Vitamin D is one of the most talked-about nutrients in the UK — and for good reason. Government data consistently shows that a significant proportion of British adults have vitamin D levels below the recommended threshold, particularly from October through to March.
But why is this so widespread in the UK specifically? What does vitamin D actually do in the body? And what should you look for if you're choosing a supplement?
This guide breaks it all down — no hype, just the facts.
Why Vitamin D Deficiency Is So Common in the UK
Your body produces vitamin D when UVB radiation from sunlight hits your skin. The problem? The UK sits between latitudes 50°N and 60°N. From roughly October to March, the sun simply doesn't rise high enough for your body to produce meaningful amounts — regardless of how much time you spend outdoors.
That's nearly half the year where sunlight alone can't do the job. And it gets worse if other factors apply to you.
You're at higher risk if you: spend most of the day indoors, have darker skin (which requires more UVB exposure to synthesise the same amount), cover most of your body when outside, are over 65 (the skin becomes less efficient with age), or follow a diet low in oily fish, eggs, and fortified foods.
What Does Vitamin D Actually Do in the Body?
Vitamin D isn't just "the sunshine vitamin" — it plays a role in multiple systems throughout the body. The following are not marketing claims. They're EFSA-approved health claims, authorised under EU and UK nutrition regulations:
🔬 EFSA-Approved Vitamin D Health Claims
- Contributes to the normal function of the immune system
- Supports the maintenance of normal bones and teeth
- Plays a role in the process of cell division
- Contributes to normal absorption and utilisation of calcium and phosphorus
- Contributes to the maintenance of normal muscle function
- Needed for normal growth and development of bone in children
In short: vitamin D is involved in your bones, your muscles, your immune function, and how your body uses key minerals. When levels drop, multiple systems are affected.
What the NHS Recommends
The UK government's advice is clear: everyone should consider taking a daily vitamin D supplement during autumn and winter. For people who spend most of their time indoors, cover their skin when outside, or have darker skin, supplementation is recommended year-round.
The baseline recommendation is 10 micrograms (400 IU) per day. However, many people — particularly those with confirmed low levels via blood testing — opt for higher-strength supplements under the guidance of their healthcare provider.
"The UK government recommends everyone considers a daily vitamin D supplement during autumn and winter."
Why Vitamin D3 and K2 Are Taken Together
This is one of the most important things to understand about vitamin D supplementation — and something many people miss.
Vitamin D3 helps your body absorb calcium. But calcium on its own doesn't automatically go to the right places. Without proper direction, it can accumulate in soft tissues rather than in bones and teeth where it's needed most.
That's where vitamin K2 comes in. Vitamin K2 — specifically the MK-7 form — activates proteins that help direct calcium to bones and teeth. Think of D3 as the key that lets calcium in, and K2 as the guide that tells it where to go.
D3 vs D2 — Which Form Is Better?
There are two forms of supplemental vitamin D: D2 (ergocalciferol) and D3 (cholecalciferol). D3 is the form your body naturally produces from sunlight, and research suggests it's more effective at raising and maintaining blood levels of vitamin D.
| Factor | Vitamin D2 | Vitamin D3 |
|---|---|---|
| Source | Plant/fungal | Sunlight / animal / lichen |
| Potency | Lower | Higher — more effective at raising blood levels |
| Half-life | Shorter | Longer — stays active in the body longer |
| NHS/EFSA preferred | Accepted | Generally preferred in research |
The Role of Magnesium (Often Overlooked)
Here's something most people don't realise: vitamin D can't be properly utilised by the body without adequate magnesium.
Magnesium is required to convert vitamin D into its active form in the body. Without enough magnesium, vitamin D remains stored and inactive — meaning you could be supplementing with D3 and still not getting the full benefit.
Research published in The Journal of the American Osteopathic Association found that vitamin D metabolism depends on magnesium, and that magnesium deficiency can reduce the effectiveness of vitamin D supplementation.
The magnesium connection: Magnesium activates the enzymes that convert vitamin D into its usable form. It also plays a role in calcium transport — working alongside K2 to support where calcium ends up in the body. If you're supplementing with D3, making sure your magnesium intake is adequate is a smart move.
This is one of the reasons why well-formulated vitamin D supplements now include magnesium alongside D3 and K2 — to support the full metabolic chain rather than just one part of it.
What to Look For in a Vitamin D Supplement
Not all vitamin D supplements are equal. Here's what matters when choosing one:
The body's natural form. More effective than D2 at raising blood levels. Look for meaningful doses — 1,000 to 10,000 IU depending on your needs and your healthcare provider's guidance.
Directs calcium to bones and teeth. MK-7 has a longer half-life than MK-4, meaning it stays active in the body longer. A key companion to D3.
Supports heart, brain, and joint wellness. Also enhances the absorption of fat-soluble vitamins like D3 — making the formula work harder for you.
One of nature's most potent antioxidants, sourced from microalgae. Supports the body's defence against oxidative stress and complements the D3+K2 formula.
Required to convert vitamin D into its active form. Glycinate is one of the most bioavailable and gentle forms of magnesium — well absorbed without digestive discomfort.
Vitamin D is fat-soluble — it needs fat to be absorbed properly. Organic coconut oil acts as the delivery system, ensuring maximum uptake from every softgel.
Quick Checklist: Choosing a Quality Vitamin D Supplement
- D3 not D2 — cholecalciferol is the preferred form
- K2 as MK-7 — supports calcium metabolism alongside D3
- Oil-based softgels — fat-soluble vitamins need fat for absorption
- Magnesium included — required to activate vitamin D in the body
- Third-party tested — independent verification of what's actually in the bottle
- No unnecessary fillers — clean formulations with ingredients that serve a purpose
Vitamin D3 10,000 IU + K2 500mcg MK-7
- 10,000 IU Vitamin D3 (Cholecalciferol)
- 500mcg Vitamin K2 (MK-7)
- Omega-3 (DHA + EPA) — 100mg
- Astaxanthin — 1mg
- Magnesium Glycinate — 25mg
- Organic Coconut Oil base
- 180 vegan softgels — 6-month supply
- Independently tested by Eurofins