Vitamin D refers to a group of fat-soluble secosteroids responsible for enhancing intestinal absorption of calcium, iron, magnesium, phosphate, and zinc. In humans, the most important compounds in this group are vitamin D3 (also known as cholecalciferol) and vitamin D2 (ergocalciferol). Cholecalciferol and ergocalciferol can be ingested from the diet and from supplements. Very few foods contain vitamin D; synthesis of vitamin D (specifically cholecalciferol) in the skin is the major natural source of the vitamin. Dermal synthesis of vitamin D from cholesterol is dependent on sun exposure (specifically UVB radiation).
Vitamin D from the diet or dermal synthesis from sunlight is biologically inactive; activation requires enzymatic conversion (hydroxylation) in the liver and kidney. Evidence indicates the synthesis of vitamin D from sun exposure is regulated by a negative feedback loop that prevents toxicity, but because of uncertainty about the cancer risk from sunlight, no recommendations are issued by the Institute of Medicine (US) for the amount of sun exposure required to meet vitamin D requirements. Accordingly, the Dietary Reference Intake for vitamin D assumes no synthesis occurs and all of a person’s vitamin D is from food intake, although that will rarely occur in practice. As vitamin D is synthesized in adequate amounts by most mammals exposed to sunlight, it is not strictly a vitamin, and may be considered a hormone as its synthesis and activity occur in different locations. Vitamin D has a significant role in calcium homeostasis and metabolism. Its discovery was due to effort to find the dietary substance lacking in rickets (the childhood form of osteomalacia).
Beyond its use to prevent osteomalacia or rickets, the evidence for other health effects of vitamin D supplementation in the general population is inconsistent. The effect of vitamin D supplementation on mortality is not clear, with one meta-analysis finding a decrease in mortality in elderly people, and another concluding no clear justification exists for recommending vitamin D.
Vitamin D is an often-overlooked, under-consumed nutrient that plays a major role in your overall health.
You probably know it as the “sunshine vitamin,” or the vitamin that helps maintain strong bones, but there’s a lot more to Vitamin D than meets the eye. It serves a variety of functions in the body, including maintaining optimal bone and muscle health, as well as having favorable effects on inflammation. Unfortunately, most of us don’t get enough *vitamin D on a daily basis, with a reported one billion people worldwide having a deficiency.
Vitamin D deficiency is a pandemic in the United States, but many Americans, including physicians, are not aware that they may be lacking this important nutrient.
Despite its name, *vitamin D is not a regular vitamin. It’s actually a steroid hormone that you get primarily from either sun exposure or supplementation, and its ability to influence genetic expression that produces many of its wide-ranging health benefits.
Researchers have pointed out that increasing levels of *vitamin D3 among the general population could prevent chronic diseases that claim nearly one million lives throughout the world each year. Incidence of several types of cancer could also be slashed in half.
*Vitamin D also fights infections, including colds and the flu, as it regulates the expression of genes that influence your immune system to attack and destroy bacteria and viruses.
*Vitamin D can be produced in the body with mild sun exposure or consumed in food or supplements.
Adequate *vitamin D intake is important for the regulation of calcium and phosphorus absorption, maintenance of healthy bones and teeth, and is suggested to supply a protective effect against multiple diseases and conditions such as cancer, type 1 diabetes and multiple sclerosis.
Vitamin D has multiple roles in the body, helping to:
Maintain the health of bones and teeth
Support the health of the immune system, brain and nervous system
Regulate insulin levels and aid diabetes management
Support lung function and cardiovascular health
Influence the expression of genes involved in cancer development.
In spite of the name, *vitamin D is considered a pro-hormone and not actually a vitamin. This is because the body is capable of producing its own *vitamin D through the action of sunlight on the skin, while vitamins are nutrients that cannot be synthesized by the body and must be acquired through the diet or supplements.
It is estimated that sensible sun exposure on bare skin for 5-10 minutes 2-3 times per week allows the body the ability to produce sufficient *vitamin D, but *vitamin D has a half-life of only two weeks, meaning that stores can run low, especially in winter. Recent studies have suggested that up to 50% of adults and children worldwide are *vitamin D deficient. There are several likely factors contributing to *vitamin D deficiency, which will be looked at further in this article.