Vitamin D is a sterol that is considered to be a hormone since it is listed among the fat-soluble vitamins and can be synthesized endogenously at the same time.
Due to the low number of foods containing vitamin D, a small amount of this vitamin is taken with food. Fatty fish such as salmon, mackerel, tuna fish and sardines as well as egg yolk, milk, broccoli, green onion, parsley are rich in vitamin D. However, no food ingredient contains much vitamin D to meet the daily vitamin D requirement. The primary source of vitamin D synthesis is sunlight. For synthesis, direct sunlight contact on the skin is required. Factors such as latitude, seasons, sun’s angle of incidence to the earth, skin pigmentation, level of air pollution, sun protection creams applied on the skin and clothing types adversely affect this synthesis function.
Vitamin D applied to the skin or taken as a diet supplement is not biologically active. It is first converted to 25 hydroxyvitamin D [25(OH)D] in the liver, then to 1,25 dihydroxyvitamin D[1,25(OH)2D], which is a biologically active form in the kidneys.
1,25 dihydroxyvitamin D controls approximately 200 genes by forming a complex with the vitamin D receptor in 37 different tissue cells such as pituitary gland, ovaries, skin, stomach, pancreas, thymus, breast, kidney, parathyroid glands and peripheral leukocytes.
Its most important effect is on calcium, phosphorus metabolism and bone mineralization. However, in the recent years, it has been found that deficiency and insufficiency of Vitamin D is associated with many chronic diseases, including common cancers, cardiovascular diseases, metabolic syndrome, infectious and autoimmune diseases.
To assess the vitamin D levels in the person, 25 hydroxyvitamin D [25(OH)D] level should be considered showing both vitamin D intake and endogenous production. If the level of 25(OH)D is below 20 ng/ml, then vitamin D is considered to be deficient and if the level is 21 and 29 ng/ml, vitamin D is considered to be insufficient and if the level is higher than 30 ng/mL, then Vitamin D is considered to be at a sufficient level (the preferred level range is between 40-60 ng/ml) whereas if it is higher than 150 ng/ml, this situation is accepted as Vitamin D intoxication.
Sufficient level of Vitamin D intake and preservation of the optimum level of vitamin D in serum are not only important for bone, calcium and phosphorus metabolism, but also for general health status.
Vitamin D deficiency is now considered a global epidemic. Vitamin D deficiency is observed to be widespread in the studies conducted both in our country and in the world. In particular, those who cannot benefit from sunlight efficiently, dark skinned people, old people, obese people, ones who take anticonvulsant and glucocorticoid medication are included in high risk group on vitamin D deficiency and insufficiency.
It has been reported that vitamin D has beneficial effects on the regulation of the immune system, autoimmune diseases, certain chronic diseases and on the prevention of cancer development.
Vitamin D deficiency in patients with diffuse musculoskeletal pain is observed to a common problem. The prevalence of vitamin D deficiency was found to be 73.9% in a study in which 14,925 patients over the age of 20 with extensive musculoskeletal pain have been evaluated.
A meta-analysis of 25 randomized controlled trials comprising 10,933 volunteers showed that vitamin D supplementation is effective in the protection against acute respiratory infections. While this effect was observed in daily or weekly use, it was not observed in the ones taking infrequent and high doses of supplements.
According to the meta-analysis results of 11 prospective studies in EPIC-Norfolk trial where 3,600 people were monitored, a decreasing correlation between serum 25(OH)D level and Type 2 DM frequency was observed and it was reported that Type2 DM risk was minimized with the intake of vitamin D supplements.
In the meta-analysis evaluation of 11 studies with 16,434 participants, it was reported that low serum (OH) D level was associated with a high risk of carotid atherosclerosis.
In the meta-analysis of 7 randomized controlled studies, it was reported that the frequency of asthma exacerbations was minimized with the intake of Vitamin D supplements.
2,000 IU Vitamin D supplement intake per day for 6 months significantly reduced the number of acute exacerbations in COPD patients.
Women with a serum (OH) Vitamin D level above 40 ng/ml are have a significantly lower risk of cancer than those with the level below 20 ng/ml.
Level of Vitamin D <30 ng/ml requires treatment. The target of the treatment is to keep the serum 25(OH) Vitamin D level at 30-50 ng/ml. At least 1,500-2,000 IU Vitamin D intake is required to maintain the serum 25(OH) Vitamin D level above 30 ng/ml in adults.
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