The body can synthesize vitamin D through UVB rays that hit the skin when exposed to sunlight. This synthesis process occurs when the compound called 7-dehydrocholesterol in the skin is converted into vitamin D3 by UVB rays. Vitamin D is converted to a form called 25-hydroxyvitamin D in the liver. It then obtains its active form called 1,25-dihydroxyvitamin D in the kidneys. This active form is one that can interact with vitamin D receptors on many cells in the body.<\/p>\n
Vitamin D is a vitamin that participates in various biochemical processes in the body and has important functions. The main ones are:<\/p>\n
Calcium and Phosphorus Absorption<\/strong>: Active vitamin D increases the absorption of calcium and phosphorus in the intestines. In this way, calcium and phosphorus reserves are created for the body's use. Calcium and phosphorus play important roles in bone health, as well as in the nervous system and energy metabolism.<\/p>\n Bone Mineralization<\/strong>: Vitamin D supports bone health by regulating the mineralization process of bones. This involves the integration of calcium and phosphorus into bone tissue.<\/p>\n Immune system:<\/strong> Vitamin D can increase the body's defense against infections by regulating the activity of immune system cells. Active vitamin D may increase resistance to infections by increasing the production of compounds called antimicrobial peptides in body cells. Besides this, it can modulate the cellular immune response by regulating the activity of immune cells such as T lymphocytes. This helps the body create a more effective defense mechanism against harmful organisms. Vitamin D deficiency can cause a weakened immune system and decreased resistance to infections. Therefore, adequate intake of vitamin D is important to support the healthy functioning of the immune system.<\/p>\n Vitamin D not only increases the absorption of calcium obtained through food from the intestines, but also ensures the reabsorption of calcium that is about to be excreted from the kidneys, thus providing more calcium to be used in the body. Although this is a desired situation, there is a possibility that the extra calcium obtained will go to undesirable places. If vitamin D is combined with vitamin K2, vitamin K2 will activate the osteocalcin protein, allowing calcium to be integrated into the bone. In this way, consuming vitamins D3 and K2 together can increase bone density and prevent osteoporosis, especially in later ages.<\/p>\n Vitamin D Deficiency and Disease Risk<\/strong><\/p>\n D vitamini eksikli\u011fi, y\u00fcksek tansiyon, tip 2 diyabet (T2DM) ve obezite gibi risk fakt\u00f6rleri olan hastalarda \u00e7e\u015fitli kardiyovask\u00fcler sorunlarla birebir ili\u015fkilendirilmi\u015ftir (1,2). Bunun yan\u0131 s\u0131ra, 14 ng\/mL alt\u0131nda D vitamini seviyesi olan ki\u015filerin, D vitamini d\u00fczeyi 25 ng\/mL \u00fczerinde olan ki\u015filere oranla tip 2 diyabet g\u00f6r\u00fclme riskinin %43 daha y\u00fcksek oldu\u011fu g\u00f6zlemlenmi\u015ftir (3). Yap\u0131lan ba\u015fka bir \u00e7al\u0131\u015fmada, D vitamini eksikli\u011finin renin-angiotensin-aldosterone sistemi aktive etti\u011fi ve hem sol tarafl\u0131 kalp b\u00fcy\u00fcmesi, hem de hipertansiyona sebebiyet verdi\u011fi g\u00f6zlemlenmi\u015ftir (4).<\/p>\n Yak\u0131n tarihte, 2019 senesinde, yap\u0131lan bir meta analizin sonu\u00e7lar\u0131na g\u00f6re, 10 ng\/mL seviyesinden d\u00fc\u015f\u00fck D vitamini seviyelerinin Alzheimer riski ile pozitif bir korelasyona sahip oldu\u011fu g\u00f6sterilmi\u015ftir. Ayn\u0131 \u00e7al\u0131\u015fmada, bu ki\u015filere verilecek olan D vitamini takviyesi ile Alzheimer riski’nin %17 seviyesinde azalabilece\u011fi tespit edilmi\u015ftir (5). Bu olgunun olas\u0131 a\u00e7\u0131klamalar\u0131ndan biri, D vitamininin anti-enflamatuar etkisi sayesinde beyinde n\u00f6rodejeneratif hastal\u0131klar taraf\u0131ndan olu\u015fan inflamasyonu azaltmas\u0131d\u0131r. Yap\u0131lan \u00e7al\u0131\u015fmalarda, D vitamininin beyindeki perisit h\u00fccrelerinde transkripsiyon s\u00fcrecini etkileyerek antiinflamatuar \u00f6zelli\u011fe sahip oldu\u011fu tespit edilmi\u015ftir. K\u0131sacas\u0131, D vitamininin Alzheimer’da meydana gelen kronik inflamasyon durumunda beyin k\u0131lcal damarlar\u0131nda koruyucu etki g\u00f6sterdi\u011fi y\u00f6n\u00fcnde bulgular mevcuttur (6).<\/p>\n Yak\u0131n zamanda yap\u0131lan toplum temelli bir \u00e7al\u0131\u015fmada, orta derecede D vitamini eksikli\u011finin t\u00fcm demans grubu hastal\u0131klar\u0131 riskini %53 art\u0131rd\u0131\u011f\u0131n\u0131 g\u00f6stermektedir. \u015eiddetli eksiklik durumlar\u0131nda, yani 10 ng\/mL’nin alt\u0131ndaki seviyelerde, demans grubu hastal\u0131k riskinin %125 art\u0131\u015f g\u00f6sterdi\u011fi tespit edilmi\u015ftir. Genel olarak, 20 ng\/mL’nin \u00fczerindeki D vitamini d\u00fczeyi, optimum bili\u015fsel i\u015flevle en g\u00fc\u00e7l\u00fc korelasyonu g\u00f6sterir (7).<\/p>\n There are also findings in meta-analyses that vitamin D deficiency may also play a role in Parkinson's disease. There are studies showing that vitamin D levels below 30 ng\/mL may be associated with Parkinson's disease (8).<\/p>\n