Vitamin D.
Vitamin D is a fat-soluble coenzyme. Although it has been classified as  vitamin and can be found in certain foods, vitamin D is not considered essential, since it is synthesized within the body. Vitamin D is a rare example of a nutrient than could be characterized as hormone as well.
Occasionally, vitamin D is described as "sunshine vitamin", because it is produced in the skin after exposure to the ultraviolet (UV) rays of the sunlight. In this process, vitamin D precursors are converted to cholecalciferol. Although there are numerous different chemical forms of vitamin D, cholecalciferol is the most effective for humans and after it is digested from foods or synthesized in the skin, is transformed in the liver and kidneys to dihydroxyvitamin D and it is utilized as hormone. It has been estimated that if half of the body surface is exposed to the sun for nearly half an hour per week without any sunscreen, adequate amounts of vitamin D can be produced. Studies have given evidence that elderly and people with dark skin synthesize less vitamin D than younger and fair people respectively.
Vitamin D increases the absorption of calcium and phosphorus within the intestine and controls the blood levels of these substances. Since both of them and especially calcium are extremely important for good formation of bones, low levels of vitamin D can lead to skeletal diseases. Researchers have found evidence that steroids and caffeine can impair the absorption of vitamin D.
Vitamin D helps in good function of the immune and nervous system, muscle contraction, proper cell growth and functional distinction of them. Vitamin D is a protective factor against multiple sclerosis, hypertension and colorectal cancer. It can, also, ease symptoms of osteoarthritis and psoriasis.
Studies have given evidence that vitamin D in combination with calcium and magnesium can prevent postmenopausal osteoporosis and bone fractures in elderly people. Click this link to be guided, how to find multi-supplements, containing all three nutrients online.
Sources of vitamin D.
The dietary sources of vitamin D are quite limited. It can be found in cod liver oil, oysters, salmon, mackerel, tuna fish and fortified products, such as milk, margarine and breakfast cereals. Small amounts are contained in liver and egg yolks.
It is obvious that a person may have some difficulty to obtain adequate amounts of vitamin D from foods. Thus, people who do not get exposed to the sunlight regularly, either due to their lifestyle or to weather conditions in the area they live, may need vitamin D supplementation to meet the optimum requirements for good health. Other groups that possibly need relevant food supplements are exclusively breastfed infants, postmenopausal women, elderly, people with dark skin and individuals who suffer fat malabsorption, pancreatic secretion disorders, cystic fibrosis, Crohn's disease, celiac disease and liver conditions.
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Vitamin D deficiency and toxicity.
Vitamin D deficiency results in decline of bone density because of impaired absorption of calcium and phosphorus. Vitamin D deficiency can lead to rickets, in children and osteoporosis, in adults, especially postmenstrual females. The former condition involves inadequate mineralization, poor formation, softening and weakening of the bones. Osteoporosis increases the risk for accidental or automatic bone fracture and may results in gradual posture changes.
Since vitamin D is fat-soluble, can be stored and built up to toxic levels. Excessive dosages of vitamin D can result in increased calcium absorption within the gastrointestinal system. This leads to elevated levels of the mineral in the bloodstream. Increased blood calcium level may cause calcium deposition in soft tissues such as the heart and lungs. This, in turn, can reduce the ability of these organs to function properly.
Kidney stones, vomiting, and muscle weakness are the consequences that may occur due to the intake of excessive amounts of vitamin D. You can find more information about vitamin D toxicity by visiting the relevant page.
Vitamin D deficiency may be an aftermath of certain causes presented below.
 Poor dietary intake. People who follow low-fat diets, exclusively breastfed neonates, children and adolescents who drink very little amounts of milk or suffer lactose intolerance syndrome and strict vegetarians have increased chances to encounter vitamin D deficiency.
Fat malabsorption. This is a disorder of the gastrointestinal track which does not allow adequate quantities of fats to be digested. In turn, this results in low absorption of vitamin D, since the latest is contained in fatty foods.
Inadequate exposure to sunlight. As it has been already explained, individuals, who do not get exposed at least half an hour to the sunlight, may have low levels of vitamin D. Low levels of vitamin D may reduce insulin secretion and increase the risk for type 2 diabetes. Researches in San Diego have confirmed that children, who live in areas with low rates of sunshine, are more prone to suffer type 1 diabetes than others, because their body cannot produce adequate amounts of vitamin D.
Impaired metabolic action of kidneys. In cases of reduced ability of the kidneys to transform cholecalciferol to the active form dihydroxyvitamin D, deficiency may develop. Elderly people are more prone to such a problem.
Recommendations for vitamin D.
Surveys have shown that nearly 50% of women in the USA do not take enough amounts of vitamin D. The adequate intake (AI), for cholecalciferol is ranging from 5 to 15mcg/day or 200 to 600 IU/day respectively, depending on the age and medical history of the individual and the availability of sunlight in the area he/she lives. The adequate intake (AI) has been established by the Institute of Medicine of the National Academy of Sciences.
In general, a daily dose of 400 IU seems to be well accepted and safe. If combined with calcium, vitamin D can improve bone density and prevent osteoporosis.
For people beyond the age of seventy and postmenstrual women, 800 IU per day are recommended.
This dose should not be exceeded in pregnant women. When it comes to supplementation that provides more than 400 IU of vitamin D, a doctor’s advice may be needed, in order hypervitaminosis and toxicity to be prevented. |
