Vitamin D – properties, deficiency, sources

The human body is a very complex structure that requires nutrients to fuel it and provide it with the energy it needs to function efficiently. Many biological reactions occur thanks to the presence of specific compounds and vitamins that are essential for our body.

One such component is vitamin D, which is responsible for the proper functioning of many biochemical processes that enable tissues, and thus the body, to function properly. It is therefore worth learning how vitamin D affects the human body, how it is synthesised, what its sources are, and what other effects this complex component has.

1. Vitamin D – what is it and how is it produced by the body?
2. Vitamin D – types
3. Vitamin D – the best food sources
4. Vitamin D – its role in the body
5. Vitamin D supplementation – characteristics
6. What to combine vitamin D with?
7. Vitamin D – effects of deficiency and excess

Vitamin D – what is it and how is it produced by the body?

Vitamin D is one of the most important compounds in our body. It is difficult to determine what this vitamin is not responsible for. The distribution of vitamin D receptors is so extensive that virtually all tissues in the human body have receptors for vitamin D, known as VDR. The biologically active form of vitamin D is calcitriol, which is synthesised in the kidneys through biochemical processes. A healthy vitamin D level is defined as between 75 nmol/l and 125 nmol/l, or between 30 ng/ml and 50 ng/ml.

How is vitamin D produced?

Vitamin D is synthesised by the human body thanks to the presence of UV rays, i.e. sunlight at the right frequency. The initial stage of the synthesis of this vitamin is the formation of cholecalciferol. In order for this form of the vitamin to be produced, sunlight is necessary to convert 7-dehydrocholesterol into cholecalciferol. The incomplete form of the vitamin then undergoes further enzymatic processes in the liver, to which it is transported by a vitamin D transport protein. There, our provitamin undergoes one more enzymatic conversion and is transported further to the kidneys, where the final product, calcitriol, which is the biologically active form of vitamin D, is synthesised.

A similar metabolic process occurs when consuming foods rich in vitamin D or supplements containing it. Both sources of vitamin D2 and D3 pass through the digestive tract, where they are further absorbed by appropriate transport proteins to the liver and then to the kidneys for biochemical conversion.

Vitamin D – types

There are two basic types of vitamin D. In nature, there is an animal form, cholecalciferol, and a plant form, ergocalciferol. Of course, it is also worth remembering the forms of provitamin D found in skin tissue, namely the aforementioned 7-dehydrocholesterol.

Vitamin D3

Cholecalciferol, the animal form of vitamin D, is more easily absorbed and efficiently converted into calcitriol. It can be synthesised in the skin in the presence of sunlight and supplied with food.

Vitamin D2

Ergocalciferol is a plant form of vitamin D with a shorter half-life. It undergoes very similar metabolic processes to cholecalciferol. Ergocalciferol is found mainly in mushrooms and a small group of plants that can produce this form of vitamin D when exposed to sunlight.

Vitamin D – the best food sources

Vitamin D, as we know, is a very important component for health. Its synthesis in the body is efficient and effective when the skin is exposed to UV rays, but we cannot always count on the presence of sunlight. This is where dietary sources of vitamin D come in handy. Vitamin D can be found in both animal and plant products.

Animal sources of vitamin D

The richest animal sources of vitamin D include:

• cod liver oil
• fish
• meat
• dairy products and their derivatives
• eggs
• fortified products
• supplements

Undoubtedly, one of the most well-known sources of vitamin D is fish, but its consumption is not frequent enough in Poland to efficiently meet the daily requirement for vitamin D, especially outside the summer season. In this case, it is worth supplementing its deficiency with other foods, which will minimise the effects of this vitamin deficiency. Another excellent solution is long-term supplementation with vitamin D in a dose tailored to the individual.

Plant sources of vitamin D

Plant sources of vitamin D should not be forgotten either. Although vitamin D2 (ergocalciferol) is not as common in plant products as it is in animal sources, it is worth knowing which products also contain this form of the vitamin. Plant sources of vitamin D include:

• mushrooms (including champignons, porcini and chanterelles)
• yeast

When taking preventive measures, it is worth diversifying your diet as much as possible, taking into account many potential sources of vitamin D. It will definitely be more difficult for people on a vegan diet to supplement vitamin D, but there are dedicated preparations for this group of people.

Vitamin D – its role in the body

As mentioned earlier, vitamin D is responsible for regulating many functions in the human body. It is therefore important to maintain its proper concentration, which will allow you to stay healthy in the long term, while of course maintaining good health habits.

Vitamin D and the immune system

The first very important system affected by vitamin D is the immune system. It is the first line of defence against pathogens and other environmental factors. The correct concentration of vitamin D effectively protects the body against upper respiratory tract infections. This is important both for physically active people and those who undertake the hardships of professional and family responsibilities.

In addition, vitamin D helps to increase the activity of lymphocytes, macrophages and NK cells, which allows for the efficient and effective removal of pathogens from our body.

Other uses of the vitamin in the course of other diseases related to infections and contagions are currently being researched, but we will have to wait for the results of such work. Certainly, the right concentration of vitamin D allows the body to remain highly alert to all kinds of bacteria and viruses, which helps to maintain high performance.

Vitamin D and the skeletal system

Another important system that benefits from adequate vitamin D levels is the skeletal system. This is actually one of the best-known properties of vitamin D. Optimal calcium and phosphate metabolism is key to maintaining a healthy musculoskeletal system. Many activities undertaken by the human body require effort, which causes inflammation in the skeletal system and beyond. Some inflammatory diseases, such as hyperthyroidism, can have a similar effect.

Vitamin D deficiency results in a dangerous loss of bone mass, which leads to osteoporosis and osteomalacia, i.e. a decrease in bone density. These conditions increase the risk of fractures and injuries during physical activity.

Vitamin D increases the absorption of calcium and its deposition in the bones and contributes to an increase in bone mass in the musculoskeletal system. It is a very important element of prevention, which, unfortunately, is increasingly neglected, for example due to information about the harmful effects of consuming large amounts of dairy products. In summary, in order to maintain the homeostasis of the skeletal system, it is important to ensure adequate levels of vitamin D, which regulates calcium and phosphate metabolism. It is also important to consume lean and sugar-free dairy products, which are a valuable source of calcium and vitamin D, on a regular but moderate basis. If you are deficient in this vitamin, you should consider taking an appropriate dose of supplements.

Vitamin D and the nervous system

Another important part of the body where vitamin D plays a significant role is the nervous system. Thanks to its proper functioning, the human body is able to take on various psychophysical challenges in an effective and sustainable manner. Unfortunately, the current times are not conducive to good nervous tissue condition. Frequent problems with sleep, regeneration and unhealthy lifestyle choices impair the efficiency of the nervous system, which adversely affects cognitive functions such as concentration, association of facts, coordination, etc. Vitamin D deficiency is often a common cause of these problems.

The numerous distribution of vitamin D receptors in brain tissue, i.e. in the main command centre of the nervous system, indicates the important role of this vitamin in the proper functioning of nerve tissue. The correct concentration of vitamin D protects the cells of the nervous system, regulates the secretion of neurotransmitters, which affects the body's biological clock, allows the creation of new brain connections through the formation of new neurons, has an anti-inflammatory effect and reduces the risk of developing neurodegenerative diseases.

As demonstrated in numerous scientific studies, vitamin D deficiency increases the risk of inflammation in the nervous system, such as Alzheimer's disease, Parkinson's disease, or problems with dementia and multiple sclerosis. It has also been shown that vitamin D deficiency contributes to depression.

As can be seen, vitamin D is undoubtedly a key component influencing the health of the body and nervous system. In addition to vitamin D, other dietary components, such as Omega-3 fatty acids, also play a similar role. It is therefore important to ensure a varied diet and regular vitamin D supplementation in order to maintain the health of the nervous system and reduce the risk of psychophysical problems as much as possible.

Vitamin D and the muscular system

Another equally important system in the human body is the muscular system. The changing lifestyle of many people who want to take pro-health measures means that we are seeing an increasing desire to engage in physical activity. This is a very promising trend, but it is important to remember that simply practising various types of exercise may not be enough. It is also necessary to ensure that the muscular system is resistant to all kinds of stress stimuli.

In the case of physical activity, the right concentration of vitamin D improves muscle contraction and muscle strength, which proves to be a key element in the continuous improvement of exercise performance and technique. In addition, our vitamin regulates testosterone levels and improves regeneration, which in the long term enables the human body to cope with regular exercise with similar or even higher efficiency.

Vitamin D and activity-related injuries

An important aspect of vitamin D, or rather its adequate concentration, is its support for the regeneration process after muscle and tendon injuries. This is not new (injuries) among people who train regularly, but it is worth keeping this property of vitamin D in mind when undertaking regular exercise, not only by professionals or semi-professionals, but also by amateurs. This can be useful in terms of the time needed to achieve full recovery.

Vitamin D and the digestive system and irritable bowel syndrome (IBS)

Vitamin D also improves the regulation of the digestive tract and regulates carbohydrate metabolism. It has been shown that vitamin D deficiency contributes to the development of irritable bowel syndrome, or rather to the symptoms of this disorder. Unfortunately, digestive system disorders are quite common, and vitamin D deficiency is one of the main causes of these problems. It is therefore important to ensure an adequate intake of vitamin D through food and supplementation in order to keep the digestive tract in good condition. This will help regulate bowel movements, resulting in a reduction in the severity of many unpleasant symptoms in people prone to heartburn, diarrhoea and constipation.

The preventive effect of vitamin D on carbohydrate metabolism consists in sensitising peripheral tissues to the action of insulin, which translates into better control of glycaemia, i.e. blood glucose levels. As a result, many other elements of hormone metabolism, such as testosterone, oestrogen and prolactin levels, remain at the right level, which has a positive effect on a person's well-being.

There are, of course, many other reports on the effects of vitamin D, e.g. in the context of liver, kidney, skin and other tissue function, but the systems mentioned above are those that require the most attention in terms of providing adequate amounts of vitamin D. In addition, they are characterised by the largest collection of medical data. It is therefore worth remembering that before taking any action related to higher than recommended supplementation with vitamin D or any other ingredient, you should discuss this possibility with a specialist, e.g. a doctor or dietitian.

Vitamin D supplementation – characteristics

An alternative source of vitamin D for the body is through appropriate supplementation. This should be supported by appropriate medical and dietary expertise, depending on the metabolic state, the presence of specific diseases and lifestyle.

Maintenance dose – how much vitamin D should be taken daily?

The preventive maintenance dose is currently set at 2000 IU/day. This dose may vary depending on anthropometric measurements such as height and body weight. In addition, the level of physical activity plays an important role. In view of the above, the preventive dose for people with a high body weight close to 100 kg may be 4000 IU/day. Other supplementation values should be discussed with a specialist.

What to combine vitamin D with?

In order to maximise the body's absorption of vitamin D, it should be taken after a meal containing fat. Examples of such meals include salad with olive oil, scrambled eggs, etc. Vitamin D is a fat-soluble compound, so it is necessary to include fat in the meal preceding supplementation.

There are also strategies that involve combining individual ingredients in supplements to maximise their mutual effects. Along with vitamin D, it is worth taking vitamin K2, which additionally supports the absorption of vitamin D and helps regulate calcium and phosphate metabolism. A similar supportive effect for vitamin D is noted with the participation of vitamin C, which also has an antioxidant effect, and vitamin B6, which helps in the synthesis of neurotransmitters for the nervous system and promotes better concentration. It also appears that the optimal combination is to use a complex supplement: vitamin D3 with vitamin K2 and fatty acids from the Omega-3 group.

Vitamin D – effects of deficiency and excess

To summarise the information gathered, it is also worth knowing what the symptoms of vitamin D deficiency are and what symptoms may characterise an excess of this vitamin.

Symptoms of vitamin D deficiency:

• difficulty falling asleep
• lack of concentration
• rapid fatigue
• chronic fatigue
• low physical performance
• immunity problems
• gastrointestinal problems (diarrhoea, constipation).

There are also rare cases of excessive vitamin D in the body. These are most often the result of unreasonable supplementation with excessively high doses.

Symptoms of vitamin D excess:

• nausea and vomiting
• headaches
• burning sensation on the skin
• excessive sweating and urination
• hyperactivity and periodic convulsions
• acute inflammation of the liver
• loss of appetite
• problems with gastrointestinal function
• general malaise, etc.

However, it is worth remembering that many scientific studies show that in our climate zone, where sunlight deficiency is common, the majority of the population has minor or major deficiencies of this vitamin. For this reason, it is worth considering regular supplementation with maintenance doses.

Sources:

• Witamina D – informacje ogólne (matabolizm, czym jest): https://phmd.pl/api/files/view/116222.pdf
• Rodzaje witaminy D: https://www.liposhell.pl/images/witaminy/4._Myszka_M_-_Immunomodulacyjne_dzia%C5%82anie_witaminy_D-skompresowany.pdf
• Źródła spożywcze witaminy D i suplementacja: http://www.wszechnica-zywieniowa.sggw.pl/Prezentacje/2015/slajdy_Witamina_D.pdf
• Właściwości witaminy D: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3349454/
• https://pubmed.ncbi.nlm.nih.gov/18689389/
• https://pubmed.ncbi.nlm.nih.gov/7015957/
• https://pubmed.ncbi.nlm.nih.gov/23320612/
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5900470/
• https://pubmed.ncbi.nlm.nih.gov/23336971/
• Objawy nadmiaru witaminy D: https://pubmed.ncbi.nlm.nih.gov/30294301/
• Objawy niedoboru witaminy D: https://www.ncbi.nlm.nih.gov/books/NBK532266/