Vitamin D - what is it?
Vitamin D is one of the fat-soluble vitamins: fat-soluble means that the body needs some fat for absorption, just like with vitamins A or E. This is why you can usually buy vitamin D supplements dissolved in oil. If this is not the case, you can simply take vitamin D with some fat or fatty foods like a piece of cheese.
The prerequisite for sufficient vitamin D production in the body is enough sunlight exposure on our skin. If this is given, the body can produce about 80 - 90% of the required vitamin itself. The remaining 10 - 20% of your vitamin D supply can be covered through your diet.
Vitamin D and the hormone: Calcitriol
The body converts the self-produced vitamin D into a hormone called calcitriol. Accordingly, vitamin D is actually more of a hormone precursor, comparable to tomatoes as an ingredient for a salad, which represents the hormone.
We can grow tomatoes (the hormone precursor vitamin D) in the garden, but we have to prepare the salad (the hormone calcitriol) ourselves. Calcitriol is the biologically active form of vitamin D, meaning the form in which the body can actually use vitamin D for further processes.
Vitamin D - What makes it so special?
We produce the majority of our required vitamin D ourselves with the help of the sun. So, strictly speaking, vitamin D is not a true vitamin at all:
By definition, vitamins are compounds that the body cannot produce in sufficient quantities itself. Therefore, we must consume them through food.
As you have read, this is not entirely true for vitamin D, as the majority of the supply is covered by self-production.
It is typically characteristic of vitamins that they are essential nutrients for us. This means that we must consume them with food, such as vitamin B12 or vitamin E. The body usually cannot produce them itself.
The group of D vitamins
As mentioned at the outset, vitamin D refers to several vitamins or chemical compounds. It is, so to speak, a collective term for various forms of a group, which we would like to explain to you below.
Attention! There are a few chemical terms that might seem complicated at first, but they are not that wild:
Cholecalciferol is an important part of this group - you know it better as vitamin D3.
To produce the biologically active form calcitriol, the body needs exactly this vitamin D3. For simplification, you can think of our salad, the hormone, for which we need different ingredients. Vitamin D3 is again an ingredient here. In the liver and kidney, cholecalciferol can be converted into calcitriol, the active hormone. It sounds complicated at first, but don't worry, you'll get it soon.
Besides vitamin D3, there is also vitamin D2, also called ergocalciferol. The body further converts ergocalciferol into the more usable form cholecalciferol, vitamin D3.
So imagine vitamin D2 as a tomato seed, while vitamin D3 is already the grown tomato, with which we can do more than with a single seed.
Vitamin D: Daily requirement
The daily vitamin D requirement is approximately 20 micrograms per day. This recommendation applies from the first year of life and equally to all subsequent age groups.
During the first year of life, about half the amount of vitamin D, 10 micrograms per day, is recommended for babies.
The recommendation comes from the German Nutrition Society (DGE) and refers to a vitamin D intake of 20 micrograms per day in the absence of endogenous synthesis. This means that the body's own production of vitamin D is prevented by insufficient sunlight. This is usually the case, for example, during the German winter months.
How is vitamin D stored in the body?
From our vitamin D3 tomato, the body can produce calcifediol - the storage form of vitamin D. The body's own stores are primarily located in our fat and muscle tissue.
While you can replenish your stores well in summer in the garden, on the balcony or at the swimming lake, the body draws on these during the winter months. The stores are accordingly large. However, if you have spent too little time outdoors or, for example, in the office in spring and summer, it can become tight by the end of winter at the latest. In this case, diet can help or support through vitamin D-containing food supplements.
The different forms of Vitamin D
Here you can see the mentioned forms of Vitamin D at a glance for differentiation.
This way, in the future, you'll be able to better classify the terms when reading an article or an ingredient list.
| Cholecalciferol | Vitamin D3, formed from Vitamin D2 |
| Calcitriol | The biologically active form of Vitamin D, hormone, formed from Vitamin D3 |
| Ergocalciferol | Vitamin D2, precursor to Vitamin D3 |
| Calcifediol | Storage form of Vitamin D, also found as 25-hydroxyvitamin D or 25-OH-vitamin D, formed from Vitamin D3 |
Our skin and vitamin D
When you feel the pleasant warmth of the sun's rays on your skin, your body is probably producing vitamin D at that moment.
Our skin, as our largest organ, is therefore the site of vitamin D production. For this, the UVB rays emanating from the sun are necessary, which, however, should not be confused with the harmful rays of a solarium. These rays must hit your skin directly. So it's not enough if you try to catch some sun through a pane of glass.
For all couch potatoes and workaholics: Put on your shoes and get out into the sun as soon as it shines and an opportunity for a little sunbath presents itself!
In Central Europe and Germany, however, the sun is too weak for sufficient vitamin D production, especially in winter. Apart from that, we would also have to sit in the sun with bare arms and legs in winter to absorb enough sun at all.
Vitamin D - how much time in the sun is necessary?
In Germany, the following guideline applies: In our latitudes, it is usually sufficient if you spend about 10 - 25 minutes a day in the sun for half of the year.
Approximately a quarter of your body surface should be exposed to the sun. This means that parts of the legs, arms, hands, and face are in direct sunlight.
Sunlight is most intense daily between 12 PM and 3 PM. During this time, you should spend a maximum of 25 minutes unprotected in the sun. This also applies if it is a bit cloudy. Even then, UVB rays can reach our skin in spring and summer and form vitamin D.
Particularly light-skinned and light-haired individuals should aim for shorter periods of 10-15 minutes a day, especially during the summer months of June, July, and August.
Of course, even here, despite the importance of vitamin D production: for longer sun exposure, always protect your skin with sunscreen! Although this inhibits vitamin D production, it protects our skin from dangerous sunburn.
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How important is vitamin D for the body?
First and foremost, vitamin D is important for our bones. Calcitriol, our active vitamin D, supports the formation and maturation of our bone stem cells.
Vitamin D and other body functions
Vitamin D can do much more for our body than just support and regulate bone and tooth formation. A sufficient vitamin D level in the body is required for maintaining the following basic functions:
- Muscle function
- Immune system
- Cell division
- Calcium absorption in the intestine
- Bone and tooth formation, general bone health
Vitamin D and calcium
Vitamin D is also closely related to calcium balance: It regulates calcium absorption in our intestine and supports the incorporation of calcium into bones.
This process is called mineralization, which makes our bones firm and strong. The same applies to strong teeth, for which calcium and phosphate are needed. Vitamin D also makes an important contribution here.
Vitamin D research
Most likely, Vitamin D has much more to offer than previously known. However, scientific evidence for many of Vitamin D's mechanisms of action is still pending.
Vitamin D research is currently lagging particularly in the following areas:
- Importance for the cardiovascular system
- Positive impact on vascular diseases
- Protection against cancer
- Protection against neurological diseases
- General immune system strengthening, especially in autoimmune diseases
- Effect on muscles
- Effect on our psyche, e.g., effect on depression
Although vitamin D has been researched for decades, new exciting mechanisms of action and functions can always be identified. Future research therefore seems very promising! That makes the short daily sunbath even more appealing, doesn't it?
Which foods contain Vitamin D?
Nature has also come up with many good things when it comes to Vitamin D.
Because we need fat for the physical absorption of vitamin D, vitamin D is found primarily in fatty foods such as dairy products (e.g., Gouda) or fatty fish such as herring.
Even if diet only contributes a small amount to our vitamin D balance:
It is still advisable to pay attention to vitamin D-rich foods and regularly include them in your diet. In this way, you can actively support your body's own vitamin D production and help it on gray days without sunlight.
This is how people, such as those in Norway, who sometimes don't see the sun for months, also support their vitamin D balance. Here, vitamin D-rich foods, especially fatty fish, are regularly on the menu.
Which foods are particularly rich in vitamin D?
The following foods contain the specified amount of vitamin D in micrograms per 100g:
- Gouda 1.3
- Processed cheese (45% fat in dry matter) 3.1
- Emmental 1.1
- Eel 20
- Herring 25
- Salmon 16
- Beef liver 1.7
- Chicken egg 2.9
- Raw mushroom 1.9
- Raw chanterelle 2.1
- Butter max. 2.5
- Vegetable margarine 2.5
Vegan diet and Vitamin D
As you can see, vitamin D is primarily found in animal products.
In plant-based foods, you will only find vitamin D in the less available form D2 (you can think of the comparison with tomato seeds here). In fruits and vegetables, vitamin D is only present in very small amounts. An exception is edible mushrooms like champignons or chanterelles.
We recommend that people who follow a vegan diet pay particular attention to their food choices, especially during the dark winter months. If necessary, an additional check of vitamin D levels by a doctor is advisable.
How does a vitamin D deficiency occur?
A vitamin D deficiency usually occurs when too little sun falls directly on the skin.
Too little means that we cannot maintain the recommended times of 10 - 25 minutes a day in the sun. This primarily refers to the half of the year when we have the opportunity to replenish our vitamin D stores.
What causes vitamin D deficiency?
The following causes can lead to a vitamin D deficiency:
- Too little time in the sun: This can affect, for example, elderly people who no longer have the opportunity to go outside regularly. However, it can also affect people of all ages who sit in front of the PC from morning to evening due to home office. Just like couch potatoes, they spend too little time outdoors and in the sun.
- Disruption of vitamin D metabolism due to medication intake, e.g., medication for epilepsy.
- In case of renal insufficiency or nephrotic syndrome, due to excessive excretion of vitamin D via the kidneys
- Impaired physical absorption and utilization of vitamin D in the intestine, e.g., in case of gluten intolerance, intestinal diseases, and gastrointestinal surgeries
- Lack of intake through diet, e.g., in people who eat a strictly plant-based diet. This can be true despite the less significant influence of diet on our vitamin D balance.
How do I recognize a vitamin D deficiency?
As is often the case with a vitamin deficiency, it is not easy to identify the source of physical symptoms. The signs of a vitamin D deficiency also appear rather unspecific and diverse at first. Affected individuals initially report the following physical complaints:
- Frequent infections
- Fatigue, lack of energy
- Increased hair loss
- Weak muscles
- Muscle or limb pain
- Headaches
- Nearsightedness
Later, the following more severe effects may also occur:
- Neuromuscular hyperexcitability: Migraines, muscle cramps, and paresthesias, e.g., in the fingers or lips
- Disorder of bone mineralization, noticeable through bone pain: This is called rickets in children; in adulthood, we speak of osteomalacia.
Vitamin D and food supplements
It is possible to supplement vitamin D through food supplements in addition to diet. So-called vitamin D preparations are suitable for individuals whose insufficient supply has been medically confirmed.
Alternatively, food supplements can help if the supply of vitamin D cannot be ensured through diet or the body's own production. This may be the case, for example, with certain medical conditions.
If you feel unsure or are considering taking additional vitamin D supplements, your doctor can help you. A blood test can provide information about your actual vitamin D level in the body and your corresponding needs.
Conclusion: What can I do for my vitamin D balance?
Finally, we give you some practical tips on what you can do to actively support your vitamin D balance and prevent a deficiency.
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Time outdoors:
Take advantage of spring and summer to spend time outdoors and in the sun to replenish your vitamin D stores!
Depending on your skin type, just 10 - 15 minutes a day in the sun is enough to avoid a vitamin D deficiency - and that for about half the days of the year! Even if it's a bit cloudy, our bodies can absorb UVB rays and produce vitamin D. -
Vitamin D-rich foods:
Especially in the darker winter months, include vitamin D-rich foods in your diet. Especially fatty foods like cheese and fish, as well as mushrooms, provide you with vitamin D.
Ideally, eat fatty fish like herring once or twice a week. -
Bring the sun into your home:
People who work a lot or have to spend most of the day indoors can also benefit from a daylight lamp to prevent a vitamin D deficiency.
Get advice at an electronics store on which lamp can really help. -
To be on the safe side:
If you are concerned that your time outdoors is not sufficient for a healthy vitamin D level in your body, consult your doctor.
They can perform a blood test and, if necessary, support you with vitamin D supplements.
All our articles are written by nutritionists and reviewed by subject matter experts for quality of content.
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