The sunshine vitamin: Your definitive guide to vitamin D

By: Jo Woodhurst

9 Min read

In this article:

What is vitamin D and why do we need it?
From sunlight to every cell: How the body makes vitamin D
Are you getting enough?
Which regions are at risk of low vitamin D levels?
Know your vitamin D levels: How to check
Supplementing with vitamin D: What to consider
True D3 and K2: Nutrients working in synergy
How to take vitamin D: Optimising your absorption
Beyond supplementation: More ways to support your vitamin D

For most of human history, vitamin D arrived through rhythm. Sunlight on skin. Time outdoors. Modern life has disrupted that rhythm, with many of us spending most of our day indoors, receiving little meaningful exposure to the UV light needed for vitamin D synthesis.

Yet, while our lifestyles might have shifted, vitamin D remains essential to human health. This raises the question: “How can we be sure we’re getting enough?”

From how vitamin D works in the body to the simple test you can do to check your levels, Jo Woodhurst walks you through everything you need to know about the sunshine vitamin.

What is vitamin D and why do we need it?

Vitamin D is the term used to describe a group of fat-soluble compounds. This group includes Vitamin D2, which is mainly found in plants and fungi, as well as Vitamin D3 - the form our skin produces when exposed to UVB sunlight and that’s commonly used in food supplements.

The body mainly uses vitamin D for:

+ Immune resilience: Supporting the normal function of the immune system
+ Bone health: Maintaining strong bones and teeth
+ Mobility and recovery: Maintaining normal muscle function
+ Calcium: To absorb and stabilise blood calcium levels
+ Brain health: For cell division, and emerging research explores a role in mood support.

Almost every tissue in your body has a Vitamin D receptor, from brain to bone to immune cells, which shows how essential this vitamin is.

From sunlight to every cell: How the body makes vitamin D

Vitamin D has a fascinating journey through the body, beginning with something as simple as sunlight.

When the sun’s UVB rays reach your skin, they trigger a natural process that transforms a compound already present in your skin into vitamin D3. At this stage, vitamin D isn't ready to be used by the body; it needs a little help from two organs.

First, it travels to the liver, where it's converted into a form called 25-hydroxyvitamin D. From there, it moves to the kidneys, which transform it into its active form, known as calcitriol.

Only then can vitamin D get to work, helping to regulate a range of important processes throughout the body.

This journey, from sunlight to skin, liver to kidneys, is part of what makes vitamin D so interesting. Unlike many other vitamins, it behaves more like a hormone, being made, activated and carefully regulated by the body before sending signals to where they're needed. A small reminder of just how interconnected our bodies really are.

Suboptimal vitamin D: Are you getting enough?

Despite its importance, as many as 50% of UK adults have low vitamin D levels (1).

Our skin needs UVB radiation to make vitamin D. And in the UK, getting enough of it isn't always straightforward.

Even when the sun is shining, modern life can leave us with a sunlight gap. We spend more time indoors, often behind screens, and sunscreen can limit the UVB exposure needed for vitamin D production.

Add to this the UK's long winters, when the sun sits too low in the sky for our skin to make meaningful amounts of vitamin D, and maintaining healthy levels throughout the year isn't always straightforward.

So, while regular walks, gardening and time in nature are all brilliant for our wellbeing and can contribute to vitamin D production, they may not always be enough to meet your needs.

How much vitamin D your skin makes depends on the season, time of day, skin tone, how much skin is exposed and whether you're wearing sunscreen. While 10-15 minutes of midday sun may be enough for some people in summer, this varies considerably.

The vitamin D we make during sunnier months can help carry us through winter, but those reserves may not be enough for everyone.

Which regions are at risk of low vitamin D levels?

All regions in the UK are advised to consider vitamin D supplementation in the winter months, but even those who live in sunny places like Spain can have low vitamin D.

That’s because vitamin D production depends on several factors, including latitude, age, SPF use, skin tone, season and the duration of time spent outdoors.

Other nutrients play a role too. The body also needs enough magnesium (to help convert it to a form it can use) and vitamin K2 to help direct the calcium that vitamin D helps to absorb to bones. Complex? Yes, and a reminder that nutrients do not work alone.

And it's not just where you live that matters. Some groups are more vulnerable to vitamin D deficiency or insufficiency. This includes:

Those who are pregnant or breastfeeding – to support baby’s development (3)
Babies and children – to help aid growth and brain development (4)
Those with darker skin may need to spend longer in the sun to produce adequate amounts of vitamin D (5)
Vegans/vegetarians may also want to take into account that many foods rich in vitamin D are mainly animal-derived

Know your vitamin D levels: How to check

It's for this reason that in the UK, the NHS advises everyone over the age of 4 to take 10 µg (400 IU) daily in autumn and winter (October to March) (2).

This is a general recommendation to help maintain vitamin D levels across the population, but individual needs can vary depending on factors we’ve explored above. For some people, a higher daily intake may be appropriate, particularly if their vitamin D levels are already low.

A simple blood test to actually know where your levels stand can be a useful tool, especially given how insufficiency is often easy to miss.

If you’re unsure whether you’re getting enough vitamin D, you can get your vitamin D levels checked, either through your GP or with a simple finger-prick test that you can order online.

Testing towards the end of winter or early spring can provide a useful indication of whether your levels have remained adequate through the darker months. Testing later in the summer can also offer insight into how your levels respond to increased sunlight exposure.

If your levels remain low despite adequate sun exposure and dietary intake, it's worth speaking to your GP about possible contributing factors.

Supplementing with vitamin D: What to consider

In addition to knowing your vitamin D levels, there are a few other things to consider when deciding whether supplementing your vitamin D is right for you.

Time spent outdoors: Do you spend most of your time outside, or does indoor living reduce your sun exposure across most of the year?

Absorption: Do you have any conditions that may interfere with your body's ability to absorb and use vitamin D supplements? This makes the format of your vitamin D supplement an important consideration. Oral sprays tend to be the most well-absorbed form and may be the best choice for people with fat malabsorption issues or low dietary fat intake.

Vitamin D is fat-soluble, which means dietary fat helps the body absorb it. Taking vitamin D alongside a meal containing fat can therefore be a useful consideration when choosing how to supplement. Our True D3 + K2 spray uses an MCT oil base, providing a fat-containing format for these fat-soluble nutrients.

Duration: While vitamin D is generally considered a safe supplement, if you are taking a high dose (over 10ug) for a prolonged period (over 5 months), it is best to consult your GP.

Taking excessive amounts of vitamin D over time can lead to a build-up of calcium in the blood, which may cause symptoms such as nausea and, in serious cases, kidney problems (6). This is why it's important to follow recommended dosages and seek professional advice if you're considering a higher intake.

If you are taking multivitamin supplements, it is also worth checking whether it already contains vitamin D so that you know exactly how much you are taking.

True D3 and K2: Nutrients working in synergy

When formulating True D3 + K2, we wanted to create a convenient daily ritual to support vitamin D intake throughout the year, particularly during the darker months.

That’s why we started with bioavailability at the core, using a considered daily dose of Vitamin D₃ 50 µg (2000 IU), layered with Vitamin K₂ – 50 µg (MK-7) and suspended in an MCT oil lipid carrier. These carefully considered amounts sit comfortably within established safety limits while providing meaningful nutritional support.

Every ingredient earned its place.

+ Vitamin D₃ at an evidence-based daily dose shown to be effective in clinical trials

+ A meaningful amount of K2 to support normal calcium metabolism.

+ MCT oil: For optimal absorption

+ Rosemary oil: contributes subtle herbal notes whilst also helping to protect fat-soluble vitamin D

+ Peppermint: Adds a fresh flavour experience, making it a ritual that's easy to return to every morning.

Vitamin D and Vitamin K2 are often discussed together because they are both involved in calcium metabolism, supporting different stages within the same physiological process.

Vitamin D helps the body absorb calcium from the digestive tract and contributes to maintaining normal blood calcium concentrations.

Vitamin K2 supports what happens next. As the MK-7 form of vitamin K, it contributes to the maintenance of normal bones by activating vitamin K-dependent proteins involved in bone mineralisation.

Both vitamins D and K are fat-soluble nutrients, meaning they are naturally absorbed alongside dietary fats. For this reason, True D3 + K2 delivers them within an MCT oil base, providing a stable lipid environment that helps keep fat-soluble nutrients evenly dispersed.

We chose the spray format, not only because it’s a convenient format to support consistent daily use, but also because it provides an alternative to tablets for consumers who prefer non-pill formats.

This is Vitamin D delivered as it should be: with fat, with cofactors, crafted with the utmost respect for physiology.

How to take vitamin D: Optimising your absorption

Our vitamin D spray can be enjoyed at any time of day, rain or shine. We like it in the morning, as a gentle reminder to step outdoors, take a quiet moment and reconnect with the natural rhythm of the day.

NHS guidance recommends vitamin D supplementation during the autumn and winter months, whilst those with limited sunlight exposure are advised to consider supplementation throughout the year.

Beyond supplementation: More ways to support your vitamin D

The best source of vitamin D remains exposure to natural daylight. Supplementation simply supports the days when everyday life and the changing seasons make that relationship harder to maintain.

If your goal is to optimise your vitamin D during this time, consider that, as with every other nutrient, Vitamin D does not work in isolation. Vitamin A (found in liver, oily fish and orange-coloured vegetables) and K2 (found in cheese, egg yolks and butter) work synergistically with vitamin D and should be part of your balanced diet.

One egg contains approximately 64IU of vitamin D. A helpful tip is to store your mushrooms on the windowsill, allowing them to continue to benefit from the sun's rays after they’ve been harvested.

You may also want to consider supporting your magnesium intake. Involved in over 300 reactions in the body, Magnesium is critical for our nervous system and stress management. It also helps activate vitamin D in the body, allowing it to support immune defences more effectively. By keeping magnesium levels optimal, you ensure your body can make the most of it during the darker months.