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.

Vitamin D is a vitamin that participates in various biochemical processes in the body and has important functions. The main ones are:

Calcium and Phosphorus Absorption: 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.

Bone Mineralization: Vitamin D supports bone health by regulating the mineralization process of bones. This involves the integration of calcium and phosphorus into bone tissue.

Immune system: 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.

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.

Vitamin D Deficiency and Disease Risk

D vitamini eksikliği, yüksek tansiyon, tip 2 diyabet (T2DM) ve obezite gibi risk faktörleri olan hastalarda çeşitli kardiyovasküler sorunlarla birebir ilişkilendirilmiştir (1,2). Bunun yanı sıra, 14 ng/mL altında D vitamini seviyesi olan kişilerin, D vitamini düzeyi 25 ng/mL üzerinde olan kişilere oranla tip 2 diyabet görülme riskinin %43 daha yüksek olduğu gözlemlenmiştir (3). Yapılan başka bir çalışmada, D vitamini eksikliğinin renin-angiotensin-aldosterone sistemi aktive ettiği ve hem sol taraflı kalp büyümesi, hem de hipertansiyona sebebiyet verdiği gözlemlenmiştir (4).

Yakın tarihte, 2019 senesinde, yapılan bir meta analizin sonuçlarına göre, 10 ng/mL seviyesinden düşük D vitamini seviyelerinin Alzheimer riski ile pozitif bir korelasyona sahip olduğu gösterilmiştir. Aynı çalışmada, bu kişilere verilecek olan D vitamini takviyesi ile Alzheimer riski’nin %17 seviyesinde azalabileceği tespit edilmiştir (5). Bu olgunun olası açıklamalarından biri, D vitamininin anti-enflamatuar etkisi sayesinde beyinde nörodejeneratif hastalıklar tarafından oluşan inflamasyonu azaltmasıdır. Yapılan çalışmalarda, D vitamininin beyindeki perisit hücrelerinde transkripsiyon sürecini etkileyerek antiinflamatuar özelliğe sahip olduğu tespit edilmiştir. Kısacası, D vitamininin Alzheimer’da meydana gelen kronik inflamasyon durumunda beyin kılcal damarlarında koruyucu etki gösterdiği yönünde bulgular mevcuttur (6).

Yakın zamanda yapılan toplum temelli bir çalışmada, orta derecede D vitamini eksikliğinin tüm demans grubu hastalıkları riskini %53 artırdığını göstermektedir. Şiddetli eksiklik durumlarında, yani 10 ng/mL’nin altındaki seviyelerde, demans grubu hastalık riskinin %125 artış gösterdiği tespit edilmiştir. Genel olarak, 20 ng/mL’nin üzerindeki D vitamini düzeyi, optimum bilişsel işlevle en güçlü korelasyonu gösterir (7).

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).

I wish you healthy days,

Dr. Ahmet Ozyigit
Elite Research and Surgical Hospital

References:

1. Martins D., Wolf M., Pan D., Zadshir A., Tareen N., Thadhani R., et al. Prevalence of cardiovascular risk factors and the serum levels of 25-hydroxyvitamin D in the United States: data from the third national health and nutrition examination Survey. Arch Intern Med. 2007;167:1159–1165. doi: 10.1001/archinte.167.11.1159.

2. Paschou SA, Kosmopoulos M., Nikas IP, Spartalis M., Kassi E., Goulis DG, et al. The impact of obesity on the association between vitamin D deficiency and cardiovascular disease. Nutrients 2019;11 doi: 10.3390/nu11102458.

3. Mitri J., Muraru MD, Pittas AG Vitamin D and type 2 diabetes: a systematic review. Eur J Clin Nutr. 2011;65:1005–1015. doi: 10.1038/ejcn.2011.118.

4. Norman PE, Powell JT Vitamin D and cardiovascular disease. Circ Res. 2014;114:379–393. doi: 10.1161/CIRCRESAHA.113.301241.

5. Jayedi A., Rashidy-Pour A., Shab-Bidar S. Vitamin D status and risk of dementia and Alzheimer's disease: a meta-analysis of dose-response (†) Nutr. Neurosci. 2019;22:750–759.

6. Nissou MF, Guttin A., Zenga C., Berger F., Issartel JP, Wion D. Additional clues for a protective role of vitamin D in neurodegenerative diseases: 1,25-dihydroxyvitamin D3 triggers an anti-inflammatory response in brain pericytes J. Alzheimers Dis. 2014;42:789–799.

7. Littlejohns TJ, Henley WE, Lang IA, et al. Vitamin D and the risk of dementia and Alzheimer's disease. Neurology. 2014;83(10):920–928.

8. Zhou Z, Zhou R, Zhang Z, Li K. The Association between Vitamin D Status, Vitamin D Supplementation, Sunlight Exposure, and Parkinson's Disease: A Systematic Review and Meta-Analysis.