Supplements & Sun: Vitamin D in Summer

It is July, you come back from the lake tanned – and wonder whether the vitamin D capsule is actually superfluous now. Short answer: in high summer, when you are regularly in the midday sun with uncovered arms and legs, your skin can form so much vitamin D that a supplement often takes a back seat. Whether this applies to you, however, depends on a surprisingly large number of factors – from sun protection through skin type to the simple question of how much time you really spend outdoors. This guide shows you how sun and supplement interact in summer and when continuing to supplement is worthwhile nonetheless.

The most important points at a glance

• Vitamin D contributes to normal muscle function, to the maintenance of normal bones and teeth and to a normal function of the immune system.
• With sufficient midday sun, the skin in summer can form large amounts of vitamin D itself – the need for a supplement is then often lower.
• The body's own formation varies greatly: the position of the sun, skin coverage, sun protection, skin type and length of stay outdoors all play a part.
• Vitamin D is fat-soluble and is best taken with a fat-containing meal; the time of day is secondary.
• Whether and how much you supplement in summer is most reliably clarified by your blood level (25-OH vitamin D).

How your skin makes vitamin D from sunlight

The mechanism is elegant: in your skin sits a precursor of the vitamin, 7-dehydrocholesterol. When high-energy UV-B radiation hits it, it is converted into previtamin D, which matures via intermediate steps in the liver and kidney into the active form. Vitamin D is thus, strictly speaking, less a "vitamin" than a hormone precursor that your body produces itself when there is enough light. This is exactly why it is called the "sunshine vitamin" – and exactly why summer is the season in which your body's own laboratory runs at full speed.

How much actually arises, however, is highly individual. These factors are decisive:

• Time of day and position of the sun: UV-B reaches the skin only when the sun is high. Around midday (about 11 a.m. to 3 p.m.) formation is most productive – in the morning and evening sun hardly at all.
• Skin coverage and sun protection: clothing and sunscreen filter UV-B strongly. This protects against sunburn – but slows down vitamin D formation. A contradiction that has to be balanced consciously.
• Skin type: melanin acts like a built-in light protection. Darker skin types need considerably more sun time for the same amount of vitamin D than very light ones.
• Age: over the years the skin's formation capacity declines – one reason why older people are not automatically "topped up" in summer.
• Length of stay: anyone who sits in an air-conditioned office and only walks to the car forms little despite high summer.

The basic connection between light and vitamin D is explored in depth by the article The dark season, light and vitamin D – the considerations there simply apply in reverse in summer.

Why many continue to supplement in summer anyway

One might think the topic is settled in summer. In practice it often is not – and this has tangible everyday reasons. Many people today live largely "indoors": office, car, flat. Anyone who consistently uses sunscreen with a high sun protection factor (dermatologically absolutely sensible) considerably reduces formation. And anyone who avoids the blazing sun in summer – for good reason – thereby also forgoes the main source. That is why people with an office job, a darker skin type or in older age in particular keep an eye on their supply in summer too.

The second reason is the storage idea: vitamin D is fat-soluble and can be stored in the body. A well-filled store at the end of summer is the cushion you draw on in winter. Anyone who does nothing at all over the summer and gets little sun starts into the dark season with a half-empty tank. How to think dosage and blood level together over the year is described in detail by Vitamin D: dosage, blood level and winter.

What research is investigating

The role of vitamin D as a nutrient is textbook knowledge: it helps regulate the calcium and phosphate balance, is indispensable for bone metabolism and intervenes in the function of immune and muscle cells. Beyond these established fundamentals, research intensively investigates how vitamin D status changes over the seasons and which factors control the body's own formation in detail. It is researched, for example, how strongly skin type, geographical latitude and sun protection behaviour influence summer status. Much of this is still the subject of ongoing investigations – what is established above all is the basic finding that in our latitudes the skin can form appreciable vitamin D only in the summer half of the year.

Authorised statements about vitamin D

These functions are officially recognised and may be clearly named. Vitamin D contributes:

• to the maintenance of normal bones, teeth and muscle function,
• to a normal absorption and utilisation of calcium and phosphorus,
• to a normal calcium level in the blood,
• to a normal function of the immune system as well as
• to cell division.

These statements apply with a sufficient supply – they describe normal body functions and are not a promise of cure.

Timing: when to take vitamin D in summer?

Because vitamin D is fat-soluble, what counts is less the time of day than being accompanied by some dietary fat. Take it with a main meal that contains fat – whether breakfast with yoghurt and nuts, lunch with olive oil in the salad or dinner hardly matters for absorption. Anyone who deliberately doses lower in summer (because the sun helps out) benefits especially from coupling the intake to a fixed habit, so that it does not gradually slip into oblivion.

Many combine vitamin D with vitamin K2; background is provided by Vitamin D and K2 together. The general rules on interaction with food are explained by Nutrients before or after eating, and how long it takes for the status to change you can read in How long until vitamin D takes effect.

How much sun does the skin actually need?

There is no fixed number of minutes that applies to everyone – and anyone who claims one is oversimplifying. How much sun your skin needs for relevant vitamin D formation depends on the skin type, the position of the sun (time of day, season, geographical latitude) and the uncovered skin area. As a rough rule of thumb: shorter, regular stays in the midday sun with uncovered forearms and face are more productive than rare, long sunbathing – and considerably gentler on the skin. What matters is the balance: enough sun that formation is stimulated, but without risking sunburn, because that damages the skin. Anyone who cannot reliably manage this balance in everyday life – for example because of an office job or sensitive skin – keeps their supply stable rather via diet and a targeted supplement. How to approach this in interplay with little daylight is shown by Nutrients with little sunlight.

Summer vs. winter: the annual course at a glance

For whom the summer look is especially worthwhile

Not everyone has to deal intensively with vitamin D in summer – but for some groups the attention pays off especially. These include people whose everyday life is spent predominantly indoors (office, home office, shift work), people with a darker skin type, older people whose skin formation declines, as well as everyone who, for good reasons, consistently uses sun protection. Anyone who avoids the blazing sun also forgoes the main source thereby. For these groups it can be sensible not to lose sight of the supply even in summer – in case of doubt via a blood level. Anyone who is out and about a lot or travelling will find additional guidance in Nutrients on long-haul travel.

Honestly assessed

What is established: the skin forms vitamin D in summer with sufficient UV-B radiation, and this contribution is considerable. Equally established is that this formation varies extremely from person to person. That is why there is no blanket rule that "in summer you need nothing". For one person it is true, for another not – depending on skin type, lifestyle and sun behaviour. What one cannot reputably say: that a certain amount of sun time guarantees a certain blood level in everyone. Anyone who wants to know for sure measures. A 25-OH vitamin D value is the only reliable guide – especially if you are considering pausing the supplement in summer.

Matching products from Scheunengut

Vitamin D preparations – individually or as a combination with K2 – you will find in the category Vitamin D. The matching partner K2 is stocked by the category Vitamin K, and a broader overview is offered by the category Vitamins. If you think about your supply holistically in summer, it is also worth taking a look at the category Immune system. In-depth guides: Dosage, blood level & winter, Vitamin D3 + K2, Drops or capsules, Light & vitamin D and Vital substances from 50.

Frequently asked questions (FAQ)

Can I cover my vitamin D requirement in summer through the sun alone?

With sufficient midday sun and uncovered skin, the body's own formation in summer can cover a large part of the requirement. Whether it really is enough for you, however, depends on skin type, sun protection and time outdoors. This can be reliably clarified only via the 25-OH vitamin D blood level – not via a feeling.

Should I skip the vitamin D capsule in summer?

It depends. Anyone who is in the sun a lot and regularly often needs less in summer or pauses. Anyone who works predominantly indoors, consistently uses sunscreen or has a darker skin type, by contrast, often continues to supplement. It is best to base the decision on a measured blood level and medical advice rather than stopping across the board.

Does sunscreen slow down vitamin D formation?

Yes. Sun protection filters UV-B and thereby reduces vitamin D formation in the skin. That is no reason to forgo protection – sunburn damages the skin. Many resolve the conflict of aims by keeping an eye on their supply via diet or a targeted supplement and not compromising skin protection.

Why is the vitamin D store important at the end of summer?

Vitamin D is fat-soluble and is stored. A well-filled store at the end of summer is the cushion the body draws on in winter, when the skin can barely form any more. That is why it is worth not losing sight of the supply over the summer entirely.