Vitamin D (25 (OH) D) is a fat soluble vitamin like vitamins E, A and K and its key functions are related to the strengthening of calcium in the bones and teeth as well as the activation of various tissues in the body.
Vitamin D (25 (OH) D) has a chemical name as 1,25-dihydroxyvitamin D (1,25 (OH) 2D or calcitriol) that is associated with the thyroid gland in the synthesis of hormones involved with the homeostasis of calcium and phosphorus in the body.
Vitamin D is a steroid hormone that is well active in the form of calcitriol 25 (OH) 2D3 that is composed of A ring, B ring, Bicycle CD and side chains that can be replaced by other groups.
In 1650, Glisson, De Boot and Whistler found a bone disease with deformities of the limbs, large head and muscle weakness in the industrial cities of England and Northern Europe, which at that time was then referred to as rickets or English disease.
In 1822, Sniadecki noted that the cause of children with bone abnormality was likely to come from not receiving the sunlight.
In 1918, Mellanby experimented by feeding the dogs with foods with inadequate nutrition to make them suffer from the rickets and then providing them with vitamin A-rich foods leading to a better treatment. Therefore, he concluded that vitamin A could help to cure the bone disease.
In 1922, McColum provided vitamin A in foods other than cod liver oil and the results showed that such foods containing vitamin A could not treat the bone disease. Then, he experimented by eliminating vitamin A from cod liver oil with baking heat and the rest of cod liver oil was used to treat the bone disease in dogs. The results showed that the oil obtained could not cure such disease. He therefore concluded that there was likely a substance that is not vitamin A that positively affects the treatment of bone disease. He named this substance as “vitamin D”.
In 1935, the first vitamin D was extracted by Windaus who found more than 20 species of vitamin D.
Types of Vitamin D
1. Vitamin D2 or ergocalciferol or calciferor can be converted from ergosterol exposed to ultraviolet lightin the frequency range of 230 nanometers (nm), which is mostly found in plants and whole grains.
2. Vitamin D3 or cholecalciferol is mostly found in fish and in the cells of animals and humans from the conversion of 7 dehydrocholesterolin the skin after exposure to ultraviolet lightin the range of 275-300 nanometers(nm).
Functions and properties
• Vitamin D is important in regulating the secretion of parathyroid hormone that is associated with the balance of calcium and phosphorus in the body and facilitates the absorption of calcium and phosphorus in the gastrointestinal tract into the blood stream.
• Vitamin D stimulates the secretion of calcium from bone skins to bloodstream and plays a key rolein strengthening bones and accumulating calcium and phosphorus in bones.
• Vitamin D stimulates collagen synthesis and involves the use of carbohydrates.
• Vitamin D is essential to the functioning of the nervous system, promotes the functions of the musculoskeletal system, heartbeat and blood clotting that is associated with the balance and use of calcium and phosphorus in the body.
Effects of deficiency
1. Heart Failure
If the body is deficient in vitamin D, the amount of calcium in the bloodstream will decrease and the body is stimulated to release parathyroid hormone more. In addition, the function of thyroid gland excessively works that leads to the higher amount of calcium in the blood, which affects the control of blood pressure. This comes from two reasons as follows:
• Vitamin D deficiency is partly the cause of heart failure because the exchange of calcium in heart tissue membranes is abnormal and there is very little calcium as a result, the function and compression of the heart muscles are reduced.
• Vitamin D deficiency stimulates the renin-angiotensin system and the higher production of parathyroid hormone, which can cause higher blood pressure. In addition, there will be retention of water and minerals in heart tissues leading to the heart failure.
2. Deformity and osteoporosis
Vitamin D deficiency in childhood may result in abnormal body growth and abnormal and fragile bones. In addition, vitamin D deficiency in adults can cause osteopenia and osteoporosis as well as muscle weakness.
Sources of Vitamin D
Body can get vitamin D from two sources, including the synthesis of the body from the sunlight of about 80% and the foods of about 10-20%. We can control the level of vitamin D in the body in three ways, namely, exposure to sunlight through the skin, meals, and vitamin D supplements or pills.
• Synthesis of body
The skin in the granulosum level contains 7-dehydrocholesterol. When exposed to sunlight or ultraviolet B (UVB: 290 – 315 nm), this substance will be changed into previtamin D3 and vitamin D3, respectively. If there is too much vitamin D3 in the skin, it will be converted by UVB from sunlight into inactive photo products in order to maintain the balance of vitamin D3 in the body. Therefore, the sun can affect blood pressure indirectly due to the synthesis and balance of vitamin D from sunlight exposure, which affects the functioning of the parathyroid hormone.
Getting vitamin D from the outside is deemed a major source of vitamin D, which includes foods rich in various vitamin D species, such as salmons, mackerels, tunas, sardines, cod liver oil, eggs, mushrooms, milk, yogurts, and cereals. Meat foods often contain vitamin D3 (cholecalciferol) while plant foods usually contain vitamin D2 (ergocalciferol).
• Drugs and food supplements
Getting vitamin D from drugs should be in the right amount. If too much vitamin D is taken, it may cause a higher and toxic level of vitamin D due to excessive calcium absorption in the intestines. Vitamin D in the form of drugs and food supplements includes calcitriol 0.25 mcg/tablet, alfacalcidol (1-α-hydroxyvit D3), vitamin D2 (ergocalciferol) 20,000 IU/capsule and multivitamin (400 IU).
Vitamin D in body
When the body gets vitamin D from different sources, it will be converted to 25-hydroxyvitamin D in the liver and converted into the active form, namely, 1,25-dihydroxyvitamin D, at the kidneys.
Causes of deficiency
• Reduced synthesis of vitamin D by skin
– Absorption of ultraviolet B from sunlight decreases due to the use of sunscreen lotion. In addition, those with darker skin are likely to have less synthesis of vitamin D from the sunlight.
– Skin cells are declined due to senility when the amount of 7-dehydrocholesterol is reduced as well as to the skin grafts.
– Some diseases lead to a less absorption of minerals, such as diarrhea.
– Liver and chronic renal diseases contribute the body to produce in sufficient 25-hydroxyvitamin D.
– Obesity often creates the accumulation of vitamin D in fat so the less amount of vitamin D can be used.
• Use of some drugs
Some medicines inhibit the absorption of minerals, such as anticonvulsants, HIV treatment drugs and drugs that reduce fat absorption.
Eating certain foods without or with less vitamin D often increases the risk of vitamin D deficiency, such as carbohydrate-contained foods and breads.