Doctor's advice


Vitamin D is one of the most important vitamins, which we often talk about and mention during autumn and winter months, when its level in the body is lowest. Vitamin D plays an important role in the development of bones and teeth and in the functioning of the immune system. The human body can produce vitamin D from direct sunlight, which is why we call it "the sun vitamin". During short winter days our exposion to sunlight is not suffiecient to produce enough vitamin D.

Autumn days are getting shorter and shorter and nights longer, and it's usually already dark when we head home from work. We have more chance to enjoy the sun during weekends, but also then, the sun is not strong enough to get enough UVB rays for the body to create vitamin D. The general medical recommendation is to supplement our diet with vitamin D from October to April, when its deficiency is greatest.

What is vitamin D?

Vitamin D is a fat-soluble vitamin whose main function is to maintain a normal amount of calcium and phosphorus in the blood. The »sun vitamin«, as it is also called, plays an important role in bone building process during growth, takes care of the proper functioning of the muscles, supports the normal function of the immune system and contributes to cardiovascular health. It is the only vitamin that can be biosynthesized by the human body, that is in the skin, through sun exposure (specifically UVB radiation).

There are two forms of vitamin D:

  • vitamin D2 (ergocalciferol) can be found in foods of plant origin,
  • vitamin D3 (cholecalceferol) can be found in foods of animal origin, it is also formed with the help of sunlight (UVB rays).

Did you know?

Vitamin D is not actually a vitamin, as the name suggests, but a prohormone from which other important hormones are formed.

The vitamin D deficiency »pandemic«

Experts estimate that vitamin D deficiency is a major public health issue and a problem of pandemic proportions!

The amount of vitamin D that we produce during summer is only sufficient for a short period of time. Regular sun exposure has decreased due to changing lifestyles (staying indoors). Also, with the increasing recommendations of experts to use sunscreen to prevent skin cancer, the production of vitamin D was further reduced.

The problem of deficiency is not only problematic in the winter and autumn months but also in the summer. In our geographical zone, we mostly fail to make up for the lack of vitamin D we produce over the year if we don’t supplement it.

Infants and children are most exposed to the deficiency, while pregnant and breastfeeding women, elderly (over the age of 65), dark skinned and all those who stay mostly indoors are also considered to be at risk.

Vitamin D deficiency is considered a “silent deficiency,” meaning it has no obvious symptoms for quite long time.

The most common early symptoms are:

  • weight gain,
  • bone loss and fractures,
  • muscle cramps and weakness,
  • bone and joint pain,
  • weak immune system,
  • exhaustion and general fatigue,
  • blood sugar problems,
  • reduced calcium levels,
  • mood swings and irritability,
  • depression.

Vitamin D deficiency, however, can lead to bigger and more serious health issues:

  • rickets in children,
  • asthma,
  • diabetes,
  • periodontal diseases,
  • cardiovascular disease (high blood pressure and/or progressive heart failure),
  • fibromyalgia,
  • osteoporosis and/or osteopenia,
  • 17 different types of cancer (including breast, prostate and bowel cancer),
  • autoimmune diseases,
  • Parkinson's disease,
  • Alzheimer's disease,
  • chronic fatigue syndrome,
  • allergies,
  • skin diseases (dermatitis, eczema ...) ...

... And many other degenerative and autoimmune diseases.

Vitamin D and the immune system


Did you know?

Vitamin D increases the natural resistance (innate immunity) to infections.

One of the most important roles of vitamin D is to maintain a strong immune system, capable of successfully fighting viruses and bacteria that cause diseases, as it works directly with the cells responsible for fighting infections.

Scientists from the University of Copenhagen have discovered that Vitamin D is crucial to activating our immune defenses and that without sufficient intake of the vitamin, the killer cells of the immune system - T cells - will not be able to react to and fight off serious, life-threatening infections in the body.

Vitamin D could help us to combat infectious diseases and global epidemics. Research has shown that vitamin D deficiency affects the incidence of respiratory infections and flu. A 2010 Japanese study also showed that the incidence of influenza was reduced in schoolchildren who received vitamin D3 throughout the winter. The study finds that D3 supplements reduce the incidence of flu during the winter, especially in school children.

Vitamin D effectively protects the body against respiratory infections, as it stimulates the action of white blood cells, neutrophils and macrophages, which act as a protective barrier in the lungs.

Studies have also shown that vitamin D deficiency increases the predisposition to viral respiratory infections and that increased levels of vitamin D reduce this predisposition. One study reports that women who took 2,000 IU units of vitamin D daily for one year had virtually no symptoms of colds and flu.

How to ensure a sufficient supply of vitamin D?

Because the body partially biosynthesizes vitamin D, the nutritional needs for this vitamin are much harder to determine. They depend on the amount of biosynthesized (endogenous) vitamin D.

According to the latest recommendations, in the complete absence of biosynthesis, the human body needs 20 µg of vitamin D per day. Nutritional needs vary with the season and exposure to sunlight. In most European countries, there seems to be a shortfall in achieving current vitamin D recommendations, as the sunlight in autumn and winter is not sufficient to ensure an adequate production of endogenous vitamin D, so the adequate amount must be consumed with food.

The richest food sources of vitamin D are of animal origin; fish oil, fatty fish, egg yolk, liver, dairy products and foods fortified with vitamin D.


It is unfortunately a considerable challenge to receive enough vitamin D from food, as only a few food sources are rich in this vitamin. Let's see an example - to ensure the recommended daily intake of vitamin D, you should eat a large piece of salmon every day, which is practically impossible.

Therefore, it is recommended to supplement the diet with vitamin D, in the form of dietary supplements.

How much vitamin D do we actually need?

The European Food Safety Authority (EFSA) has set the upper intake level of vitamin D (from all sources; food, food supplements, fortified food) for children from birth to one year to 25 µg (1000IU), from 1 to 10 years to 50 µg (2000IU) and from 11 years onwards, including pregnant and breastfeeding women, to 100 µg (4000IU).

Globally, the lower limit of vitamin D in the blood is set  to 50 µg/l. Optimal levels should be between 50 and 80 µg/l.


Did you know?

Our body produces enough vitamin D if we expose our face, hands, décolleté or other parts of the skin to the sun light several times a week for about 15 minutes. It is important that we are directly exposed to sunlight and that we do not use sunscreen.


Author: Tina Kamenšak

Category: Doctor's advice

Published: 25.11.2020 08:48

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