Are you getting enough vitamin D?

If you live in the UK, the honest answer is: probably not — at least not all year round. Public Health England and the Scientific Advisory Committee on Nutrition (SACN) have been clear that most adults in the UK should consider a daily vitamin D supplement, particularly between October and March when sunlight alone cannot produce adequate amounts.

But which form of vitamin D should you take? How much do you need? And does the delivery format actually matter? Here is what the evidence says.

What does vitamin D do?

Vitamin D is a fat-soluble vitamin that the body produces in response to UVB sunlight exposure. It also comes from a small number of dietary sources including oily fish, egg yolks, and fortified foods.

Under EU Regulation 432/2012 (retained in UK law), the following health claims are authorised for vitamin D:

These are the only health claims that can be legally made about vitamin D in the UK. Any supplement brand claiming it "boosts immunity" or "prevents bone disease" is operating outside regulatory boundaries.

How common is vitamin D deficiency in the UK?

Vitamin D deficiency is well-documented as a public health concern in the UK. The National Diet and Nutrition Survey (NDNS) has consistently shown that a significant proportion of the UK population has low vitamin D status, particularly during winter and spring.

A large-scale standardised analysis across European populations found that approximately 13% of over 55,000 individuals had serum 25(OH)D concentrations below 30 nmol/L — the threshold widely used to define deficiency — rising to 17.7% during extended winter (Cashman et al., 2016).

In 2016, SACN published its landmark Vitamin D and Health report, which recommended that:

NICE guidance (PH56) reinforces these recommendations and identifies specific population groups who should supplement throughout the year.

D3 vs D2 — which form is better?

This is one of the most important and frequently overlooked distinctions in vitamin D supplementation. There are two supplemental forms:

What does the research show?

A systematic review and meta-analysis by Tripkovic et al. (2012) — published in the American Journal of Clinical Nutrition — compared the efficacy of vitamin D2 and D3 in raising serum 25-hydroxyvitamin D [25(OH)D] status. The analysis concluded that vitamin D3 is significantly more effective than vitamin D2 at raising and maintaining overall 25(OH)D concentrations.

This was further supported by Heaney et al. (2011), published in the Journal of Clinical Endocrinology & Metabolism, which demonstrated that vitamin D3 is approximately 87% more potent than vitamin D2 in raising serum 25(OH)D, and produces two to three times greater storage of vitamin D.

The same research group followed up with a randomised, placebo-controlled food-fortification trial (Tripkovic et al., 2017) confirming that daily supplementation with 15µg of vitamin D3 was more effective than the same dose of D2 at increasing wintertime 25(OH)D status in both South Asian and white European women in the UK.

The bottom line on D3 vs D2

If you are choosing a vitamin D supplement, the evidence consistently favours D3 (cholecalciferol). This is also the form recommended as first choice by NICE for treating vitamin D deficiency. D2 is not ineffective, but it requires higher doses to achieve the same serum levels as D3.

PARTICULAR uses vitamin D3 (cholecalciferol) — the more bioavailable form — in its formulations.

How much vitamin D should you take?

The SACN 2016 report established the UK Reference Nutrient Intake (RNI) for vitamin D at 10 micrograms (400 IU) per day for the general population aged one year and above. This recommendation is designed to maintain serum 25(OH)D concentrations above 25 nmol/L in the majority of the population throughout the year.

Key points on dosing:

Many high-street supplements provide 25µg (1,000 IU) or even 100µg (4,000 IU) per day as a standard dose. While these are within the safe upper limit, they may not be necessary for everyone. A personalised approach is more appropriate.

What about vitamin D cofactors — K2 and magnesium?

Vitamin D does not work in isolation. Two nutrients play particularly important roles alongside it:

Vitamin K2 (MK-7)

Vitamin D contributes to normal absorption of calcium, but calcium needs to be directed to the right places — bones and teeth — rather than accumulating in soft tissues. Vitamin K2 (as MK-7) contributes to the maintenance of normal bones and supports normal blood clotting. Taking vitamin D alongside K2 is a well-established complementary approach in evidence-based supplementation.

Magnesium

Magnesium is a cofactor in the enzymatic conversion of vitamin D to its active form in the body. Without adequate magnesium, vitamin D metabolism may be impaired. Magnesium itself contributes to normal muscle function, normal functioning of the nervous system, and the reduction of tiredness and fatigue — making it a natural companion to vitamin D for overall wellbeing.

If you are supplementing vitamin D, it is worth ensuring your magnesium and K2 intake is also adequate.

How PARTICULAR delivers vitamin D

Most vitamin D supplements on the UK market come as tablets, capsules, or sprays — all delivering a fixed, one-size-fits-all dose. PARTICULAR takes a different approach.

Microgranule format

Each vitamin D3 granule is individually coated, allowing it to be released and absorbed independently in the gut — separate from other nutrients that might compete for absorption. You can read more about how this works on our science page.

Personalised dosing

Your vitamin D3 dose is calibrated based on your questionnaire responses, accounting for factors including your typical sun exposure, skin type, dietary intake, and time spent outdoors. Rather than guessing at a flat dose, PARTICULAR adjusts to complement what your body is likely already getting.

Synergistic formulation

Because vitamin D, K2 (MK-7), calcium, and magnesium all interact, PARTICULAR delivers them together in one daily scoop — but as separate microgranules, so each nutrient is absorbed optimally without interfering with the others.

Key takeaways

  1. Vitamin D contributes to normal immune system function, maintenance of normal bones, normal muscle function, and normal absorption of calcium — these are EU-authorised health claims
  2. A significant proportion of the UK population has insufficient vitamin D levels, particularly during autumn and winter — SACN recommends 10µg (400 IU) daily for all adults
  3. Vitamin D3 is more effective than D2 at raising serum 25(OH)D levels — supported by systematic reviews and randomised controlled trials (Tripkovic et al., 2012; Heaney et al., 2011)
  4. Cofactors matter — vitamin K2 (MK-7) and magnesium both play important roles alongside vitamin D
  5. A personalised dose based on your lifestyle and diet is more appropriate than a flat one-size-fits-all amount
  6. Microgranule delivery ensures vitamin D3 is absorbed independently from competing nutrients, with targeted intestinal release

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