True Vitamin D3 K2 origin story: Vitamin D designed for modern living

Here, Dr Jenna Macciochi, Immunologist and Director of Science and Innovation, explores the seasonal biology of vitamin D, taking us from the farmers of Orkney to the realities of our increasingly indoor modern life, to explain why we created True D3 + K2, our vegan vitamin D ritual spray to help bridge the sunshine gap between our ancient biology and our modern way of life.

Seasonal signals: How the seasons shaped our biology

As we move towards winter in the UK, the signals are everywhere: darker mornings, leaves turning, and the light beginning to leave the day a little earlier.

Around this time each year, another seasonal signal arrives. Between October and early March, sunlight here does not carry enough UVB for our skin to make vitamin D. This is why the NHS advises that everyone should consider taking a daily vitamin D supplement during autumn and winter (1).

It always makes me wonder: if vitamin D is so important to human health, and our primary natural source is sunlight, what did humans do before supplements?

When I began digging into the research, the answer was not that our ancestors had somehow perfected their vitamin D status, but something altogether more interesting.

Human biology evolved in relationship with the seasons: not just changing light, but changes in temperature, food availability, activity and exposure to the living world. For our ancestors, noticing and responding to these changes was not a wellness practice. It was necessary for survival. 

Vitamin D is a beautiful example of how our biology remains in conversation with the seasons.

A nutrient written in sunlight: What is vitamin D, and what does it do?

Vitamin D is unusual. Although we call it a vitamin, once activated in the body is functions as a hormone. And that matters when we think about what vitamin D actually does.

Vitamins play many roles in supporting biological processes, for example, acting as cofactors that help enzymes and chemical reactions work properly. Hormones are better thought of as chemical messengers: they bind to receptors and carry instructions to cells and tissues to change what they are doing.

Vitamin D can take those instructions right into the nucleus of our cells and instruct the machinery that turns genes on and off. Our skin produces vitamin D3 when exposed to UVB light. 

It is then transformed first in the liver into 25-hydroxyvitamin D, or 25(OH)D. This is the form we usually measure in a vitamin D blood test because it circulates in the blood long enough, with a half-life of around two to three weeks, to give us a useful picture of vitamin D status.

From there, it can be converted, primarily in the kidneys, into 1,25-dihydroxyvitamin D, its active hormonal form. This has a much shorter half-life, measured in hours rather than weeks, and is tightly regulated by the body. This active form binds to the vitamin D receptor, or VDR, which acts inside the nucleus to influence which genes a cell reads and which biological instructions it acts upon. This is why vitamin D has far-reaching effects on our health.

This is why vitamin D is so much more interesting than simply a nutrient we get from sunlight: once activated, it becomes a biological signal capable of changing what our cells do.

Vitamin D was first identified through the story of rickets and bone health, but its role is not confined to the skeleton. Vitamin D contributes to the maintenance of normal bones and teeth, normal muscle function and the normal function of the immune system. It also contributes to normal blood calcium levels and the normal absorption and use of calcium and phosphorus.

Which brings us back to the seasons. If this sunlight-derived nutrient reaches so widely into our physiology, what happens when winter sunlight lessens our ability to make it? And what did humans do before supplements?

Measuring the sun: How humans supported vitamin D before supplements

The answer is not that our ancestors somehow perfected their vitamin D status. Nor is it simply that they spent more time outdoors (although it's likely that their way of life necessitated this comparatively). Human biology evolved in relationship with seasons, with changing light, temperature, food availability and activity. Vitamin D still carries the imprint of one of those changes, the turning of the light in autumn.

Before we measured vitamin D, we measured the sun. Long before we could measure vitamin D in blood, humans measured the sun. We watched where it rose and set. We followed shadows and built calendars, sundials and monuments around its movement. Our ancestors did not know about ultraviolet B light, vitamin D receptors or how to measure blood 25-hydroxyvitamin D. But they understood something more fundamental: the light changed, and life changed with it.

Seasonality was not something they tracked on an app. It was woven into the architecture of everyday life. Reading the seasons shaped when people planted, harvested, preserved food and prepared for winter. Their survival depended upon responding to environmental signals that many of us can now easily insulate ourselves from.

We have not lost our seasonal biology. But we may have lost some of the everyday practices that kept us in closer conversation with it.

Why might vitamin D drop in winter? Latitude and an ancient rhythm

Our vitamin D status with which we enter winter is partly shaped by what happened during the brighter months before it.

Yet many of us now spend those sunny months working indoors. Sensible sun-safe practices also reduce UV exposure (as they are intended to do), but together these changes in lifestyle can reduce the opportunities our skin has to make vitamin D, even during the part of the year when light allows.

But here is the interesting part: seasonal vitamin D decline is not purely a modern problem. A fascinating 2025 study led by researchers at the University of Aberdeen measured vitamin D in the hair of people living in Aberdeen today and in preserved hair from someone buried there during the 16th or 17th century. Both the modern and historical hair showed vitamin D rising during summer and falling in winter (2).

It is only one archaeological individual, so we cannot extrapolate from it to an entire ancestral population.

But it gives us something intriguing to think about. The winter decline we see today may not just be a modern aberration. It is an old rhythm of life at a northern latitude. What has changed is the context in which that old rhythm now plays out. Many of us spend much of the brighter part of the year indoors, reducing our opportunities to make vitamin D during the very months when the light allows it.

True D3+ K2: A vitamin D made for daily ritual 

Today, of course, we don't have to read the changing light to understand what is happening to our vitamin D. We can measure it in blood, we understand much more about its biology, and in the UK we have clear seasonal public-health guidance.

But knowing what may support us and consistently doing it are two different things.

We saw a glimpse of this when we asked 756 members of our Inner Circle community about their knowledge, attitudes and habits around vitamin D. Awareness was already high, and 72% told us they took vitamin D at least occasionally, yet only 60% took it regularly.

That gap between knowing and doing is something I think about a lot in health. Information matters, but it still has to survive contact with everyday life.

And that became part of our thinking when we created True D3 + K2. We wanted a foundational formula with a clearly defined daily amount, but also one that was simple and distinctive enough to return to each day through the darker months, and year-round where appropriate.

Habits rely on cues: a taste, a scent or a familiar moment in the day can make a behaviour easier to remember and repeat. That thinking shaped not just what went into True D3 + K2, but the ritual of taking it.

+ A once-daily, four-spray serving that is easy to add to an existing routine

+ A distinctive rosemary-and-peppermint flavour that provides a fresh sensory cue

+ 50μg (2,000 IU) of vegan vitamin D3 per daily serving

+ 50μg of vitamin K2 as MK-7, paired with vitamin D for their complementary authorised roles in maintaining normal bones

+ An MCT oil base, providing a suitable carrier for two fat-soluble nutrients

+ A three-bottle, three-month option, designed to support consistency over time

The best formula in the world cannot help if it never becomes part of your life. With its fresh natural rosemary extract and peppermint leaf oil, True D3 + K2 turns daily supplementation into a small, refreshing ritual, designed to be returned to through every season

Formulating with biology and behaviour in mind

The formulation itself follows the same thinking. We chose vegan vitamin D3, the same form our skin naturally produces in response to UVB light, providing 50μg (2,000 IU) in a once-daily four-spray serving.

We paired it with vitamin K2 as MK-7 because vitamin D and vitamin K both have complementary roles in the maintenance of normal bones, and brought the two fat-soluble nutrients together in our beautiful True MCT oil base.

Of course, what goes into a formula matters. But I also think about what happens once that formula leaves our hands and has to find a place in someone's actual life.

Humans have always used ritual to give shape to the things we return to. We have built rituals around food, light, gathering and the changing seasons — particularly the transition into the darker months. They create rhythm and repetition, but also meaning: small ways of marking what matters and remembering to return to it.

That thinking found its way into the formulation too. Rosemary and peppermint aren't simply there for flavour. Their fresh taste and aroma make the experience distinctive, creating a sensory cue that can become associated with a familiar moment in the day.

Perhaps that is what a modern ritual can be: something small and intentional that helps us stay in conversation with our biology, even when the rhythms of modern life make those signals easier to miss.

Vitamin D designed for every season

Vitamin D is often treated as a winter-only conversation. For many people in the UK, autumn and winter are the most relevant times to supplement because sunlight is not usually sufficient for skin synthesis. But season is only part of the picture.

The NHS advises some people to consider vitamin D throughout the year, including those who spend very little time outdoors, usually cover most of their skin or have darker skin, including people with African, African-Caribbean or South Asian heritage.

Summer does not automatically guarantee sufficient vitamin D. Skin pigmentation, age, clothing, sunscreen use, time outdoors and individual biology all influence how much a person makes.

The aim is not to fear the sun, seek excessive UV exposure or imagine that a supplement can replace outdoor life and a varied diet. It is to recognise that biology only makes sense in context, and that geography, season and modern behaviour do not always line up neatly.

Closing thoughts

Vitamin D tells a much bigger story than that of a single nutrient.

It tells us that our bodies do not exist separately from the world around us. They remain in conversation with light, season, food, movement and place.

Modern life did not create the sunshine gap. The Aberdeen research suggests that seasonal vitamin D decline existed centuries ago. But indoor living may compound an old biological constraint created by latitude and season.

For me, True D3+K2 represents something pragmatic: noticing where our biology and our lives no longer quite meet, and thoughtfully bridging the gap.

And perhaps that is the bigger idea behind True D3 + K2. Our biology is ancient. Our lives are modern. Good formulation should understand both.

1. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d

2. https://www.abdn.ac.uk/news/24047/