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Vitamins
Vitamin D, sunlight and skin color
There are several forms of the vitamin. Vitamin D2 is derived from ergosterol in the diet, whereas vitamin D3 is derived from cholesterol via 7-dehydrocholesterol. Ultraviolet light (UVB which is wavelengths from 290 to 315 nm sunlight is responsible for the production of the vitamin- 20,000 IU in one minimal erythemal dose of exposure.) However, in certain parts of the world with reduced sunlight intensity there is the possibility that the quantity of vitamin D is not always sufficient. To prevent this possibility, milk may be fortified with vitamin D2. A deficiency of vitamin D leads to rickets which is a softening of the bones owing to faulty mineralization.
The active form of the vitamin is calcitriol which is synthesized from either D2 or D3 in the kidneys. Calcitriol binds to a protein transcription factor which then regulates gene expression. The outcome is the maintenance of calcium and phosphorus levels in the bone and blood with the assistance of parathyroid hormone and calcitonin.
Vitamin D deficiency is also known to cause:
Osteoporosis: A condition characterized by fragile bones.
Osteomalacia: A bone-thinning disorder in adults that is similar to rickets.
Vitamin D malnutrition may also be linked to chronic diseases such as cancer (breast, ovarian, colon, prostate, lung and skin), chronic pain, weakness, chronic fatigue, autoimmune diseases like multiple sclerosis and Type 1 diabetes, high blood pressure, mental illnesses (depression, seasonal affective disorder and possibly schizophrenia) heart disease, rheumatoid arthritis, psoriasis, tuberculosis, periodontal disease and inflammatory bowel disease.
Vitamin D food sources
Fortified foods are the major dietary sources of vitamin D. Prior to the fortification of milk products in the 1930s, rickets was a major public health problem. In the United States milk is fortified with 10 micrograms (400 IU) of vitamin D per quart, and rickets is now uncommon in the US .
One cup of vitamin D fortified milk supplies about one-fourth of the estimated daily need for this vitamin for adults. Although milk is fortified with vitamin D, dairy products made from milk such as cheese, yogurt, and ice cream are generally not fortified with vitamin D. Only a few foods naturally contain significant amounts of vitamin D, including:
fish oils such as cod liver oil, 1 Tbs., 1,360 IU
fatty fish such as salmon, cooked, 3.5 oz, 360 IU
mackerel, cooked, 3.5 oz, 345 IU
sardines, canned in oil, drained, 3.5 oz, 270 IU
eel, cooked, 3.5 oz, 200 IU
one whole egg, 25 IU
Beef liver, cooked, 3½ ounces 15 IU
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