Benefits of Vitamin D, Types and their physiological functions
Vitamin D, actually, is not considered a vitamin in the strict sense of the word. Vitamins are nutrients because they come from food, but the situation is different with vitamin D. The body can get this vitamin from sunlight, as the skin makes it after exposure to sunlight. Vitamin D that we get, whether from the sun or from food, is called vitamin D3. Vitamin D3 is not biologically active, it needs be converted to the active form, which is done in the liver and kidneys. See the image below.
The critical importance of Vitamin D is not due not only to its importance in maintaining bone health (which is the most well-known function of this hormone, regulation of calcium and phosphorous metabolism), but also to maintaining the health of the entire body.
Metabolism of Vitamin D
Vitamin D has no biological activity in our bodies. Therefore, it must be converted within the body to the active form, known as 1,25-dihydroxycholecalciferol (also called 1,25DHCC) , that occurs in two steps, as shown in the diagram above:
1- First step take place in the liver, where hydroxylation of vitamin D3 (cholecalciferol) takes place to produce 25-hydroxycholecalciferol, ( also know as 25DHCC).
2-Second step in the kidneys, where 25-hydroxycholecalciferol is converted to 1,25-dihydroxycholecalciferol, the biologically active form.
Control of Vitamin D production
The hepatic synthesis of 25-hydroxycholecalciferol is slightly regulated, so blood levels of 25-hydroxycholecalciferol largely represent the amount of vitamin D produced in the skin or from food. However, in the kidneys it is precisely controlled by an enzyme called (1-alpha-hydroxylase). That hormone is controlled by Parathyroid hormone (PTH) secreted by parathyroid gland.
An interesting fact: Humans differ from other types of creatures in the way they manufacture vitamin D, which comes from the sun. In human skin (as well as horses, pigs, rats, cattle, and sheep), there are sufficient quantities of 7-dihydrocholesterol that is converted into cholecalciferol (vitamin D3). But in other species, such as dog and cat skin, there are little amounts of 7-dihydrocholesterol, and its conversion to cholecalciferol is not enough. Therefore, these dogs and cats depend on food as an essential source of the vitamin D.
Benefits of Vitamin D
1- To carry out body vital functions:
The physiological function that explains the Benefits of Vitamin D, and which we know clearly in details, is calcium and phosphorous levels regulation and keeping them in optimum levels in the body, thus achieving adequate mineralization of the skeleton, in order to maintain its strength and safety.
Vitamin D is necessary to absorb calcium from the digestive system (intestine). Severe deficiency of Vitamin D leads to bone disease. In children, severe deficiency results in a disease called rickets, as well as osteoporosis and deformation of the bones. In adults, it can cause osteomalacia.
2-Protection from diseases:
The body needs vitamin D not only for the integrity of the bones, but also to enable the body to perform other vital functions. Vitamin D helps support the immune system, muscular nervous system, and also has an important role our cells.
Research has shown Benefits of Vitamin D in treatment cancers, such as breast cancer, colon cancer, and prostate cancer, as well as in treatment of heart disease, depression, excess weight gain, and many other diseases that have been linked to vitamin D deficiency. Research has shown that people with good levels of vitamin D are less likely to have such diseases, yet there is no conclusive scientific evidence that vitamin D deficiency causes those diseases, (meaning that not everyone with vitamin D deficiency develops such diseases).
Based on the foregoing, treatment with vitamin D may help cure many diseases such as autism, autoimmune disorders, cancer, depression, diabetes, heart disease and high blood pressure. However, these benefits have not been proven by solid scientific data, except for the role of vitamin D helping calcium and phosphorous build strong bones.
How do you get enough from vitamin D?
After learning the Benefits of Vitamin D for our bodies, we have to learn how to obtain it in sufficient amounts from nature. GOD provided the human body with the ability to manufacture some vital elements and nutrients on its own, without completely relying on external sources. One of those vital nutrients is vitamin D, which can synthesized by the skin, using sunlight. Those living in the north of the globe, have a true problem, as the sun does not shine except few months in a year. Also those who are used to live indoors, in their homes and offices, will not have enough exposure to sun rays.
People with dark skin also have a problem. Dark skin absorbs less amount of sunlight compared to light skin. People with dark skin don’t get the same amount of Vitamin D from sun exposure as people with fair skin.
How can I get enough vitamin D?
Getting enough of vitamin D is essential for maintaining bone health and maintaining body health in general, such as controlling weight gain and improving brain function, among others, as was mentioned at the beginning of this article. Then, what are the best natural sources and foods to get vitamin D?
1- Exposure to the sun
15 minutes of exposure to sunlight a day, or half an hour at least twice a week, gives the body a good amount of vitamin D. But this direct exposure to sunlight may expose you to health risks, due to dangerous UV rays, (in large amounts), may cause cancer.
2- From foods and nutritional supplements
There are three top foods, rich in vitamin D: salmon, mackerel, and tuna.
Other food sources of vitamin D:
– Cod liver oil, which is fish oil supplement rich in omega-3 fatty acids. Omega-3 has many health benefits, including reducing inflammation and lowering blood pressure. Cod liver oil, also, contains vitamins A and D, both of which have many health benefits.
– Sardines
– Eggs (egg yolk)
– Dairy products, such as milk or yogurt, and cheese
– Beef liver and calves
Vitamin D levels in the body
25HCC, which is produced by the liver, is not the active form of vitamin D, yet it is the only form of vitamin D that is measured to determine if a person is deficient in vitamin D, has adequate levels, or if toxicity is caused by too much vitamin. 25HCC is the type that transports vitamin D and has a half-life of about 2-3 weeks. 25-HCC equals total vitamin D from exposure to sunlight and that of food. Thus it is considered a true measure of the status of vitamin D in the body.
Why don’t we use the active form to check for vitamin D status?
Although 1,25DHCC is the biologically active form of vitamin D, thus, it stands to reason that it would be the best for measuring the vitamin D status in the body. Practically not so, why?
There are several reasons for this: First, its half-life is very short, a few hours (only 4-6 hours). Moreover, its blood levels are 1,000 times lower than that of 25HCC. And another very important reason, the level may be normal (or perhaps above normal) in some people who suffer from a deficiency in vitamin (D). Explain this in the next paragraph.
In cases of vitamin D deficiency, there is a decrease in the absorption of calcium in the intestine, which reduces the ionized calcium in the body. This is recognized by the calcium sensor in the parathyroid glands, to increase the production and secretion of the parathyroid hormone (PTH), which increases a number of processes: it increases the reabsorption of calcium in the kidneys, and increases the calcium mobilization in the skeleton. It also increases kidney production by 1.25DHCC. Therefore, when a vitamin D deficiency occurs, the compensatory increase in parathormone causes levels of 1,25DHCC to be normal or possibly elevated. Therefore, its determination is not useful as a measure of vitamin D status.
Measurement of Vitamin D levels
There are several laboratory techniques available for measuring 25-HCC, the best of which is by high pressure liquid chromatography (HPLC), but it is a complex technique and not available in all laboratories. So instead, we can use other, simpler methods such as immunochemical luminescence.
Normal Vitamin D Level (25-HCC) :
Normal vitamin D levels vary a lot, however, most experts agree that anyone with a 25-HCC level less than 10 ng/ml is considered severely deficient, and that of 80 ng/ml or more is an excess that may cause health problems. The ideal level for 25DHCC is between 30 and 80 ng/ml as shown in the image below.
Vitamin D deficiency
Why is vitamin D deficiency very common? Many people have vitamin D deficiency due to many reasons including: lack of exposure to sun rays, dark skin, covered skin (in religious people), and nutritional deficiencies, as well as due to old age and habitual indoors stay. Chronic kidney disease or malabsorption in the digestive system , can cause vitamin D deficiency.
Vitamin D deficiency causes demineralization (calcium and phosphorous) from the bones and leads to osteoporosis. Symptoms depend on the age, as children and adults differ.
Symptoms in children
The first clinical manifestation of vitamin D deficiency in children is hypocalcemia , low calcium levels. Hypocalcemia requires immediate treatment with calcium. Then, the child will suffer from bowed legs, which is a sign of rickets.
Symptoms in adults
Usually, vitamin D deficiency in adults is detected upon examination for various symptoms, not including bone, such as lethargy and low mood, and also during examinations to find out the high level of thyroid hormone. However, severe vitamin D deficiency leads to symptoms such as osteomalacia and may lead to a wobbly gait. Severe osteomalacia may cause deficiency of calcium in the blood.
Medical terms:
Rickets = rickets
Osteomalacia = osteomalacia
demineralization = removing mineral
Sources and References:
https://pubmed.ncbi.nlm.nih.gov/16563471/
https://www.mayoclinicproceedings.org/article/S0025-6196(12)64791-0/fulltext
https://www.webmd.com/osteoporosis/features/the-truth-about-vitamin-d-why-you-need-vitamin-d
https://www.health.harvard.edu/blog/vitamin-d-whats-right-level-2016121910893
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2912737/
