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What does vitamin D do?
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Vitamin D For Dummies
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However, natural diets typically do not contain adequate quantities of vitamin D, and exposure to sunlight or consumption of foodstuffs purposefully supplemented with vitamin D are necessary to prevent deficiencies. Vitamin D, as either D 3 or D 2 , does not have significant biological activity. Rather, it must be metabolized within the body to the hormonally-active form known as 1,dihydroxycholecalciferol. This transformation occurs in two steps, as depicted in the diagram to the right:.
Vitamin D recommendations for infants: information for health professionals
Each of the forms of vitamin D is hydrophobic, and is transported in blood bound to carrier proteins. The major carrier is called, appropriately, vitamin D-binding protein. The halflife of hydroxycholecalciferol is several weeks, while that of 1,dihydroxycholecalciferol is only a few hours.
Hepatic synthesis of hydroxycholecalciferol is only loosely regulated, and blood levels of this molecule largely reflect the amount of amount of vitamin D produced in the skin or ingested. In contrast, the activity of 1-alpha-hydroxylase in the kidney is tightly regulated and serves as the major control point in production of the active hormone.
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The major inducer of 1-alpha-hydroxylase is parathyroid hormone ; it is also induced by low blood levels of phosphate. Interesting species differences exist in the ability to synthesize vitamin D through the sunlight-mediated pathway described above. The skin of humans, horses, pigs, rats, cattle and sheep contain adequate quantities of 7-dehydrocholesterol which can effectively be converted to cholecalciferol.
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In contrast, the skin of dogs and cats constains significantly lower quantities of 7-dehydrocholesterol than other species, and its photochemical conversion to cholecalciferol is quite inefficient; dogs and cats thus appear to rely on dietary intake of vitamin D more than do other animals. The active form of vitamin D binds to intracellular receptors that then function as transcription factors to modulate gene expression.
Like the receptors for other steroid hormones and thyroid hormones , the vitamin D receptor has hormone-binding and DNA-binding domains. The vitamin D receptor forms a complex with another intracellular receptor, the retinoid-X receptor, and that heterodimer is what binds to DNA.
www.gabrielgfx.com/wp-includes/come-posso/3973-cellulare-apple.php In most cases studied, the effect is to activate transcription, but situations are also known in which vitamin D suppresses transcription. The vitamin D receptor binds several forms of cholecalciferol. Its affinity for 1,dihydroxycholecalciferol is roughly times that for hydroxycholecalciferol, which explains their relative biological potencies. Vitamin D is well known as a hormone involved in mineral metabolism and bone growth.
You simply need to have the right dose usually in the form of a gel capsule , pop it into your mouth, and swallow it with a little water. No advantage is gained by taking a vitamin D supplement several times daily over taking one capsule once a day. A study at the Cleveland Clinic showed that if you take your vitamin D with the biggest meal each day, you can increase the level of vitamin D in the blood by an average of 50 percent.