Vitamin D; The Physiology, Metabolism, and Deficiency

in StemSocial3 months ago

Vitamin B1 is Thiamine, vitamin B2 is Riboflavin, vitamin B3 Niacin (Nicotinic acid), vitamin B5 (Pantothenic), vitamin B6 is Pyridoxine, vitamin B7 is Biotin, vitamin B9 is Folate, vitamin 12 is Cobalamin and vitamin C is ascorbic acid - snippet from (vitamin C Physiology, Metabolism, and Deficiency)

In one of my previous posts, I discussed vitamin C Physiology, Metabolism, and Deficiency where I explained vitamin C, and its synthesis, and deficiency in the body. In today's post, I will be explaining vitamin D, its synthesis, and deficiency.

Vitamin D Absorption and Metabolism.

If you remember, in my previous post, I talked about water-soluble and fat-soluble vitamins, where we made mention that vitamin C was a water-soluble vitamin, well vitamin D is a fat soluble vitamin with multiple forms such as vitamin D2 (ergocalciferol), vitamin D3 (Cholecalciferol). Unlike water-soluble vitamin, fat-soluble vitamins dissolve in fat, and are stored in fat tissues in the body. Other fat-soluble vitamins are vitamin A, vitamin D, vitamin E, and vitamin K.

Vitamin D can be gotten from animal food products such as fish, meat, and milk, it can also be gotten from vitamin D supplements. But these aren't the only way to get vitamin D into the body. It can be gotten from Endogenous synthesis with the help of 7-Dehydrocholesterol in the epidermis of the skin, which converts UV lights such as light from the sun into vitamin D3 (Cholecalciferol). The recommended average daily intake would differ according to age, with adults (below 70 years) having 800 IU (International Unit), and 400 IU for children from age 12 months and above.

As usual, when vitamin D sources are ingested into the body, they go into the stomach through the esophagus. In the stomach, the Bile emulsify the fat, and the Lipase helps to break down the fat. It moves from the stomach to the Ileum, where it is absorbed into the bloodstream, then to the liver. It is acted upon by an enzyme in the liver called 25-hydroxylase which converts the vitamin D into 25-hydroxycholecalceferol and the excess vitamin D which isn't converted is stored in the liver. Furthermore, it is then transported to the kidney. In the proximal covoluted tubule, the parathyroid hormone triggers the enzyme 1-alpha-hydroxylase converts the 25-hydroxycholecalceferol to 1-25-dihydroxycholecalciferol. The Parathyroid hormones trigger the kidney to convert vitamin D, which increases in calcium binding protein in the small intestine, thereby increasing the calcium being absorbed into the bloodstream thereby increasing the amount of calcium level in the blood. This helps in bone health and a proper muscle and nervous tissue functioning.

Researches show that vitamin D boost the immune system by inducing antimicrobial peptides such as Cathelicidins, and Defendins, which binds to bacteria to reduce bacteria functioning, and virus (influenza) functioning. Also, a lot of people believe that vitamin D can inhibit the growth of cancer cells, well research are being done on that, and according to, the results for these researches have been inconsistent.

Vitamin D Deficiency and Treatment

Vitamin D deficiency can occur as a result of certain factors, such as Reduced Exposure to the rays of the sun (the amount of sunlight needed by the body differs with skin color, age, and time of being outside), Decrease Endogenous synthesis due to conditions such as Cirrhosis, Renal failure, HyperPTH, Not properly taking in vitamin D rich foods, and inability to absorb nutrients in the small intestine.

Patients with vitamin D deficiency would not show symptoms until it becomes a very serious case. Lack of vitamin D in the body could lead to Hypocalcemia in late findings, which usually affect the bone since lack of vitamin D causes inability of calcium to be absorbed from the gastrointestinal tract, into the bone. When there isn't calcium being absorbed into the bone, it becomes reabsorbed from the bone, which could cause bone pain, muscle twitching, myalgias, arthralgias, and fasciculations. Lack of vitamin D in the body could lead to conditions such as Osteomalacia (in adult), Osteoporosis, Rickets (in children), Osteopenia, and immunological dysregulation causing increase in incidence of tuberculosis, and influenza.

Vitamin D deficiency can be treated by taking vitamin D3 supplements to help increase the amount of vitamin D in the body. In cases where patients have hypocalcemia, introducing IV calcium into the body is necessary, while in patients that cannot metabolize fat, 1-25-dihydroxycholecalciferol (calcidiol) should be given.


The fact that vitamin D deficiency is very difficult to identify really calls for serious awareness into our health. Taking vitamin D supplements would help save us a lot of trouble than we can imagine.



Vitamin D can be ingested as you mention, but our body has the facility to form it, it is only necessary that we expose ourselves to the sun at least once a day.

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