Vitamin D is currently one of the hottest topics in the research and clinics, as well as in everyday life. Vitamin D is a nutrient that the body needs in small amounts to function and stays healthy. Vitamin D is a fat-soluble secosteroid that helps the body use calcium and phosphorus to make strong bones and teeth. It is also produced endogenously when ultraviolet (UV) rays from sunlight strike the skin and trigger vitamin D synthesis. it obtained from sun exposure, foods, and supplements are biologically inert and must undergo two hydroxylations in the body for activation. The first hydroxylation, which occurs in the liver, converts vitamin D to25-hydroxyvitamin D [25(OH)D], also known as “calciferol”. The second hydroxylation occurs primarily in the kidney and forms the physiologically active 1,25-dihydroxy vitamin D, also known as “calcitriol”. A normal individual can absorb dietary calcium between 60 to 80%. Without vitamin D only 10-15% of dietary calcium and about 60% of phosphorus is absorbed. Therefore, vitamin D has a great effect on forming and maintaining strong bones. It has also recently found that vitamin D receptors exist in a variety of cells thus it has a biological effect on more than mineral metabolism.
Recommended Dietary Allowances (RDAs)
In 1997, the Institute of Medicine of the US National Academy of Science recommended the following new adequate intakes for vitamin D as:
400 IU daily for infants less than one year years.
600-800 IU (International units) for for children and adolescents from 1 to 70 years of age.
800 IU for above than 70.
However, the recommended daily value (DV) is 800 IU (20mcg) of vitamin D per day from food. Foods with 15% or higher daily value have a lot of vitamin D. A great number of studies revealed that if u don’t get enough sunlight, then the intake of children and adults requires approximately 1000 IU (25mgc) per day.
Forms of vitamin D
There are two basics types of vitamin D :
1.Ergocalciferol: When ultraviolet rays from the sun hit the leaves of the plants. Ergosterol converted into ergocalciferol, or vitamin D2.
2. Cholecalciferol: Cholecalciferol, or vitamin D3 is formed when 7-dehydrocholesterol in the skin is exposed to solar ultraviolet B ( UVB, 290-320 nm) and then converted to previtamin D3. In heat dependent process, previtamin D3 converted to vitamin D. Excess UVB rays transform previtamin D3 into biologically inactive metabolites, tachysterol, and lumisterol.
Both classes ergocalciferol and cholecalciferol are also naturally occurring forms that are produced in the presence of the sun’s ultraviolet-B (UVB) rays, hence its nickname, “the sunshine vitamin” .but vitamin D2 is produced in plants and fungi and vitamin D3 in animal, including humans.
Vitamin D deficiency occurs when peoples don’t take appropriate dietary intake or exposure to UVB rays. Vitamin D deficiency has been associated with rickets, a disease in which bone tissues don’t properly mineralize, leading to soft bones and skeletal deformities. In addition to bone deformities and pain, severe rickets can cause failure to thrive, developmental delay, hypocalcemic seizures, cardiomyopathy, and dental abnormalities. Low calcifediol (25-hydroxy -vitamin D ) can result from avoiding the sun. Being deficient in vitamin D can cause intestinal absorption of dietary calcium to fall to 15%.
- Rickets: Breastfeeding without vitamin D supplementation can cause rickets in infants. In one Minnesota county, the incident rate of rickets in children younger than 3 years in the decade beginning in 2000 was 24.1 per 100,000. Rickets occurred mainly in black children who were breastfed longer, were born with low birth weight, weighed less, and were shorter than other children.
- Osteomalacia: In adults and adolescents, vitamin D deficiency can lead to osteomalacia, in which existing bones is incompletely or defectively mineralized during the remodeling process, resulting in weak bones Signs and symptoms of osteomalacia are similar to those of rickets and include bone deformities and pain, hypocalcemic seizures, tetanic spasms, and dental abnormalities.
- Oily fishes: Oily or fatty fishes such as Salmon which contain 600-1000 IU per serving (100 grams) or 66% of DV (daily value), Sardines contains 300 IU per serving (100grams) or 39% of the DV, Mackerel contains 250 IU per day serving (100 grams) or 27% of the DV and Canned tuna contains 260 IU per serving (100 grams) which is 34% of DV of the vitamin D3.
- Egg Yolks: are reported to contain 37IU (one egg) or 5% of the DV of vitamin D through the amounts are highly variable.
- Fortified foods: such as soy milk which contains 107-117IU in one cup (237ml) or 13-15% of the DV, Cow milk contains about 115-130 IU per cup (237 ml ) or about 15-22% of the DV, almond milk and oat milk also good sources of the vitamin D.
- Mushrooms: Mushrooms are the only good plant source of vitamin D. Mushrooms can synthesize this vitamin when exposed to UV light. Wild mushrooms contain 2300 IU per serving (100 grams ) or nearly three times the DV.
- Cod liver oil: is also a rich source of foods with 448 IU per teaspoon(4.9 ml ) or 56% of the DV of the vitamin D3.
- Fortified Orange juice: Orange juice in one cup (237 ml ) with breakfast can start your day off with up to 100 IU or 12% of DV of the vitamin D.
- Cereals and oatmeal: Half a cup (78grams ) of cereals and oatmeals can provide 54-136 IU or up to 17% of the DV of the vitamin D.
- Yogurt: Yogurt contains 272 IU (175 grams) or 34% of the DV of vitamin D.
- Broccoli: Broccoli ( boiled/drained) is also a good source which contains 33 mg (125 ml ) per serving of the vitamin D.
- Almond butter: Almond butter contains 180 IU (113mg ) or 22.5% of the DV and 30 ml (2 tablespoons) of calcium and vitamin D.
So we read all about the deficiency symptoms, types, diseases that form from the deficiency of the vitamin D, recommended dietary allowances for each age groups, and the sources of foods which is rich in Vitamin D. Vitamin D is required to maintain the serum calcium concentration within the normal physiologic range for musculoskeletal health (bone health and strong muscles). So we have to take an adequate amount of vitamin D by the recommended dietary value of 400-2000 IU for different age groups from sun exposure and natural sources of the above foods. So we can reduce the deficiency of vitamin D.