11 Sources of Vitamin D for Your Health

Table of Contents:

• Vitamin D: The Truth Behind Its Classification as a Vitamin
• Reasons Why Vitamin D Is Classified as a Vitamin
• Reasons Why Vitamin D Is Deficiency in Our Body
• Determining the Optimal Type of Vitamin D
• The Optimal Daily Intake of Vitamin D.
• Sources of Vitamin D: What Foods Contain It?
• Is It Possible to Meet Your Vitamin D Needs Through Diet Alone?
• The Differences Between Vitamin D Supplements and Vitamins complexes

In this article, you will learn about the following:

• It is believed that vitamin D should not be classified as a traditional vitamin. In fact, it can be classified as a hormone, as it is synthesized in the body under the influence of sunlight. This process makes it unique among other vitamins, which are typically obtained exclusively through food. Vitamin D plays an important role in regulating calcium and phosphorus metabolism, which, in turn, is critical for bone health and the immune system. Thus, its importance for the human body cannot be overestimated, despite the difference in its nature compared to classic vitamins.
• Vitamin D deficiency can be explained by several factors. Firstly, the main source of this vitamin is sunlight, and many people do not get enough sunlight, especially during the winter months or in regions with low solar activity. Secondly, our lifestyle, which includes spending a lot of time indoors, also reduces the level of sun exposure on the skin.

  Furthermore, some factors, such as age, certain medical conditions, or the use of sunscreens, can interfere with the synthesis of vitamin D. Dietary habits also play a role: many foods rich in this vitamin are absent from the modern human diet. Thus, vitamin D deficiency is becoming a common problem that requires attention and possibly supplementation to maintain normal levels of this important substance in the body.

• Which type of vitamin D is most appropriate?
• The amount of vitamin D the body needs depends on various factors, including age, gender, physical activity level, and overall health. On average, most people are recommended to get between 600 and 800 international units (IU) of vitamin D per day. However, for some groups, such as the elderly or people with certain medical conditions, the need may be higher. It is always a good idea to consult a doctor to determine your individual needs.
• Which foods contain large amounts of it?
• Can you fully meet your vitamin D needs through diet alone?
• Vitamin D supplements and vitamin preparations each have their own unique characteristics and purposes. The main difference is that dietary supplements are typically intended to supplement the diet and may contain not only vitamin D but also other elements that promote overall health. They are often used to address vitamin deficiencies in the body, which can occur due to insufficient dietary intake or absorption problems.

  On the other hand, vitamin preparations can typically be more specialized and focus on specific vitamins or minerals. They may include higher dosages of active ingredients and are often used to treat specific conditions or diseases associated with vitamin deficiency.

  Thus, while both types of products may contain vitamin D, their functions and composition can differ significantly, making each suitable for different purposes and needs of the body.

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Vitamin D: The Truth About Its Classification as a Vitamin

Our bodies produce vitamin D on their own. The process begins when the sun's ultraviolet rays activate it in the skin, after which it undergoes conversion in the liver and kidneys. Interestingly, from a biochemical point of view, vitamin D is not a vitamin in the traditional sense of the word; in its properties, it is more like a hormone. Let's compare its functions with those of other vitamins:

Reasons why vitamin D is classified as a vitamin

Because the active form of vitamin D functions as a hormone, it is commonly referred to in scientific literature as the D-hormone.

Vitamin D has an interesting historical background. In 1922, American scientist Elmer Werner McCollum extracted it from fish oil, believing that it could prevent and treat rickets in children, as well as strengthen their bone and cartilage structure. McCollum assigned this substance the chemical name "calcitriol" because it helped increase blood calcium levels. However, he also called it vitamin D because he found the compound in foods, believing it to be a true vitamin (the human body's ability to produce it on its own was discovered later).

Today, researchers have found that vitamin D is present in more than 40 different tissues [2], including:

• helps reduce excess weight [3];
• helps improve depressive disorders [4];
• helps strengthen tooth enamel and improve oral health [5];
• reduces inflammation in tissues [6];
• protects cells from the negative effects of free radicals [7];
• strengthens the immune defense against infections [8];
• helps increase the synthesis of female sex hormones [2].

In addition, adequate levels of calcitriol significantly reduce the likelihood of many diseases and infections [9].

Causes of Vitamin D Deficiency in Our Body

About 1 billion people worldwide suffer from a lack of vitamin D, which is commonly called hypovitaminosis D. This is surprising, since it is known that this vitamin is synthesized in the skin under the influence of sunlight. Ultraviolet rays, in fact, cover approximately 80% of the body's needs for vitamin D.

Vitamin D can be considered the most "problematic" for a number of factors. Its formation in the skin is influenced by:

• Geography. Medium-wave ultraviolet rays (UVB) are necessary for the synthesis of vitamin D, known as "sunshine". However, these rays are not evenly distributed across the planet - their amount decreases with distance from the equator, which leads to a decrease in UVB levels [12], [13]. Due to this, Russia is among the countries with insufficient sunlight.
• Air pollution. Emissions from industrial enterprises, as well as smog and dust, prevent the penetration of ultraviolet rays.
• With age, there is a significant decrease in the skin's ability to synthesize vitamin D, which reaches 75% in people over 65 years of age.
• Skin tone. In people with darker skin, the level of vitamin D production is only one sixth compared to those with lighter skin. This is explained by the fact that melanin, which gives the skin its color, prevents the absorption of mid-range ultraviolet rays. Consequently, dark-skinned people require significantly more time in the sun for their bodies to produce the necessary amount of vitamin D.

Eventually, we begin to fear direct exposure to sunlight. Ultraviolet B radiation does not pass through glass, clothing, or even through a layer of sunscreen with a high SPF protection.

However, using sunscreen remains important, even in winter. In order to provide the body with the necessary amount of vitamin D, you will need to spend time in the sun until your skin becomes slightly red, which can be dangerous because it increases the risk of sunburn and, in the future, skin cancer.

Determining the optimal vitamin D option

There are seven compounds that have a similar chemical structure and for this reason are grouped under the general term "vitamin D". However, most often this name refers to two main varieties - D2 and D3. These forms of the vitamin differ in their provitamins, which are the original components, but they share a common property - inertness.

In order to be formed into fully active vitamin D (calcitriol), provitamins must undergo several additional transformations in the body [16], [13]. The pathway from provitamins to the active form of vitamin D can be described as follows:

• From plant sources, the provitamin ergosterol is converted into vitamin D2, known as ergocalciferol. This vitamin then enters the liver, and then the kidneys, where it is converted into the active form of vitamin D.
• Sunlight and animal products contribute to the formation of provitamin 7-dehydrocholesterol, which is converted into vitamin D3, known as cholecalciferol. This process then continues in the liver, and then in the kidneys, where the active form of vitamin D is formed.

Vitamin D2 is converted into the active form more slowly than vitamin D3, which is why the third form is more often found in vitamin supplements [15]. However, after both forms are converted in the body, their effects on metabolism are the same.

Optimal daily intake of vitamin D.

Rospotrebnadzor specifies the following standards [17]:

• For adults, the daily intake is 15 micrograms, which is equivalent to 600 international units.
• For people over 65 years of age, the recommended daily dose is 20 micrograms, which is equivalent to 800 international units.
• The recommended daily dose for children is 10 to 15 mcg, which is equivalent to 400–600 international units.

Why is the dosage of vitamin D indicated in international units (IU)? At the beginning of its use, this vitamin was used primarily for the treatment of rickets, and therefore the emphasis was not on the quantity of the substance, but on its biological activity, that is, the ability to prevent this disease. It is this activity that is usually measured in international units - IU [18].

One international unit (IU) corresponds to 0.025 mcg of vitamins D2 or D3. Therefore, 1 mcg of inactive forms D2 and D3 is equivalent to 40 international units of active vitamin D.

Sources of vitamin D: what foods contain it?

Let's clarify right away that vegetables and fruits do not contain this substance. However, in our list, you will find 11 products that contain vitamin D, including some plant-based options.

We will provide detailed information about each of the products presented.

The origins of fish oil as a food product date back to the Viking Age. Local residents of Scandinavia used cod liver extract, from which they made oil or fried the fish itself. It constituted a significant part of the diet of the peoples of Northern Europe.

Until 1970, fish oil was a mandatory element of the children's diet in the Soviet Union, as it was used to compensate for the lack of essential fatty acids and vitamins A and D. However, the concentration of vitamin D in fish oil was unstable, and the amount of vitamin A often exceeded the permissible norms, which could cause toxic reactions in the body. With technological advances, various pesticides and other harmful substances accumulated in cod liver began to leak into water bodies. Today, fish oil is produced from the muscle tissue of cod fish, which leads to a significantly reduced concentration of vitamin D in the finished product.

Cod liver is high in vitamin D, making it an excellent alternative to both fresh fish and less palatable canned fish oil. However, it's important to remember that this product is high in calories and fat, so frequent consumption is not recommended. Furthermore, caution should be exercised when choosing canned fish, as dangerous levels of arsenic have sometimes been found in cod liver.

Vitamin D content varies significantly between wild salmon and farmed fish. Salmon caught in North Atlantic waters has the highest levels of this vitamin, while the amount of vitamin D in farmed fish depends on its diet. For example, if salmon is fed microalgae, it can accumulate more valuable nutrients.

The Union of Pediatricians of Russia reports the following information about the vitamin D content of salmon [15]:

Don't miss the opportunity to pay attention to a can of sardines, as they can satisfy up to 50% of the daily requirement for vitamin D and have a positive effect on brain function. Researchers from the University of Greifswald in Germany analyzed the relationship between vitamin D levels and the aging process of the brain. After examining magnetic resonance imaging (MRI) data from 1,865 participants, they concluded that vitamin D deficiency may contribute to accelerated brain aging.

Canned tuna does not have the same nutritional value as Inferior to farmed salmon. One package of tuna contains a third of the daily requirement of vitamin D.

Summer eggs can contain twice as much vitamin D as winter eggs, as confirmed by a study by scientists from the Institute of Agricultural and Food Sciences in Germany. To increase vitamin D levels in eggs, birds have been released outdoors, where they can be exposed to sunlight. As a result, the concentration of this vitamin in dry matter has increased by 3 μg, which corresponds to 120 international units per 100 grams of product.

Mushrooms such as shiitake, button mushrooms, and oyster mushrooms contain the plant provitamin ergosterol. When exposed to direct sunlight, this provitamin is transformed into vitamin D2. When cultivating mushrooms, ultraviolet irradiation is often used to initiate this conversion process. The amount of vitamin D2 that accumulates in mushrooms depends on the duration of irradiation and the various conditions in which they are grown.

In some countries, the vitamin D level in milk is 400 IU per liter, which corresponds to approximately 75% of the required daily dose [15]. To achieve this fortification of milk, cows are exposed to artificial ultraviolet radiation for several hours.

Employees of the United States Department of Agriculture (USDA) conducted calculations to find out how much vitamin D is contained in one cup (230 ml) of both whole and plant-based milk.

According to information provided by the USDA, natural yogurt made from whole cow's milk contains 31 international units of vitamin D. At the same time, in yogurts with additives, this figure can reach 200 international units. Belgian experts conducted an interesting study [25], which found that daily consumption of one 125-gram yogurt fortified with calcium (400 mg) and vitamin D (200 IU) can reduce the risk of fractures caused by bone loss. This effect is especially noticeable in people over 70 years of age.

In 2012, the European Commission, responsible for dietetic products, nutrition and allergies (EFSA), gave permission for the use of ultraviolet-irradiated yeast as a new food component. This yeast is used in the production of bread and various flour confectionery products. 100 grams of this product contain 200 international units of vitamin D2.

Cocoa beans, which serve as the basis for chocolate production, contain a certain amount of fungi. These microorganisms are able to accumulate ergosterol, which is a precursor of vitamin D2.

Julia Kühn, a scientist at the Institute of Agricultural and Food Sciences in Germany, and her team believe that solar drying Cocoa beans promote the conversion of ergosterol to vitamin D2. As a result, the vitamin D content in dark chocolate can vary from 1.90 to 5.48 μg, which corresponds to 76–216 international units per 100 grams of product.

Is it possible to meet the need for vitamin D through diet alone?

Even the most carefully balanced diet typically contains a deficiency of at least 20% of the daily vitamin requirement. To compensate for this deficiency, a person would have to double the amount of food consumed. In addition, for full absorption of vitamin D in the intestine, the diet must contain fat, since this vitamin is fat-soluble. However, increased fat consumption can lead to excess weight gain. Thus, if you have a vitamin deficiency, you should not rely solely on foods rich in vitamin D, and experts advise considering the use of vitamin supplements.

Differences between vitamin D supplements and vitamin complexes

According to the standards of GOST R 57106-2023, vitamin and mineral complexes are divided into two categories [27]:

• In the first option, the vitamin content is insignificant, not reaching the recommended daily intake.
• In the second option, there may be both the daily intake and an amount significantly exceeding it.

There are also medications for vitamin therapy that contain vitamins in an amount that can many times exceed the recommended daily intake.

Thus, in order to determine the deficiency and select the appropriate medication, you should consult with doctor.

Sources

Semin S. G., Volkova L. V., Moiseev A. B. and Nikitina N. V. in 2012 published an article on the possibilities of studying the biological function of vitamin D in the journal "Pediatrics" named after G. N. Speransky, in issue 91, number 2, pages 122 to 131.

Dolgikh Yu. A., Verbovaya N. I. Vitamin D in various manifestations // Pharmateka. 2020. 4. 12–21. DOI: 10.18565/pharmateca.2020.4.12-21.

Khosravi Z. S., Kafeshani M., Tavasoli P., Zadeh A. H., and Entezari M. H. conducted a clinical study on the effect of vitamin D supplementation on weight loss, glycemic control, and lipid profile in overweight and obese women. The results of the study were published in the International Journal of Preventive Medicine in 2018, issue 9, article 63. DOI: 10.4103/ijpvm.IJPVM_329_15.

Xie F., Huang T., Lou D., Fu R., Ni C., Hong J., Ruan L. An updated meta-study analyzing the effect of vitamin D supplementation on the incidence and outcomes of depression based on randomized controlled trials was conducted // Frontiers in Public Health. 2022. 10. 903547. DOI: 10.3389/fpubh.2022.903547.

Botelho J., Machado V., Proença L., Delgado A. S., Mendes J. J. "Vitamin D deficiency and oral health: an extensive review." // Nutrients. 2020. Vol. 12, No. 5. Article. 1471. DOI: 10.3390/nu12051471.

Hoe E., Nathanielsz J., Toh Z. Q., Spry L., Marimla R., Balloch A., Mulholland K., Licciardi P. V. (2016). The effect of vitamin D on inflammatory processes in human immune system cells under conditions of bacterial infection // Nutrients. 2016. 8(12). 806. DOI: 10.3390/nu8120806.

Egshatyan L. V. Vitamin D: non-classical effects. Obesity and Metabolism. 2018. 15(1). 12–18. DOI: 10.14341/omet2018112-18.

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Kodentsova V. M., Sarkisyan V. A., Vorobyova V. M., Vorobyova I. S., Kochetkova A. A., Risnik D. V. Study of food fortification with vitamin D: world experience and modern directions // Food industry. 2019. (9). 70–74. DOI: 10.24411/0235-2486-2019-10146.

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Gozdzik A., Barta J. L., Wu H., Wagner D., Cole D. E., Vieth R., Whiting S., Parra E. J. conducted a study in which vitamin D levels were examined during the winter period in healthy young adults with different backgrounds living in the Toronto area. The study revealed a relationship between vitamin D levels and intake of this vitamin, as well as skin pigmentation. The results of the work were published in the journal BMC Public Health in 2008, volume 8, article 336. DOI: 10.1186/1471-2458-8-336.

Khabarov S. V., Khadartseva K. A., Volkov V. G. Vitamin D issues and its impact on women’s reproductive health // Russian Bulletin of Obstetrician-Gynecologist. 2020. 20(5). 45–53. DOI: 10.17116/rosakush20202005145.

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Kodentsova V. M., Mendel O. I., Khotimchenko S. A., Baturin A. K., Nikityuk D. B., Tutelyan V. A. study the physiological requirements and optimal dosages of vitamin D necessary to eliminate its deficiency. This article considers the current state of the problem. The publication was published in the journal «Nutrition Issues» in 2017, issue 86(2), pages 47–62. DOI: 10.24411/0042-8833-2017-00033.

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Mueller, J., Pauly, M., Molkentin, J., Ostermeyer, U., van Muilekom, D. R., Rebl, A., Goldammer, T., Lindemeyer, J., Schultheiß, T., Seibel, H., and Schulz, C. (2023). Use of microalgae as functional feed for Atlantic salmon: Effects on growth, health, immunity, muscle fatty acid content, and pigment accumulation. Frontiers in Marine Science. 2023. 10. 1273614. DOI: 10.3389/fmars.2023.1273614.

Krolevets A. A., Myachikova N. I., Binkovskaya O. V., Glotova S. G. et al. (2021) presented a study on the use of a nanostructured vitamin to fortify food products. The article was published in the journal "Food Product Specialist" in 2021, issue 3, pages 166–173. DOI: 10.33920/igt-01-2103-01.

Kühn J., Schutkowski A., Kluge H., Hirche F., Stangl G. I. Raising free-range chickens: a natural way to produce vitamin D-rich eggs // Nutrition (Burbank, Los Angeles County, CA). 2014. 30(4). 481–484. DOI: 10.1016/j.nut.2013.10.002.

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Ethgen O., Hiligsmann M., Burlet N., Reginster J. Y. conducted a study on the cost-effectiveness of individualized intake of dairy products fortified with vitamin D in the fight against osteoporotic fractures. The results of their work were published in the journal Osteoporosis International, which is a collaboration between the European Osteoporosis Foundation and the National Osteoporosis Foundation of the USA, in 2016. The article was published in Volume 27, Issue 1, on pages 301–308. DOI: 10.1007/s00198-015-3319-3.

Kühn J., Schröter A., ​​Hartmann B. M., Stangl G. I. Chocolate and cocoa contain vitamin D2. Food Chemistry. 2018. 269. 318–320. DOI: 10.1016/j.foodchem.2018.06.098.

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