Vitamin D

- Functional effect : Required to be used for the absorption of calcium and phosphate/ Necessary for osteogenesis and maintenance.

- Helpful in reducing the risk of osteoporosis occurrence

What is vitamin D?

Fat soluble vitamin D has both characteristics of vitamin and hormone, as the nutrient necessary for use and absorption of calcium and phosphate. In addition, it is necessary for normal growth and development, and important especially for children’s development process of bones and teeth. 

The lack of vitamin D raises the incident rates of osteoporosis , bruise from a fall, and hip fracture as well as that of various cancer or autoimmune diseases and disorders. It also may lead to rickets for children and to osteomalacia for adults.

There are a few foods with high vitamin D content. The best sources of supply include oily fish such as salmon and tuna. Vitamin contained even in egg, butter and liver, but only a considerable amount of intake has effect, for which they are not that good as the sources of supply.

Known as “Sunshine vitamin” due to photosynthesis

Our body synthesizes vitamin D when it is directly exposed to sunshine. Exposure to sunshine two to three times a week on a clear day will be sufficient for biosynthesis of vitamin D.

In reality, however, decrease in outdoor activity due to busy schedule and increased use of sunscreen have led to the shortage of bio synthesized vitamin D. Especially in the Korean Peninsular located in north latitude 35~38°, the small amount of sunshine during winter (November~ March) is not sufficient for the synthesis of vitamin D. Therefore, it is recommended for the intake of vitamin D nutritional supplements which is little acquired from food or sunshine.

Types  of vitamin D; D2 (ergocalciferol) vs D3 (cholecalciferol)

There are several types of vitamin D, among which D2 (ergocalciferol) and D3 (cholecalciferol) are thought as main two categories. Vitamin D2 is created from yeast and vegetable sterol named ergosterol, while vitamin D3 can be synthesized by taking sunshine (ultraviolet ray) from 7-dehydrocholesterol which is the precursor of cholesterol. D2 exists in foods including mushroom or yeast, while vitamin D3 is contained in meat, fish, liver oil and dairy products. vitamin D3 has high bioavailability because it is the same in form to the vitamin D created in the body.

Metabolism of vitamin D

Vitamin D is stored in fat tissue and then delivered in protein connective form to liver through blood, when necessary. The OH bonding of Vitamin D is made in the location of carbon 25 in liver, transferred to 25(OH)D (25-hydroxcyvitamin D, Calcifediol), and then transferred in kidney to the final active type, 1,25(OH)2D (1,25-hydroxyvitamin D,calcitriol).

Vitamin D is stored in liver and whenever necessary, it is changed to medium activated form, 25(OH)D in blood. This medium activated form 25(OH)D passes through tissues whenever required, to be changed into complete activated form 1,25(OH)2D, activating as calcium homeostasis modulation and  cell growth, blood vessel creation, differentiation and face regulation.

The half life of medium activated form 25(OH)D is about 2 weeks. It is easy to specify and monitor the concentration in the body. Therefore, the vitamin D blood content is measured based on the concentration of medium activated form 25(OH)D.

Effect of vitamin D

1. Maintaining bone health

Bones repeat the process of generation and destruction to maintain its strength. For this, it is important to maintain proper level of blood calcium level. Vitamin D helps the absorption of calcium and phosphate in small intestine and maintains equilibrium, controlling the level of calcium and phosphate within the normal range, which is important in maintaining the strength of bones.

Vitamin D lowers in osteoporosis together with calcium, reducing the risk of fracture and bone density of the elderly.

2. Enhanced immunity

Vitamin D raises the immunity to help remove bacteria/virus of macrophage cells. And it reduces the rate of infection by enhancing the functions of white blood cells including natural killer cell (NK) and Tlymph cell/

3. Effective for healing and prevention of autoimmune diseases and disorders

Vitamin D has the two-sided immunity modulation effects, which increases the immunity but decreases it depending on cases, which prevents against excessive adaptive immunity and against autoimmune diseases and disorders such as rheumatic arthritis, atopy, and asthma. It was shown that people with the shortage of vitamin D had increased case of autoimmune diseases and disorders.

4. Cancer prevention

It is known that lower vitamin D blood content contributes the higher probability of breast cancer, colorectal cancer, prostate cancer, lung cancer and leukemia In addition, Its anti-cancer effect was found to inhibit not only cancer cells but also retrobulbar and new vessels developed to tumor.

5. Prevention of nerve cells

Brain and brain spinal fluid is widely distributed in the central nervous system, while vitamin D receptor in the peripheral nervous system. Vitamin D is known has protecting nerves, promoting the nerve cell division and proliferation, and removing toxIn nerve cells.

6. Control of high blood pressure

Vitamin D can help cardiovascular disease prevention and improvement through mechanism where Vitamin Dreceptor in endothelium cell inhibits excessive rise of blood pressure. It is reported the risk of high blood pressure declines by 8% whenever 10 higher of vitamin D blood content.

7. Inhibits the occurrence of diabetes

Many research results indicates that vitamin D can be helpful for diabetes, by inhibiting the production of cytokine that destructs beta cells of pancreas where insulin is produced, promoting the production of insulin and reducing the insulin resistance.

Related Articles

1. Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. (Institute of Medicine, Washington, DC: National Academy Press, 2010)

2. Rickets. (Whaton B, Bishop N, Lacet 2003:362:1389-400)

3. Occult vitamin D deficiency in postmenopausal US women with acute hip fracture. (LeBoff MS, et al., JAMA 1999;251:1505-11)

4. Vitamin D. (Holick MF, In: Shils ME, Shike M, Ross AC, Caballero B, Cousins RJ, eds. Modern Nutrition in Health and Disease, 10th ed. Philadelphia: Lippincott Williams& Wilkins, 2006)

5. Vitamin D effects in atopic dermatitis. (Samochocki Z,et al., J Am Acad Dermatol. ; 2013 Aug;69(2):238-44)

7. Vitamin D and cancer: current dilemmas and future research needs. (Davis CD, Am J Clin Nutr 2008:88:565S-9S)

8. Vitamin D3 supplementation in pations with frequent respiratory tract insfection: a randomized and double-blind intervention study. (Bergman P, et al., BMJ Open 2012 Dec 13;2(6). Pii e001663)