Function Of Vitamin D In The Body – Vitamin D is unique among vitamins because we can synthesize most of what we need in our skin. Sunlight is an important ingredient in this process, so vitamin D is sometimes called the “sunshine vitamin.” However, the amount of vitamin D synthesized in the body is usually not enough to meet our needs, so most people need to eat food sources.
The formation of vitamin D in the skin begins with the conversion of cholesterol to 7-dehydrocholesterol. Then, in the presence of ultraviolet (UV) rays from the sun, 7-dehydrocholesterol is converted into vitamin D.
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Function Of Vitamin D In The Body
Both are inactive until they undergo two hydroxylations—a chemical reaction that adds a hydroxyl (-OH) group. The first hydroxylation occurs in the liver, creating calcidiol. This is the circulating form of vitamin D and the form that is measured in the blood to assess the human status of vitamin D. The second hydroxylation occurs in the kidneys and forms calcitriol, the biologically active form of vitamin D.
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Remember in our discussion of blood calcium regulation that one of the actions of parathyroid hormone (PTH) is to stimulate kidney enzymes that do this last step in the use of vitamin D. Active vitamin D increases the absorption of both calcium and phosphorus. in the intestines, and working with PTH to reduce the loss of calcium in the urine and promote the release of calcium and phosphorus from the bone. In these ways, vitamin D plays an important role in both maintaining blood calcium homeostasis and improving the supply of calcium and phosphorus in bone formation. Vitamin D deficiency causes poor bone health, which has serious consequences for children and adults, as we will discuss later on this page.
It is converted by a reaction that occurs first in the liver (making calcidiol) and then in the kidneys (making calcitriol, the active form). Once active, vitamin D works in several ways to ensure calcium homeostasis of the blood and improve the availability of calcium for bone formation.
Besides its role in bone health, vitamin D has many other functions in the body. Cells throughout the body have vitamin D receptors in their nuclei, and by binding to these receptors, vitamin D is thought to regulate the expression of hundreds of genes. Specifically, vitamin D is known to play an important role in regulating cell division and growth, immunity, insulin production, and blood pressure. Research has found
Between low circulating vitamin D levels and increased risks of chronic diseases, including cancer, diabetes, cardiovascular disease, and multiple sclerosis. However, it has been difficult to determine whether vitamin D deficiency actually contributes
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For most people, vitamin D synthesis in the skin provides an important part of their body’s needs, and a little sun exposure can go a long way. Vitamin D researchers suggest that most people need between 5 and 30 minutes of sun exposure between 10 AM and 3 PM, at least twice a week, to synthesize enough vitamin D. However, anything that reduces exposure to UV rays can interfere with Vitamin D synthesis, including the following:
Due to many factors affecting exposure to UV rays, most people are unable to absorb enough vitamin D for at least half of the year. Because vitamin D is fat-soluble, the liver and adipose storage can provide the body for some time. Additionally, food sources and supplements may be needed to meet vitamin D requirements.
Only a few foods are naturally good sources of vitamin D. These include fatty fish such as salmon, tuna, and mackerel, as well as fish liver oils (eg, cod oil). Small amounts are found in egg yolks, cheese, and beef liver. Additionally, some mushrooms grown in UV light can be a good source of vitamin D.
Most cow’s milk is fortified with vitamin D in the U.S. and Canada, but other dairy products such as ice cream and cheese are not. Fortified orange juice, soy milk and other plant-based beverages, and breakfast can all contribute to vitamin D intake, although the added amounts vary widely among brands.
Vitamin D Food Supplements
Figure 9.12. Food sources of vitamin D. Source: Examples of good sources in the picture include salmon, milk, mushrooms, fortified soy milk, and whole grains. The NIH
To be more effective at increasing circulating vitamin D levels, but others have not found a difference in the effectiveness of the two types.
Human breast milk does not contain enough vitamin D, so the American Academy of Pediatrics recommends that breastfed infants receive a supplement with 400 IU of vitamin D per day until they are weaned from vitamin D-fortified formula or cow’s milk. A vitamin D supplement may also be recommended for older children and adults, depending on diet and sun exposure, but this should be discussed with a healthcare provider.
In children, vitamin D deficiency causes rickets, a disease in which the bones become soft, weak, and deformed. Rickets was very common in the U.S. until the 1930s, when milk processors were asked to add vitamin D to cows’ milk. Milk fortification nearly eradicated rickets from the U.S. and other developed countries. However, rickets can occur in breast-fed babies and in children raised on a vegan diet that cannot be supplied with other sources of vitamin D, especially if they have dark skin.
Functions Of Vitamin D In Human Body And Sources In Food Outline Diagram Stock Vector
Figure 9.13. Vitamin D deficiency in children causes rickets, a disease in which vitamin D deficiency leads to soft, weak, and deformed bones.
In adults, vitamin D deficiency causes osteomalacia, characterized by softening of the bones, reduced bone mineral density, and increased risk of osteoporosis. Because bones are continuously regenerated throughout life, insufficient vitamin D limits the calcium available to continue rebuilding bone tissue. Vitamin D deficiency can also cause bone pain, as well as muscle weakness and pain, symptoms that can increase the risk of falls and fractures, especially in the elderly.
Although vitamin D toxicity is rare, taking too much vitamin D in supplement form can lead to hypercalcemia, or high calcium in the blood. Hypercalcemia can cause kidney damage and calcium deposits to develop in soft tissues such as the kidneys, blood vessels, or other parts of the cardiovascular system. The synthesis of vitamin D from the sun does not cause vitamin D toxicity, because the synthesis of vitamin D is tightly regulated and decreases when the body has too much vitamin D.
Also known as vitamin D3, this form of vitamin D is made by the skin when exposed to UV light and is found in animal-based foods.
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Precursor of the active form of vitamin D; the circulating form of vitamin D and the form measured in the blood to assess a person’s vitamin D status.
Active vitamin D; increases intestinal calcium absorption and works with PTH to release calcium from bones and reduce urinary calcium loss.
A disease caused by vitamin D deficiency in adults and characterized by softening of the bones, reduced bone mineral density, and increased risk of osteoporosis.
Nutrition: Science and Everyday Practice, v. 1.0 Copyright © 2020 by Alice Callahan, PhD; Heather Leonard, Med, RDN; and Tamberly Powell, MS, RDN is licensed under a Creative Commons Attribution-NonCommerce 4.0 International License, unless otherwise noted. You may have heard of Vitamin D. It is often referred to in reference to the sun. You may know that Vitamin D, like all vitamins, is important for your health. However, you may not know exactly what Vitamin D does, how it helps your body, how the sun is involved, and other ways to provide your body with Vitamin D. Read on to learn all about Vitamin D.
Importance Of Vitamin D
Vitamin D is an interesting nutrient. It is a fat-soluble vitamin that acts like a steroid hormone. Vitamin D receptors are found in tissues throughout the human body. Vitamin D is only a vitamin if we don’t get enough sunlight, as we can’t make vitamin D in our skin through sun exposure. Ultraviolet B (UVB) rays interact with cholesterol in our bodies to form Vitamin D components.
Vitamin D production is a complex process in the body. It starts in the skin, where ultraviolet light causes the conversion of the molecule 7-dehydrocholesterol (part of what we call Cholesterol) into pre-vitamin D2. This is then converted to cholecalciferol (also called Vitamin D3). This skin synthesis of Vitamin D3 accounts for 80% of the Vitamin D in our bodies.
Next, in the liver, Vitamin D precursors are converted to 25-hydroxyvitamin D, also known as 25(OH)D for short. This is the main circulating form of Vitamin D, so doctors often test this form of Vitamin D and use the results to determine a patient’s vitamin D status.
Finally, in the kidneys, Vitamin D is converted to calcitriol. This is the active metabolite of Vitamin D, which is what your body uses for its functions. It only circulates in the body for a few hours, which is why we usually don’t think about calcitriol when measuring Vitamin D levels.
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Vitamin D plays a role in regulating more than 200 genes in the body. Vitamin D influences many body functions including cell proliferation, cell division, apoptosis, oxidative stress, membrane transport, matrix homeostasis, tissue mineralization, and cell adhesion.
Functionally, Vitamin D deficiency can have a significant impact on the body and mind
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