WHERE CAN VITAMIN D BE FOUND?
Very few natural foods contain Vitamin D. Fatty fish such as salmon, tuna and mackerel, as well as fish live oils are among the best sources. Minute amounts of Vitamin D are found in liver, cheese and egg yolk. Also, certain mushrooms provide Vitamin D in variable amounts. Ready-to-eat breakfast cereals are fortified with Vitamin D, as are some brands of orange juice, yogurt, margarine and other food products.
Vitamin D in its primary form, found in food, is inactive and gets converted to its metabolite i.e., 25(OH) Vitamin D, in the liver. This 25(OH) Vitamin D is converted into its active form, 1,25 (OH) Vitamin D, by the kidneys.
Nude at Noon
In this day and age, most people meet at least some of their Vitamin D needs through exposure to sunlight. Season, time of day, length of day, cloud cover, smog, skin melanin content and sunscreen are among the factors that affect UV radiation exposure and Vitamin D synthesis.
Complete cloud cover reduces UV energy by 50%; shade (including that produced by severe pollution) reduces it by 60%. UVB radiation does not penetrate glass; so exposure to sunshine indoors through a window does not produce Vitamin D. Sunscreens with a sun protection factor (SPF) of 15 or more appear to block Vitamin D-producing UV rays. It has been suggested by some Vitamin D researchers that approximately 5–30 minutes of sun exposure between 10AM and 3PM at least twice a week to the face, arms, legs, or back without sunscreen usually lead to sufficient Vitamin D synthesis. Individuals with limited sun exposure need to include good sources of Vitamin D in their diet or take a supplement to achieve recommended levels of the Vitamin.
DIETARY VITAMIN D SUPPLEMENTS
In supplements and fortified foods, Vitamin D is available in two forms: D2 (Ergocalciferol) and D3 (Cholecalciferol). Chemically, they differ only in their side-chain structure. The two forms have traditionally been regarded as equivalent based on their ability to cure rickets and, indeed, most steps involved in the metabolism and actions of Vitamin D2 and Vitamin D3 are identical. Both forms (as well as Vitamin D in foods and from cutaneous synthesis) effectively raise serum 25(OH)D levels. However, Vitamin D3 is more potent than Vitamin D2.
VITAMIN D DEFICIENCY
Vitamin D deficiency is fairly common. It can occur when
- Usual intake is lower than recommended levels over a period of time.
- Exposure to sunlight is limited
- Kidneys are unable to convert 25(OH) Vitamin D into the active form 1,25(OH) Vitamin D
- Absorption of Vitamin D by the digestive tract is inadequate
In adults, Vitamin D deficiency can lead to osteomalacia, resulting in weak bones. Symptoms of bone pain and muscle weakness can indicate inadequate Vitamin D levels, but such symptoms can be subtle and go undetected in the initial stages.