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Vitamin D - intake, deficiency, effect, requirement

Vitamin D is particularly important for healthy bones and our immune system. However, the so-called sun vitamin is also increasingly associated with the development of chronic diseases and is obviously important for our overall health. However, although vitamin D is so important for our well-being, many people do not get enough.

Table of contents:
  • What is vitamin D?
  • Vitamin D - daily requirement
  • When does the body produce enough vitamin D?
  • What are the functions of vitamin D?
  • Vitamin D in food
  • Vitamin D supply and risk groups for a deficiency
  • How does a vitamin D deficiency manifest itself
  • Vitamin D blood levels: How do I recognize a deficiency
  • What should you bear in mind when taking supplements
  • ? Is too much vitamin D harmful?

What is vitamin D?

The term vitamin D stands for a group of fat-soluble compounds (calciferols). Vitamin D3 (cholecalciferol) is found in animal foods, while vitamin D2 (ergocalciferol) is predominantly found in plant-based foods. Strictly speaking, vitamin D is not actually a real vitamin, as the body can produce it itself - given sufficient exposure to sunlight. If UV radiation reaches the skin, vitamin D3 can be formed from the precursor dehydrocholesterol. After absorption or endogenous synthesis in the skin, D3 or D2 is first converted to calcidiol (25-hydroxyvitamin D) in the liver and then to the active form calcitriol (1,25-dihydroxyvitamin D) in the kidneys.

Vitamin D3 often not vegan The cholecalciferol used in food supplements is usually obtained from wool wax (lanolin). However, vitamin D3 can also come from vegan alternatives. The cholecalciferol in our vitamin & mineral products, for example, is obtained from lichen and is therefore vegan.

Vitamin D - daily requirement The German Nutrition Society (DGE) gives an estimated value of 20 µg vitamin D per day for adults (in the absence of endogenous synthesis). The requirement for vitamin D is also often given in international units (IU). 20 µg corresponds to 800 IU. For infants under one year of age, an estimated value of 10 µg (400 IU) is given.

When does the body produce enough vitamin D?

A prerequisite for the body's own synthesis is that sufficient sunlight - more precisely UVB radiation - reaches our skin. This is the case in summer. If you spend enough time outdoors, the body can cover its needs through its own synthesis. But too much sunlight also has its downsides. This is why more and more people are turning to skin creams with UV filters or sunscreens in summer. These prevent UVB rays from penetrating the skin and thus protect against sunburn, but at the same time inhibit vitamin D synthesis. We also spend most of our day indoors - even in summer. It therefore makes sense to take vitamin D supplements in summer too. In addition to the time of year, the time of day, skin color and clothing, age and body weight also influence the skin's own synthesis.

You can read more about this topic in the blog post Why should you take vitamin D supplements in summer?

From October onwards, the days get shorter and the sunlight is no longer intense enough to produce vitamin D. Until spring, the body's own synthesis is not sufficient to cover the requirement. Supplements should therefore be taken during the darker months of the year.

What functions does vitamin D have?

Vitamin D plays an important role in calcium and phosphate metabolism. Calcitriol, for example, is required for the absorption of calcium and phosphate from the intestine and enables the mineralization of our bones. Calcitriol acts as a hormone and influences the formation of various proteins in the target organs by binding to its receptor. It thus also influences the activity of immune cells and the differentiation of epithelial cells in the skin. In addition, a vitamin D deficiency is also associated with the development of diseases such as cardiovascular diseases (e.g. high blood pressure, stroke), multiple sclerosis and cancer. There is still a need for research in this area in order to be able to precisely identify the preventive benefits and mechanisms of action of vitamin D on the development of chronic diseases.

Vitamin D in food

It is difficult to meet requirements through diet, as vitamin D is only found in significant quantities in a few foods. Fatty fish (e.g. herring or mackerel), liver or egg yolk are an exception here. Foods therefore only cover around 10-20% of the daily vitamin requirement. Plant foods contain hardly any vitamin D. Mushrooms are an exception here. Mushrooms or shiitake mushrooms contain small amounts of vitamin D. The vitamin D content of mushrooms can be increased by placing them in the sun or exposing them to UV light. Such vitamin D mushrooms can already be found in some supermarkets. Fortified margarine can also contribute to the vitamin D supply.

According to the results of the National Nutrition Survey II, the daily vitamin D intake from food is well below the recommended intake for men and women in all age groups. A total of 82% of men and 91% of women do not reach the recommended daily intake of vitamin D. A study by Chan et al. shows that there is no correlation between diet and vitamin D intake. Vegetarians, vegans and mixed dieters are equally affected by insufficient vitamin intake.

Vitamin D supply and risk groups for a deficiency

Vitamin D is considered a critical nutrient. This means that a high proportion of the population does not have an adequate supply. According to data from the Robert Koch Institute, 56% of German adults are insufficiently supplied with vitamin D. Of these, 15.2% have a deficiency.

Vitamin D deficiency can affect all population groups, but some risk groups are particularly susceptible:

  • People who spend little time outdoors or who cover their bodies completely (e.g. for religious reasons) when they go outside
  • Infants and young children (as they should not be exposed to the sun)
  • Certain illnesses (chronic gastrointestinal, liver or kidney disease)
  • Taking certain medications (e.g. anti-epileptic drugs, cytostatics, barbiturates)
  • Older population groups, as the skin's ability to synthesize its own substances decreases with age
  • People with strong skin pigmentation: the lighter the skin, the more vitamin D is produced and vice versa
  • People who are very overweight (BMI>30 kg/m2), as they have less efficient vitamin D synthesis than people of normal weight
  • To ensure an adequate supply of vitamin D, year-round supplementation is recommended for these risk groups. It may also be advisable to take higher amounts than the estimated values recommended by the DGE (with the exception of infants and children)

Caution with impaired fat digestion

Vitamin D is one of the fat-soluble vitamins and is absorbed from the intestine together with dietary fat. Diseases that disrupt fat digestion (e.g. coeliac disease, pancreatic insufficiency) can therefore also cause a vitamin D deficiency.

How does a vitamin D deficiency manifest itself? An inadequate supply of the sun vitamin is particularly evident in our bones. Characteristic of a vitamin D deficiency in childhood is rickets, a deformation of the skeleton as a result of insufficient bone mineralization. If this occurs in adulthood, it is referred to as osteomalacia (demineralization and remodelling processes of the bone). An inadequate supply of vitamin D also contributes to the development of osteoporosis.

However, non-specific symptoms such as an increased susceptibility to infections, depressive moods, reduced muscle strength and the presence of listlessness and tiredness can also indicate a vitamin D deficiency.

Vitamin D blood levels: How do I recognize a deficiency?

To determine the supply status of vitamin D, the level of calcidiol (25-hydroxyvitamin D/25-OH-D) is determined. The following serum values provide an overview of the supply status:

  • <30 nmol/l or <12 ng/ml = deficiency
  • 30-50 nmol/l or 12-20 ng/ml = insufficient supply
  • ≥50 nmol/l or ≥20 ng/ml = sufficient supply
  • >400 nmol/l or >160 ng/ml = oversupply

What should you bear in mind when taking dietary supplements

Most vegan food supplements contain vitamin D3. Some studies suggest that vitamin D3 is more effective than plant-based D2. However, this has not been sufficiently proven and some studies also suggest the exact opposite or show no difference in terms of effectiveness. It is important to know that many vitamin D3 supplements are not vegan. However, there is also plant-based D3, which is obtained from lichen.

Vitamin D is one of the fat-soluble vitamins and should therefore be taken together with a high-fat meal. It is also recommended to take it together with vitamin K, as the two vitamins have a synergistic effect. You can find out more about why you should take vitamin D and K together in the blog post "O3-D3-K2 Vegan - Why a combination supplement makes sense".

Nutri-Plus vitamin D combination products

Whether in our micronutrient combinations (e.g. Immune and Vegan Essentials) or in our D3-K2 combination products (D3-K2 and O3-D3-K2): We use plant-based vitamin D3 in all products.

Is too much vitamin D harmful?

It is not possible to overdose on vitamin D via conventional foods or self-synthesis through the skin. However, excessive intake of food supplements can lead to an overdose. In the case of vitamin D intoxication, increased calcium is absorbed from the intestine and released from the bones (hypercalcemia). This can lead to organ damage (especially to the kidneys). According to the EFSA (European Food Safety Authority), adults should therefore not exceed the maximum amount (UL = Tolerable Upper Intake Level) of 100 µg per day in the long term.

Robert Koch Institute. Answers from the Robert Koch Institute to frequently asked questions about vitamin D; as at 25.1.2019. Max Rubner Institute, Federal Research Institute of Nutrition and Food. Results Report, Part 2, National Consumption Study II, The nationwide survey on the nutrition of adolescents and adults. 2008. J. Chan et al. Serum 25-hydroxyvitamin D status of vegetarians, partial vegetarians, and nonvegetarians: the Adventist Health Study-2. Am J Clin Nutr. 2009;89(5):1686S-1692S. European Food Safety Authority. Maximum Intake Values for Vitamin D and Calcium Reviewed. Published July 27, 2012.