Natural Sources of Vitamin D

Vitamin D plays a vital role in maintaining healthy bones, supporting immune function, and regulating several metabolic processes. However, diet alone is not considered a major source of this nutrient. Even a well-balanced diet may fall short of providing the amount required to prevent deficiency, making it important to understand where vitamin D comes from and how the body uses it.

A few foods naturally contain small amounts of vitamin D. Oily fish such as salmon, mackerel, sardines, and bluefish remain among the richest natural dietary sources. Cod liver oil, although less commonly consumed today, continues to stand out as one of the most concentrated natural sources of vitamin D. The two primary forms of this vitamin—vitamin D₂ (ergocalciferol) and vitamin D₃ (cholecalciferol)—occur naturally in different sources: D₂ is typically found in yeast and some fungi, while D₃ is abundant in fish liver oils. Small amounts of vitamin D can also be found in vegetables, meat, and egg yolks, but these contributions are minimal.

Because natural food sources are limited, many countries rely on fortified foods to help prevent vitamin D deficiency. Milk has become the most practical carrier because it is widely consumed and easy to enrich with crystalline vitamin D. Other fortified products may include breakfast cereals, margarine, and plant-based milk alternatives.

Despite the value of dietary and fortified sources, the most efficient source of vitamin D is sunlight. When skin is exposed to ultraviolet-B (UVB) radiation, it converts a naturally occurring pro-vitamin into vitamin D₃, which the kidneys can later activate. For most healthy individuals, sunlight can provide 90–100% of their vitamin D requirement, depending on skin type, geographic location, and time spent outdoors. Like other fat-soluble vitamins, sunlight-derived vitamin D can be stored in the liver for future use.

Vitamin D supplements offer another important option, especially for individuals with limited sun exposure. Many multivitamins contain around 400 IU of vitamin D, while higher-dose preparations—sometimes up to 50,000 IU—are available under medical supervision for treating deficiencies.
Natural Sources of Vitamin D

Vitamin D deficiency and rickets

Vitamin D helps child's body absorb calcium and phosphorus from food. Not enough vitamin D makes it difficult to maintain proper calcium and phosphorus levels in bones.

Vitamin D (where D represents D2 or D3) is biologically inert and metabolized in the liver to 25-hydroxyvitamin D [25(OH)D], the major circulating form of vitamin D that is used to determine vitamin D status.

In an infant or child this deficiency results in the disease called rickets. Rickets is the softening and weakening of bones in children, usually because of an extreme and prolonged vitamin D deficiency. Rare inherited problems also can cause rickets.

Affected children lack the exposure to ultraviolet light necessary for the dermal synthesis of vitamin D and have a poor diet in vitamin D in which the component (high fiber and high cereal) probably contribute to the excessive breakdown of vitamin D.

Symptoms of vitamin D deficiency rickets include restlessness, lack of sleep, slow growth, a delay in crawling, sitting or walking, soft skull bones, swelling of the skull, bead-like nodules where the ribs and their cartilages join, and a delay in the closing of the skull bones.

In adults, the same disorder is called osteomalacia or adult rickets. It is to be distinguished from osteoporosis where bone mass is decreased from hypophosphatemic osteopeniaof premature infants, and from renal osteodystrophy.

The name rickets is from the Old English wrickken, to twist. The more technical medical term, rachitis, which comes from Greek, the spine , was suggested by Francis Glisson in 1650.

Vitamin D deficiency rickets occurs in underprivileged populations throughout the world. It is more common in children of Asian, African-Caribbean and Middle Eastern origin because their skin is darker and needs more sunlight to get enough vitamin D.

Women in United States usually take multivitamins and eat vitamin D dairy foods so rickets and vitamin D deficiency is less a problem than in developing countries and northern Europe.
Vitamin D deficiency and rickets

Vitamin D in general

Vitamin D is different from all other fat-soluble vitamins, in that the body can synthesize it with the help of sunlight, from a precursor that the body makes from cholesterol.Vitamin D, also known as calciferol, is a fat-soluble vitamin.

It occurs naturally in food and human body can also produce it when human skin is exposed to sunlight. Skin synthesis is limited by various determinants, including pigmentation, age, zenith angle of the sun, poor air quality and % of the skin surface area available for exposure.

The two major physiologically relevant forms of vitamin D are D2 (ergocalciferol) and D3 (cholecalciferol). Vitamin D3 is photosynthesized in the skin of vertebrates by the action of solar ultraviolet (UV) B radiation on 7-dehydrocholesterol. Vitamin D2 is produced by UV irradiation of ergosterol, which occurs in molds, yeast, and higher-order plants.

Almost all of the U.S. milk supply is fortified with about 3 mcg (120 IU) vitamin D per cup. Many plant-based alternatives such as soy milk, almond milk, and oat milk are similarly fortified.

Vitamin D is added to many breakfast cereals and to some brands of orange juice, yogurt, margarine, and other food products.

There are some dietary sources of vitamin D. Fatty fish such as salmon, tuna, and mackerel are among the best sources. Beef liver, egg yolks, and cheese have small amounts of vitamin D.

It has long been known to help the body absorb and retain calcium and phosphorus; both are critical for building bone. Vitamin D sustains the normal mineralization of bone, muscle contraction, nerve conduction and general cellular function in all cells of the body.
Vitamin D in general

Vitamin D2 (ergocalciferol)

Food sources of vitamin D

Vitamin D is a nutrient involved in regulating serum calcium. Since milk, human as well as cow’s, is not a good source of vitamin D, a small supplement is required for both breast-fed and bottle-fed infants.

Fish liver oil preparations are normally used as supplements for the supply of vitamins A and D.

Food sources of vitamin D come in natural and fortified forms. Fortified forms are included in milk, cereals, and some margarines.

The chief food sources of vitamin D in western diet are fortified milk and cereals, and fatty fish. Natural sources include fish oils, salmon, sardines, herring, egg yolks and liver. Two basic substances with vitamin D activity, D2 and D3, occur only in yeast and fish liver oils.

Mushroom also contain a small amount of vitamin D. This include mushroom shiitake and maitake mushroom – when they are dried outdoors such as under the summer sun for six and eight hours.
Food sources of vitamin D

What are the roles of vitamin D in human body?

Vitamin D (calciferol or activated ergosterol) is fat soluble. Since vitamin D can be produced in human bodies by the action of sunlight on the skin, many experts consider it to be more of a hormone than a vitamin.

Calcium in milk that help bones strong but without the vitamin D or calciferol, that’s also added to milk, the calcium won’t work.

Vitamin D is responsible chiefly for regulating the absorption and use of calcium and phosphorus.

This vitamin is promotes and maintains normal tooth and bone formation.

Other important functions of vitamin D include maintaining normal nerve conduction and muscle contractions, especially those of the heart muscle.  Calcium is to send messages along body nerves and to help muscles contract. Vitamin D regulates the amount of calcium in blood and makes sure it always enough.

Immune system needs vitamin D, and it may help prevent cancer, especially colon cancer.

Adequate vitamin D is also important during reproduction and lactation. Extreme deficiencies may result in congenital malformation of the newborn and injury to the skeleton of the mother.
What are the roles of vitamin D in human body?

What is vitamin D?

Vitamin D is not a vitamin in the strict definition because it can be produced by exposure of the skin to sunlight.

Vitamin D is synthesized in the skin from 7-dehydrocholesterol (provitamin D3 or pro D3) which is derived from cholesterol. 

While a majority of cholesterols are synthesized in the liver, some cholesterol such 7-dehydrocholesterol are made in the skin.

Vitamin D is created when adequate exposure to sunlight (ultraviolet light-B) is available to promote the synthesis of vitamin D in the skin from 7-dehydrocholesterol.

It is a fat soluble steroid hormone precursor that contributes to the maintenance of normal levels of calcium in the blood stream by increasing absorption of calcium from food and reducing urinary calcium loss (reabsorption by the kidneys).

Both effects keep calcium in the body and therefore spare the calcium that is stored in bones. When necessary, vitamin D transfers calcium from the bone into the bloodstream, which does not benefit bones. 

The bones grow denser and stronger as they absorb and deposit the calcium.

Although the overall effect of vitamin D on the bones is complicated, some vitamin D is necessary for healthy bones and teeth.

Other major physiological function is vitamin D is to maintain extracellular fluid concentrations of calcium and phosphorus within a normal range.

Nutritional vitamin D becomes essential when sunlight is insufficient to meet daily needs. This has become particularly acute as more people reside in urban centers where they are exposed to suboptimal level of sunlight.
What is vitamin D?