There are two reasons that make the vitamin D unique among all the essential nutrients found in the human body. This vitamin is synthesized within the human body when the human skin is exposed to sufficient amounts of sunlight. This vitamin is also regarded as a hormone due to its involvement in the regulation of the functioning of specific organs and tissue systems at a cellular level.
One of the primary roles of the vitamin D in the human body is to boost the rate of absorption of the essential minerals calcium and phosphorus from the intestines - this ensures that the blood levels of these two minerals are always sufficient for proper calcification of bones and cartilaginous tissues. The hormonal role of the vitamin D is in the regulation of the activity of a particular enzyme called 1-ahydroxylase; this enzyme is needed for the conversion of the vitamin D to its active chemical form in the human body. The enzymatic activity of this compound is in turn determined by blood levels of the vitamin D and the mineral calcium. The activity of this enzyme increases whenever the blood levels of calcium and vitamin D start to lower, this increase in enzymatic activity results in the production of more of the metabolically active form of the vitamin in the body. This is a bio-chemical pathway through which the human body is protected against sudden low spots in the intake of calcium and vitamin D and a way in which the body adjusts to a dietary deficit of essential nutrients. The production of sufficient amounts of the metabolically active vitamin in the body can also induce a state of severe calcium deficiency or may trigger a rare toxic overdose of the vitamin D - in such a scenario, stores of calcium in the bones will be mobilized and result in weakening of the skeletal system.
The role of vitamin D in the proper mineralization of bone is another important function performed by the vitamin at the level of the skeletal system. However, very little of the biochemical involved in this mineralization is known and further research is needed to trace out the exact biochemical pathways through which the vitamin works.
As one of the main effects of a deficiency becomes evident in a malfunction in one of the thyroid and pituitary glands, it is believed that the vitamin D plays a vital role in regulating the structure and function of these organs. The vitamin may be necessary for one of the vital biochemical pathways at the cellular level in these tissues.
Elevated blood cholesterol has been found to be reduced if small amounts of vitamin D are supplemented in the diet of a person affected by high blood cholesterol levels. While there is no toxicity associated with the amount of vitamin D necessary to bring on this effect of lowering blood cholesterol. There is almost no knowledge and no recommendation about the levels of supplemental doses of vitamin D required for people with high cholesterol problems.
A great reduction in the absorption of calcium and phosphorous from the intestine also results when a person suffers from a deficiency in vitamin D - the rate of absorption and the utilization of these minerals in the body is controlled by the vitamin. As a deficiency progresses, the levels of these minerals excreted in the urine and fecal matter starts to rise while the levels of these minerals in the blood begins to drop. The result is bone loss of calcium as the body tried to maintain the levels of calcium in the blood - this is necessary for biochemical pathways other than bone mineralization - a lot of calcium begins to be mineralized from the bones. This loss of calcium at a high rate can induce a condition called osteomalacia in adults, the symptom being a softening of the bones in the body due to loss of minerals. The same symptomatic disorder can strike growing children; in children the condition is called rickets. Children are affected differently as the bones in the body are still growing, as the deficiency affects the body calcium and phosphorus are not deposited in the cartilage matrix at a normal rate and the initial cartilage is not replaced as it should be - the result is a swelling in the bones of the body with cartilage still present at the ends and a soft and malformed middle region along long bones. The term rickets is applied when this condition becomes evident in the affected child. There are other symptoms of a vitamin D deficiency during the crucial developmental stage; one result is a thinning and irregular growth in the enamel of the teeth.
High levels of lead in the blood have also been linked to low dietary intake and consequently reduced blood levels of vitamin D and calcium. As the blood and tissue levels of calcium fall, it is believed that the body mobilizes lead from the bones and starts to deposit it in the soft tissues; this accumulation of lead in the tissues is harmful and even lethal for an individual.
Though very easily avoided, a deficiency of vitamin D is surprisingly more common than thought possible. Some of the many contributing factors to a vitamin D deficiency include things like poor dietary intake, an intestinal malabsorption problem, and the result of gastric surgery and an insufficient exposure of the skin to ambient sunlight.
A deficiency of the vitamin D can come about through the use of several different medications, these can interfere with the metabolism of vitamin D in the body, some of these medications are substances such as liquid paraffin when it is taken as a laxative, certain kinds of anti-convulsant medications - namely primidone, phenytoin and phenobarbitone, hypnotic drugs like glutethimide and corticosteroids such as prednisone used in treating other disorders.
Sunlight is the main factor in the formation of vitamin D, for this reason this vitamin is also called the sunshine vitamin as it is formed in the skin. Vitamin D synthesis occurs at the sub-surface levels of the skin on the exposure of bare human skin to ultraviolet light from the sun falling on the skin at the correct wavelength - humans get most of their requirement for vitamin D in this way. Some scientists still raise a question about the relative importance between the two major sources of vitamin D - sunlight or diet. Sunlight for example, is a major factor for vitamin D production in humans as long as the person is in the tropics, and a sunny day in the northern parts of the American continent from March to October can result in the synthesis of as much as 10,000 units of vitamin D in the body. However, this production falls drastically during the winter months and very little of the vitamin D is synthesized in the body. Countries in the far north or places at the southern edges of the world also do not receive sunlight for six months in a year - people living in such areas need supplemental vitamin D to remain healthy.
Unless sunlight is included, good natural sources of the vitamin D are rare. Good sources of the vitamin D include some fish species, particularly the oily fish that possess large quantities of oil in the flesh - like most saltwater fishes, salmon, sardines and herrings. Good sources of vitamin D also include organ meats like liver, egg yolk and milk produced in the summer from dairy cows. At the present time, some processed foods are fortified with synthetic vitamin D and these also can be included as good dietary sources of the vitamin D.
There are a wide variety of dosages of supplemental vitamin D in the market, these doses range from a few units to several hundred units. The main supplemental vitamin D comes in two forms, the vitamin D2 and the vitamin D3. The synthetic form of the vitamin is called D2 - at times, calciferol or activated ergosterol. The D3 form of the vitamin is what occurs naturally in foods and is abundant in products like the fish liver oils.
In winter incidences of vitamin D deficiency are much more common, as there is an insufficient exposure to sunlight during the season especially for people living in the far north - a long term deficiency of the vitamin D can cause abnormal bone formation and bring forth osteomalacia or rickets in adults and children respectively. Strict vegetarians and vegans are also much more likely to suffer from a deficiency of the vitamin - since they may avoid vitamin D-fortified dairy products. Many other groups of individuals are also susceptible to the disorder, these include dark skinned individuals, individuals affected by malabsorption disorders, people with liver disease or kidney disease as well as long term alcoholics. The synthesis of vitamin D cannot occur in a correct way in the bodies of individuals affected by liver and kidney disease and even if sufficient vitamins are produced in the body, the bio-chemical mechanism to activate it simply does not exist.
A vitamin D deficiency is believed to affect at least one in seven adults in most countries around the world. A vitamin D deficiency is believed to affect many hospitalized patients, with a deficiency for those below age 65, standing at about 42% according to the clinical reports. Despite the fact that most persons who were studied were in fact consuming the daily recommended amounts of the vitamin in the diet, this same report went further in stating that 37% of the people eating nutrient rich diets were still deficient in the levels of the vitamin D in the body. A deficiency of the vitamin D is especially common in elderly people.
Supplements of the vitamin D are not required by individuals who get plenty of exposure to sunlight. The synthesis of vitamin D is increased when sunlight strikes bare skin. At the same time, if the vitamin is taken as a supplement, the adult dose considered safe is about 400 IU per person daily.
Vitamin D supplements must not be taken by individuals affected with diseases like sarcoidosis especially if they suffer from elevated blood levels of calcium, this also holds true for all people affected by hyperparathyroidism - a physician must be present to monitor the supplemental regimen. Supplemental regimens that are too long and involve an intake of very large amounts of the vitamin D can induce problems such as headaches, sudden weight loss and cause the development of kidney stones. However, it is rare for other symptoms such as deafness, increase in thirst, visual problems and blindness, an increase in the rate of urination, persistent diarrhea, nervous irritability, or a failure to gain weight in children, and even death to come about - though all these may indeed affect a person on such a high dose supplemental regimen. The usual supplemental regimen taken by most people is about 400 IU of the vitamin daily - this amount is considered a safe amount for adults, at the same time another study showed that taking 800 IU daily of the vitamin prevented bone loss much more effectively than taking 200 IU of the vitamin daily in women who are post-menopause. A physician must be consulted by anyone who wishes to take more than 1,000 IU of the vitamin daily for long periods of time. The crucial information one must remember is that the total daily intake of the vitamin D includes all the vitamin D found in fortified milk and other fortified processed foods, in cod liver oil and all the vitamin D supplements if any, that is consumed. At the same time, the vitamin D required from all sources by individuals who receive adequate exposure to sunlight is not as much as the amount needed by people who receive minimal exposure to sunlight.
The rate of absorption of both calcium and phosphorus is increased by the vitamin D in the body. The absorption of aluminum is also reported to be increased by the vitamin D. Calcium present at higher amounts in the blood can serve as a marker for the vitamin D status of the person and this has been connected to the likelihood of heart disease affecting the person some time in their lifetime. There is also some evidence from research, that vitamin D can possibly increase the blood cholesterol levels in people - this suggestion based on research is not supported by other evidence gathered from other research projects.