Vitamin D is a fat-soluble vitamin that is naturally present in very few foods, it is added to other foods through fortification, and is available as a dietary supplement. It is called the sunshine vitamin because it is produced when ultraviolet rays from the sun strike the skin which triggers vitamin D synthesis. Vitamin D is biologically inert and must undergo two transformations in the body for activation. The first occurs in the liver. The second occurs in the kidneys. It helps the body fight infection, promotes weight loss, reduces depression and some studies show it has relevance in combating certain types of cancer.
People living in higher latitudes like northern US, Canada and Europe, for example, do not get enough natural vitamin D from the sun in the fall and winter months.
Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone. It is also needed for bone growth and bone remodeling.
Vitamin D3, together with vitamin K2 ensure that calcium is absorbed easily and reaches the bone mass, while preventing arterial calcification which helps keep your heart and bones healthy. There are two forms of supplemental vitamin D: vitamin D2 (pre-vitamin D) and vitamin D3 (which is biochemically identical to that which is produced in the body when the skin is exposed to sunlight).
Without sufficient vitamin D, bones can become thin, brittle, or misshapen. Together with calcium, vitamin D also helps protect older adults from osteoporosis.
Symptoms of vitamin D deficiency include:
- Burning in mouth and throat
- Poor bone development
- Abnormal number of dental cavities, cracking teeth
- Osteoporosis (demineralized bone)
- Osteomalacia (softening of bone)
- Rickets (bowlegs or knock-knees)
- Joint pain, bone pain
- Muscular cramps
- Nearsightedness, myopia
- Nervousness
- Insomnia
- Constipation
Sources of vitamin D include sunlight, cod liver oil, egg yolks, liver, herring, sardines, salmon, tuna, and organ meats.
Recommendations for supplementation vary widely from 400 - 2000 IU/day and much higher.