.

Vitamin D vs D2 vs D3: What are the differences?

It’s likely you’ll see D3 a lot in supplements, so it’s worth knowing what that 3 is all about. Vitamin D is the overall term, but it comes in two main forms: D2 and D3. Both are used by the body in the same way once processed, but the difference lies in where they come from and how effectively they work.

Vitamin D2 (ergocalciferol) is typically found in plant sources and some fortified foods, while vitamin D3 (cholecalciferol) is found in animal-based foods and is the form your body naturally produces when exposed to sunlight. The key distinction is that D3 is generally more potent and stays in the body for longer, making it more effective at maintaining healthy vitamin D levels.

Why is vitamin D deficiency so common here?

According to the National Institutes of Health, most of our vitamin D isn’t supposed to come from food – it’s produced in the skin when it’s exposed to UVB radiation from sunlight. Which works brilliantly if you live somewhere with reliable sun. The UK, famously, does not.

From October through to March, UVB levels in the UK are too low for the skin to synthesise vitamin D in any meaningful quantity. The sun is at the wrong angle. It doesn’t matter how long you stand in it – six months of the year, this particular route is closed. And the other six months? Less straightforward than people tend to assume. Most of us spend the vast majority of our days indoors and when we are outside, we’re in layers, often wearing SPF (important), and more often than not under cloud cover that cuts UVB intensity further.

The conditions that actually support skin synthesis (exposed skin, direct midday sun, clear skies) don’t describe a typical British Tuesday in any season.

Can’t you just eat your way out of it?

You can certainly try. According to dietitians, oily fish are the standout dietary sources: salmon, mackerel, sardines, herring. Egg yolks contribute smaller amounts. Some breakfast cereals, certain spreads, and a range of plant-based milks are fortified with it. Eating these foods regularly is useful and genuinely worth building into your diet.

But useful isn’t the same as sufficient. The natural sources are limited, and the quantities you’d need to eat consistently to maintain adequate levels through food alone are unrealistic for most people.

So while technically yes, you can eat your way out of your vit D deficiency, you would need to be regularly eating oily fish multiple times per week, and even then it depends on portion size and type of fish. Most people in the UK have average dietary intakes that fall below recommended levels before sunlight even enters the equation.

Who needs to pay the most attention?

Everyone in the UK is dealing with the same seasonal shortfall. But some groups are carrying additional disadvantages on top of that.

People with darker skin tones produce vitamin D less efficiently from sunlight, because higher melanin levels reduce UVB absorption. The same sun exposure produces less vitamin D, which means the already-narrow British summer window is narrower still. UK primary care studies show substantially higher deficiency rates among South Asian and Black populations, with some research suggesting deficiency is far more common in certain ethnic minority groups than the general average already implies.

Older adults produce vitamin D less efficiently through the skin as they age, regardless of how much time they spend outside. They’re also more likely to spend significant time indoors, and the consequences of deficiency for this group are particularly serious – reduced bone density, increased fall risk, greater likelihood of fractures.

People who cover most of their skin for cultural, religious, or personal reasons, or those with long commutes, desk jobs, and indoor-heavy lifestyles (which is most of us) also suffer. For all of these groups, “get a bit more sun” is an incomplete answer at best.

How much Vitamin D do you actually need?

NHS advice is unusually clear on this: 10 micrograms (400 IU) of vitamin D per day is recommended for most adults and children over the age of one.

10 micrograms is a baseline to maintain healthy levels in most people who aren’t significantly deficient. If you’re in a higher-risk group, or you have symptoms that might suggest your levels are genuinely low (persistent fatigue, bone pain, getting ill more than feels normal), your GP can test your levels with a simple blood test and advise a higher dose if needed.

Megadosing without knowing your baseline isn’t advised – but for most people, the 10-microgram daily recommendation is where to start. Vitamin D supplements are affordable and widely available in pharmacies and supermarkets.

Which supplement should you actually get?

For most people, a standard vitamin D3 supplement at 10 micrograms (400 IU) is exactly what’s needed. D3 is the form your body produces naturally and tends to be more effective at raising and maintaining blood levels than D2.

If you’re vegan or vegetarian, the majority of D3 supplements are derived from lanolin (sheep’s wool), so you’ll want to look for a lichen-based D3 or a D2 supplement specifically labelled vegan. D3 is generally considered more effective – but a good quality vegan D3 from lichen covers you on both counts.

Beyond that, the usual rules for supplements apply. Look for brands that are transparent about their sourcing, that undergo third-party testing, and that don’t pad the formula with unnecessary fillers. Vitamin D is fat-soluble, so taking it with a meal that contains some fat helps with absorption – something to keep in mind if you tend to take supplements on an empty stomach in the morning.

Options are endless, but two vitamin D supplements we tried and can recommend include Nutravita’s 4000IU vitamin D3, which costs £17.99 and will last you for over an year, and Puresport’s 4000IU vitamin D3, which is available for £25 and contains 60 capsules.

Price-wise, there’s a clear winner, but it’s important to note that Puresport’s is totally vegan, while Nutravita’s capsules contain gelatine. Puresport’s also contain 100mcg of K2, which helps guide where that calcium goes. Barring that, both are excellent options that deliver strong levels of vitamin D (higher than the recommended intake, but still safe for daily use).

Get your vitamin D fix

Vitamin D deficiency is quiet, but the effects accumulate over months: bones and muscles deteriorating slowly, immune function dipping in ways that are easy to attribute to other things. People notice when they’re iron deficient or dehydrated. Vitamin D doesn’t tend to announce itself in the same way. Whichever supplement you choose, make sure to follow your GP’s directions and get your blood tested so you can get the exact dosage you need.

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