Vitamin D – also called the “sunshine vitamin” – is one of the fat-soluble vitamins. Not just one substance, vitamin D refers to several related fat-soluble sterol (cholesterol-like) micronutrients.
Vitamin D Production
Vitamin D is actually manufactured in the human skin when it is exposed to the ultraviolet spectrum of the sun’s rays. Sun exposure triggers a chemical reaction with a 7-dehydrocholesterol (a form of cholesterol), which is subsequently transferred to the liver or kidneys and converted to calcidiol, a (less active) form of vitamin. Calcidiol from the liver is then transported to the kidneys for conversion into calcitriol or D3, the most fully active form of vitamin D.
RDA Vitamin D
Most of our vitamin D needs are met with regular sun exposure and food sources. Increased intake or supplementation may be required if sunlight is diminished (i.e. during winter months, if we live cities where light is blocked by buildings or smog), and for those with dark skin, or whose skin is not regularly exposed to sunlight.
No specific RDAs for vitamin D have been set due to insufficient research evidence. AI (adequate intake) levels have been set at:
- 200 IU for males and females (including pregnant and lactating females) from birth to age 50
- 400 IU for men and women aged 51 to 70
- 600 IU for men and women above age 70
Sources of Vitamin D
While there are both plant- and animal-derived sources of vitamin D, only animal sources are cholesterol-based and can be converted in the body to its fully active form, natural or D3. Also, plant foods tend to contain very low amounts of the plant version, vitamin D2.
Food sources include:
- Fish liver oil (i.e. cod liver oil)
- Egg yolks
- Homogenized milk, and butter
- Oily fish flesh (i.e. mackerel, salmon, sardines, herring)
- Fortified breakfast cereals
- Dark leafy greens
Vitamin D Deficiency Symptoms
Vitamin D helps regulate the metabolism and use of the minerals calcium and phosphorus, which together (along with other minerals) make up our bones. Vitamin D is essential for helping us maintain strong bones and teeth, as well as balanced blood levels of calcium and phosphorus, which also contribute to healthy nervous systems and heart functioning, and blood clotting.
Deficiency in vitamin D causes blood calcium and phosphorus levels to drop, triggering the body to leach these minerals from the bones and teeth.
Symptoms of deficiency include:
- Rickets (pediatric) – compromised growth/development leading to soft skull bones, fragile other bones, bowed legs, spinal curvature, large joints, and diminished muscular development.
- Adult Rickets (Osteomalacia) – weak bones and bone loss due to loss of bone mineral
- Osteoporosis – weak, porous bones and bone loss due to loss of bone mineral and proteins
- Poor dental health, including tooth decay and gum problems
- Nearsightedness (myopia) and hearing loss due to vitamin D’s influence on the eye muscles and deterioration of the tiny bones of the inner ear (responsible for transmitting sound).
Vitamin D Toxicity
Stored not just in the liver, but also in the skin, brain, spleen and bones, many authorities consider vitamin D to be the most potentially toxic vitamin.
Mild symptoms of vitamin D toxicity include excessive thirst, diarrhea, nausea, weakness, and headaches.
More serious symptoms include increased calcium and phosphorus blood and urine levels, abnormal calcification of soft tissues, and (perhaps) aggravated atherosclerosis. Toxicity can easily occur when vitamin D is taken in large amounts (more than 1000 to 1500 IU daily for a month or longer in adults) or with excessive sun exposure (sun poisoning).
Recently, researchers have suggested supplementation of vitamin D in the prevention and treatment of various cancers due to its involvement in the regulation of cell division, growth and numbers.
Before you reach for a zinc supplement, consider whether your needs could be adequately met by dietary zinc sources, which are (as with most supplements) the best form. Consult with your health care practitioner before beginning a regimen of therapeutic zinc supplementation, particularly if you are pregnant or lactating, or if you have pre-existing health conditions.