Vitamin D is a fat-soluble vitamin. When there are large amounts in the body, it accumulates in the liver. Vitamin D differs from other nutrients in two ways.


First, it does not have to be obtained entirely from food, as the body can synthesize it under the influence of sunlight. When we do not get enough sunlight, we have to get it through food.


Second, some authors classify vitamin D as a hormone because it is produced in one part of the body and regulates processes in another.


Functions of vitamin D.

It is involved in regulating blood calcium levels, which is essential for bone health. Vitamin D regulates the absorption of calcium and phosphorus from the small intestine. When the body has a greater need, absorption is enhanced. Absorption decreases when needs are small. The vitamin also acts at the level of the kidneys by regulating the excretion of calcium in the urine.


How much vitamin D do we need?

With enough exposure to sunlight, you do not need to take extra vitamin D through your diet. But how can you be sure that sun exposure is enough?


Unlike calcium, vitamin D does not have a specific daily dose. Daily needs are determined by how much sunlight we get each day. There are many factors that affect the synthesis of the vitamin in the body - sunshine, latitude, season.


From the equatorial to the subtropical zone, the synthesis of vitamin D is ensured without any problems by the synthesis of the organism under the influence of sunlight. In temperate and polar latitudes, sunlight is not enough to cover the body's need for vitamin D in certain months of the year. The body will not be able to synthesize the required amount of vitamin during the winter season, as well as in early spring and late autumn.


In summer, when there is active sunshine, the body copes with the provision of vitamin D. 


Vitamin D is most intensively synthesized in strong sunlight - between 9 and 15 hours. On a cloudy day, its synthesis is very limited. People with darker skin have more melanin, which prevents the penetration of sunlight, which means the synthesis of vitamin D. In older people, the synthesis in the body is also difficult, which requires increasing the intake of the vitamin through food.


Foods, sources of vitamin D.

There are several forms of the vitamin, but only two are active in the body. These are vitamin D2, also called ergocalciferol and vitamin D3 - cholecalciferol. Vitamin D2 is found in many plant foods, while vitamin D3 is more commonly found in animal foods. This is the form in which the vitamin is synthesized in the body.


Most foods contain small amounts of vitamin D. And those foods that are a rich source of it - cod liver, mackerel - are not typical of the Western type of diet. That is why the so-called functional foods that are enriched with the necessary vitamins and minerals. Most often, vitamin D is added to milk.


Other foods that contain large amounts of vitamin D are cod liver oil, other oily fish such as salmon, mackerel, sardines, and also some grains that are fortified with the vitamin.


Eggs, butter, liver contain small amounts of vitamin D and in order to get the required dose of them a person must consume large amounts, which will not be healthy. Because plant-based foods contain very small amounts of the vitamin, vegetarians who do not consume dairy products need to get their daily dose of vitamin D from the sun or from vitamin-enriched foods such as soy, grains, or supplements.


What happens if we take more vitamin D than we need?

We can only overdose by taking supplements. Overdose causes hypercalcaemia (increased levels of calcium in the blood). The symptoms of this condition are: fatigue, loss of appetite, diarrhea, confusion, vomiting, excessive urine production, severe thirst.


Hypercalcemia is the cause of calcium deposits in the soft tissues - kidneys, liver and heart.


Vitamin D deficiency

Vitamin D deficiency in early childhood is associated with rickets. In Bulgaria, most pediatricians prescribe vitamin D as a dietary supplement for at least 1 year. This is the period of intensive growth in which the lack of the vitamin can affect the normal development of the child.


In later life, vitamin deficiency is associated with decreased bone density and diseases such as osteoporosis and osteomalacia. In adults over 55-60 years, especially in the winter season, it is also recommended to take vitamin D as a dietary supplement.