Vitamin D is both a hormone and a vitamin, and it plays an important role in control of calcium concentration in the body. Whether as a hormone produced in the skin by the action of sunlight, or as a vitamin provided in the food, vitamin D has to be chemically modified by two processes, which occur sequentially in the liver (where it is stored as 25-hydroxy vitamin D) and the kineys, before it can play an active role in calcium distribution as 1,25-dihydroxy vitamin D.
Vitamin D is best known for its ability to stimulate the absorption of calcium, thus providing anticancer effect, especially in breast, lung, colorectal and prostate cancer, as well as malignant lymphoma and melanoma (skin cancer). As such, it is added to milk and other foods. Disorders of the liver or kidneys result in poor production of vitamin D.
Vitamin D Deficiency
Vitamin D Deficiency can cause rickets in children and osteomalacia in adults. Rickets and osteomalacia are diseases in which bones soften and weaken because there's not enough vitamin D to help the body absorb calcium and phosphorus from food. Symptoms include fatigue, weakness and aching bones, and they go worse as the disease progresses. Fortunately, osteomalacia responds well to daily doses of sunshine and physician-supervised vitamin D therapy. Once common, these diseases are now very rare.
Vitamin D, Heart Disease, Psoriasis and Blood Pressure Levels
In a large study conducted for over 11 years which involved 10,000 women over the age of 65 researchers found that the risk of heart disease death was 31 percent lower in the women who were taking vitamin D supplements at the time of the study. In this study of over 300 women, younger women who consumed at least 400 IU of vitamin D/day had lower blood pressure (they also had significantly higher calcium and potassium intake). It has also been found that small oral doses and topical treatment of vitamin D can improve the symptoms of psoriasis and that the lower the levels of vitamin D in the blood, the more severe the disease.
Rich Food Sources of Vitamin D
Rich food sources of vitamin D are cod-liver oil; cold-water fish such as mackerel, salmon and herring; butter and egg yolks. Vegetables are low in vitamin D.
Vitamin D Quick Calculator
To compensate a possible low level of vitamin D, make sure your food includes healthy portions of meat cold-water fish. Here is a selection of some foods containing vitamin D:
- Cod Liver Oil (3.5 oz) - 1,360 IU
- Sardines, canned in oil, drained (3.5 oz) - 500 IU
- Salmon, cooked (3.5 oz) - 360 IU
- Mackerel (3.5 oz) - 345 IU
- Tuna fish, canned in oil (3.5 oz) - 200 IU
- Milk, vitamin D fortified (1 cup) - 98 IU
- Egg (1 whole) - 20 IU
- Cheese, Swiss (1 oz) - 12 IU
- Whole milk (1 cup) - 227 IU
Bioavailability of Vitamin D
Bioavailability is the percentage of a nutrient absorbed from the food. Nutrients consumed but not released during the digestive process for absorption have no nutritional value. The average relative bioavailability of vitamin D from meat sources is estimated to be 60% as compared with a vitamin supplement. Vitamin D given with milk has been reported to be 3-10 times more potent than that given in oil. The American Society for Clinical Nurition recommended mushrooms as a natural source of vitamin D. Alcoholics and smokers usually have low levels of vitamin D.
High Dosages of Vitamin D Can Be Toxic
The dose makes the medicine. At present, the Recommended Dietary Allowance (RDA) for adults for vitamin D is 400 IU (10 micrograms). However, in light of new data on the metabolism of vitamin D in the absence of sun exposure, some experts suggest a mean requirement of at least 500 IU (12.5 microg) for adults. Others suggest even a much higher dosage of 2,000 IU/day .
You should be aware of the fact that prolonged continued intake of any vitamins known to be toxic if taken in high dosages can result in serious health damage. In case of vitamin D overdosage, it can cause hypercalcemia (deposition of calcium in soft tissues (especially the kineys, heart, ling, and blood vessels), hyperphosphatemia, and hypercalciuria (presence of excess calcium in the urine). In high dosages, vitamin D is the most toxic of all oil-soluble vitamins. Consult your primary care physician before taking supplements of vitamin D.