Vitamin D

Vitamin D or calciferols is a collective term for various substances (steroids), which in the true sense can be attributed to hormones. They can be formed by the human organism from cholesterol in the skin by solar radiation. The vitamin formed from cholesterol in the skin by sunlight is vitamin D3 or cholecalciferol. The plant-derived provitamin D, ergosterol is also converted by photolysis in the skin. It is called ergocalciferol or vitamin D2. Cholecalciferol and ergocalciferol have the same efficacy.

The overall occurrence in foods is very low. In most plant foods there is no preformed vitamin D. Mushrooms, spinach, some types of cabbage and yeast are an exception. There, ergocalciferol is present in relatively large amounts. In foods of animal origin, larger amounts of cholecalciferol are found only in fatty fish (salmon, trout, tuna, herring, etc.). Vitamin D is relatively heat-stable, which means that hardly any cooking losses of this vitamin are to be expected during the preparation (blanching or frying) of foods containing vitamin D. Vitamin D is very resistant to oxygen and light. It is very unstable to oxygen and light. Long storage times, especially in light, reduce the bioavailability of the vitamin.

Metabolism

Vitamin D is mainly stored in the liver. There and partly also in the kidney and in the intestine, vitamin D3 is further converted into a substance (D-hormone or calcitriol). This substance is responsible for the regulation of calcium metabolism.

Tasks

Vitamin D is a component of the endocrine system, where it is responsible for regulating calcium and phosphate metabolism. Vitamin D controls calcium resorption (absorption) from the intestine, when the blood calcium level drops.

Receptors for calcitriol (D hormone; a vitamin D metabolide) are located in many tissues, such as the gonads, heart, pancreas and thyroid. But what functions the hormone has there, or how it influences these tissues, is still largely unknown.

Occurrence

Vitamin D is formed by UV radiation (sunlight!) from precursors (e.g. 7-dehydrocholesterol, ergosterol), the so-called provitamins. Only a few foods contain vitamin D. It is found in cod liver oil and cod liver oil, herring and egg yolk. Particularly rich sources of vitamin D (μg/100g)

• Sardine 7,05
• Herring 31
• Salmon 16
• Cod 1,3
• Liver (poultry) 1.3
• Liver (beef) 1.7
• Veal 3.8
• Cod liver oil 330
• Cod liver oil 210 10th egg 3.5

Ergosterol is found in plants, while 7-dehydrocholesterol is found in animal tissues. Both compounds can, with sufficient UV light irradiation, be converted into biologically active substances, which we group together under the term vitamin D.

Health benefits of vitamin D

Vitamin D can prevent osteomalcia (bone softening) and promote bone health

Vitamin D maintains the balance of calcium and phosphorus in the body. More specifically, vitamin D promotes absorption of potassium and phosphorus in the digestive tract, calcium reuptake in the kidneys, and calcium mobilization in bone (1, 2, 3). Low vitamin D levels are associated with lower bone mineral density, inadequate bone mineralization, and increased risk of bone loss and fractures. Scientific research supports the role of vitamin D and calcium supplements in supporting bone health and reducing the risk for fractures (5, 6, 7, 8). Vitamin D deficiency can cause rickets in young children and osteomalcia (softening of bones) in adults. Both can be prevented by an adequate dietary intake of vitamin D (11, 12). For this, an attempt should be made to achieve vitamin D blood levels in the range of 20 to 50 mg/nl (4).

Vitamin D can protect against osteoporosis

Along with calcium supplements, vitamin D supplements may help protect older adults from osteoporosis (9). In addition to this, orally taken vitamin D may prevent osteoporosis from corticosteroid medications prescribed to relieve severe inflammation. Research suggests that vitamin D metabolites such as calcitriol and alfacalcidol are most effective for this purpose (10).

Vitamin D can support the function of the immune system

Studies have shown that vitamin D has potent effects on both innate and adaptive immunity. Vitamin D has the potential to positively influence a wide range of immune function imbalances, infections, and autoimmune diseases (13, 14).Cells such as macrophages, dendritic cells, T cells, and B cells involved in the immune response have receptors for vitamin D (15, 16).

Here is an overview of some of the effects of vitamin D on the immune system:

• Regulation of monocyte and macrophage activity (17, 18).
• Reduces the release of the proinflammatory cytokines IL-1, IL-2, IL-6, IL-8, IL-17, TNF-α, IFN-γ, and IL-12 (19, 20, 21).
• Increases the release of the anti-inflammatory cytokines IL-10 and IL-4 (22, 23).
• Inhibits the production of IgE by B cells and increases the production of IL-10 by dendritic cells and T cells, which plays an important role in allergic immune responses (24, 25)
• Reduces TFG-beta levels, which contributes to tissue repair (26, 27).
• Is crucial for the activation of T cells (28)
• Increases levels of CD8+ T cells, which is important for controlling viruses, bacteria, and cancer (29, 30)
• Increases the amount of natural killer T cells (31)
• Stimulates the release of antimicrobial compounds such as cathelicidin and beta-defensin 4 in response to infection (32, 33)

All these findings suggest that vitamin D helps maintain a healthy immune response. It reduces pro-inflammatory messengers and increases levels of anti-inflammatory compounds.

Vitamin D can protect against respiratory infections

Scientists have found that people who are vitamin D deficient are more likely to develop respiratory and pulmonary diseases, including tuberculosis. Limited research suggests that vitamin D supplementation may even prevent tuberculosis or reduce disease duration by strengthening the immune system (34, 35, 36). A number of studies have also shown that vitamin D supplementation-especially during the winter months-protects children from influenza and respiratory infections. As for adults, further research is needed on this (37, 38, 39). In addition to this, people who have HIV often suffer from vitamin D deficiency, which may further weaken their immune response. Some evidence suggests that supplementation may safely improve immune function and vitamin D status in these patients (40, 41, 42).

Vitamin D can alleviate inflammation and autoimmune diseases

Vitamin D helps reduce inflammation in the body. Studies have shown that it can balance immune function. Vitamin D has the potential to positively influence a wide range of immune problems, infections, and autoimmune diseases (43, 44). The potential of vitamin D to increase levels of regulatory T cells may be particularly important because regulatory T cells are immune cells that prevent the immune system from getting out of control. These cells can prevent allergic reactions as well as autoimmune tendencies (45).

To date, some studies suggest promising effects of vitamin D in the following inflammatory and/or autoimmune diseases:

• Multiple sclerosis (46, 47)
• Thyroid problems (48, 49)
• Lupus (50, 51)
• Rheumatoid arthritis (52)
• Irritable bowel syndrome (53, 54
• Chronic obstructive pulmonary disease (55, 56).
• Type 1 diabetes (57, 58)
• Asthma (59, 60)

All in all, studies have confirmed that vitamin D deficiency is more prevalent in people suffering from autoimmune diseases, inflammatory conditions, and allergic problems.

Vitamin D can help against low calcium levels in kidney disease

Oral vitamin D supplementation can effectively control low calcium levels and prevent complications such as renal osteodystrophy in people suffering from chronic renal failure and undergoing dialysis (61).

Vitamin D could help with psoriasis

Creams applied to the skin that contain specific forms of vitamin D (such as calcitriol and other analogs such as calcipotriene, maxacalcitol, and paricalcitolar) may help with psoriasis (62, 62).

Vitamin D could have a positive effect on dental health

Both vitamin D2 and vitamin D3 could reduce the risk of caries, with vitamin D3 likely to be more effective. Both have been compared with a placebo in babies, children, and teenagers in a clinical analysis (64). In the elderly, oral vitamin D3 supplementation appears to reduce the risk of tooth loss, according to one study (65).

Vitamin D could have a positive effect on heart health

Limited data suggest that vitamin D may reduce the risk of heart disease in some women. Early studies also highlight that cardiac patients have lower vitamin D levels (66).

Vitamin D could reduce the risk of cancer

Some studies have concluded that sufficiently high vitamin D levels may protect against some types of cancer and reduce the risk of death. Vitamin D may help prevent cancer by boosting the immune response, but the effects of vitamin D that protect against cancer are still under investigation (67). For example, some studies suggest that women who get more sun and eat more foods rich in vitamin D have a lower risk of developing breast cancer, while other studies have found no such association (68, 69, 70, 71). According to some studies, maintaining higher blood levels of vitamin D could also help prevent colorectal cancer. On the other hand, vitamin D deficiency could increase prostate cancer risk. However, further studies are needed before definitive conclusions can be drawn (72, 73).

Studies examining the effects of vitamin D on ovarian cancer have had mixed results. Thus, it is still unclear whether vitamin D can help prevent pancreatic cancer or ovarian cancer, although early studies suggest that it can (74, 75, 76). Normal vitamin D levels appear to be important for cancer prevention, but further studies are needed to investigate this association further.

Vitamin D could reduce the risk of type 2 diabetes

Studies show that supplementation with vitamin D has the potential to restore insulin secretion in specific cases (77, 78). However, the study results are mixed. There is evidence that vitamin D supplementation may be useful only in people who are at increased risk for diabetes and are vitamin D deficient. In a study conducted with women, an intake of 511 IU of vitamin D or more per day was associated with a lower type 2 diabetes risk (79). Vitamin D may play a role in delaying progression to type 2 diabetes in adults at increased risk for diabetes. In one study, vitamin D supplementation was associated with good pancreatic cell function. It also reduced an increase in HbA1C levels-a marker of blood glucose levels over several months-over time (80).

Vitamin D may have a positive effect on sleep and brain health and development

Normal vitamin D levels support emotional balance, cognitive function, and sleep quality (81, 82, 83). In addition to this, vitamin D is important for brain development, which is why pregnant women are recommended to consume at least 600 IU of vitamin D per day. Babies and children up to 12 months of age require 400 IU per day. In addition, vitamin D deficiency has been associated with a wide range of psychiatric and neurological disorders (84, 85). According to some researchers, low blood levels of vitamin D are associated with low mood, memory problems, and dementia (86, 87, 88). Some studies suggest that normal vitamin D levels may be protective against Parkinson's disease, although solid evidence for this is still lacking (89, 90).

Vitamin D could improve fitness

Clinical research suggests that vitamin D plays a role in muscle metabolism and function (91). Vitamin D could strengthen muscles and improve fitness. Vitamin D deficiency could make athletes more susceptible to injury, according to some studies (92, 93, 94). Studies also suggest that vitamin D may increase the physical strength of the limbs of the upper and lower body (95).

Vitamin D could help with obesity and metabolic problems

Vitamin D helps the pancreas produce insulin, which controls blood glucose levels. Deficiency could interfere with this process and is common in type 2 diabetics (96, 97, 98). Several studies have also found an association between low vitamin D levels and obesity. Studies suggest that higher blood levels of vitamin D may protect against obesity and the metabolic syndrome (99, 100, 101).

Vitamin D can support reproductive health

Vitamin D deficiency during pregnancy can harm both mother and child. It can lead to bone loss and osteomalacia (softening of bone) in the mother and impair growth, bone formation, and enamel formation in newborns (102, 103). Most experts consider vitamin D dosages of up to 4,000 IU safe during pregnancy. Vitamin D may also support fertility and reproductive health in men. Limited studies suggest that vitamin D may improve sperm motility, but these results are inconclusive at the present time (104, 105). Data on the effects of vitamin D on fertility in women are scarce. Limited research suggests that vitamin D may help women suffering from polycystic ovary syndrome, which affects ovulation and fertility. However, further, larger-scale studies are needed (106, 107).

Vitamin D can support skin and hair health

Vitamin D helps reduce inflammation in the body. Maintaining healthy vitamin D levels could help support skin and hair health. Some scientists believe that people with skin problems such as eczema, psoriasis, and hair loss should be monitored for vitamin D deficiency. However, more research is needed to support this practice (108).

According to limited research, vitamin D shows promise in the following:

• Eczema (109)
• Acne (110)
• Wound healing (111)
• Autoimmune hair loss (112)

Limitations

It is important to note that many studies conducted on the subject of vitamin D are correlational studies, meaning that a vitamin D deficiency correlates with a particular problem, but this does not mean that the deficiency is the cause of the problem. In numerous cases, the real reason for the health problems is that the affected individuals are not getting enough sun, rather than a vitamin D deficiency. Scientific research suggests that the sun has many health benefits that are independent of vitamin C. In this case, vitamin D deficiency is often a sign that the affected person is not getting enough sun, which could be the real cause of the problem.

Symptoms of deficiency

In the case of vitamin D deficiency, the absorption capacity of calcium is reduced. This in turn lowers the calcium concentration in the blood. This calcium deficiency has an unfavorable effect on bone structure in children and adolescents. The bones are insufficiently supplied with the stabilizing mineral, which leads to deformations of the skeleton (legs and spine) and to a lower load-bearing capacity of the bones. This corresponds to the clinical picture of rickets. The low blood calcium level can additionally lead to cramps and changes in nerve resilience. In adults, vitamin D deficiency can lead to decalcification of the skeleton and muscle nerve disorders. Decalcification of the skeleton is manifested by bone deformation and spontaneous fractures. Osteoporosis and even bone loss frequently occur.

Hypervitaminosis

Like vitamin A, vitamin D has very good storage properties and is only excreted in relatively small amounts. This quickly leads to damage to the organism when vitamin D is overdosed. Symptoms of hypervitaminosis D are:

• Nausea
• Vomiting
• Thirst
• Muscle weakness
• excessive excretion of calcium through the urine
• Increased urine volume

Demand

The vitamin D requirement or the supply recommendations are not as simple as with other vitamins. In principle, the body forms enough vitamin D to supply itself with sufficient sunlight. At the same time, the need for this vitamin varies due to many factors. Health, age, and the calcium and phosphorus content of the diet play a decisive role. The DEG (German Nutrition Society) recommends a daily intake of 0.005 mg with food for adults and children after the age of twelve months. For children under twelve months of age, expectant mothers and nursing mothers, the vitamin D requirement is slightly increased, which is why an additional intake of 0.01mg of vitamin D per day is recommended.

Demand in sport

Corticosteroids, e.g. cortisone and prednisone, which are not infrequently used in sports to treat injuries, deplete the body's own stores of vitamin D3. Long-term use of corticosteroids can thus lead to bone mass loss. My recommendation, take 200-400I.U. a day with a meal.

Interactions

Corticosteroids, e.g. cortisone and prednisone, which are not infrequently used in sports to treat injuries, deplete the body's own stores of vitamin D3. Long-term use of corticosteroids can thus lead to bone mass loss.

Supplement types of vitamin D

There are two forms of vitamin D: vitamin D2 and vitamin D3. Vitamin D2 (ergocalciferol) is primarily produced synthetically and added to foods.Vitamin D3 (cholecalciferol) is produced by the skin and is found in animal foods (113). Vitamin D3 is about 87% more effective than vitamin D2 in increasing and maintaining vitamin D levels in the body. This form is therefore preferable for supplements (114, 115).

Dosage

The official recommendation for vitamin D is as follows (116):

• Children up to 12 months: 400 IU per day
• Children, adolescents and adults up to 70 years: 600 IU per day(including pregnant and lactating women).
• People over 70 years: 800 IU per day

Since vitamin D is a fat-soluble vitamin, it is better absorbed when taken with fat. Bile salts help in the absorption of vitamin D in the digestive tract. Disorders of the digestive system, blocked flow of bile acid, and bile acid-binding drugs reduce vitamin D absorption (117, 118).

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