Vitamin D: The Versatile Nutrient and Hormone Essential for Health

Vitamin D, a unique compound in the realm of human health, can be classified either as a vitamin or a hormone. Its active form, calcitriol, functions similarly to a hormone because it is synthesized in one part of the body and exerts regulatory effects on distant tissues.

A crucial role of vitamin D is its regulation of calcium and phosphorus absorption in the digestive tract, facilitating their deposition in bones. This process is vital for the formation and maintenance of strong bones. When dietary calcium is insufficient, vitamin D mobilizes calcium from skeletal reserves to meet the body's needs. This interaction is part of a complex regulatory system involving parathyroid hormone (PTH) from the parathyroid glands and calcitonin from the thyroid glands.

In addition to its skeletal functions, vitamin D influences cell differentiation and growth. It modulates the transcription of cell cycle proteins, reducing cell proliferation and enhancing differentiation in various cell types, including osteoclastic precursors (bone-resorbing cells), enterocytes (intestinal lining cells), and keratinocytes (skin cells). This regulatory capability has implications for cancer prevention, notably colorectal cancer, where adequate vitamin D levels may offer protective benefits.

Moreover, vitamin D plays a significant role in immune defense. It is found in high concentrations in T-lymphocytes, critical cells in the immune system. Emerging research suggests that adequate vitamin D levels in early life might prevent the onset of autoimmune diseases such as type 1 diabetes by modulating immune responses.

Vitamin D synthesis begins in the skin, where 7-dehydrocholesterol is converted to cholecalciferol upon exposure to sunlight. Cholecalciferol then enters the bloodstream and travels to the liver for further conversion to its active form. This fat-soluble steroid hormone precursor is essential for maintaining normal calcium and phosphorus levels in the blood, which are critical for bone mineralization, muscle contraction, nerve conduction, and overall cellular function.

Recent studies underscore the broader health implications of vitamin D. Its deficiency has been linked to various disorders, including osteoporosis, cardiovascular diseases, and certain infections. Ensuring adequate vitamin D levels through sunlight exposure, diet, or supplementation is crucial for maintaining overall health and preventing a spectrum of diseases. As research progresses, the understanding of vitamin D's multifaceted roles continues to expand, highlighting its importance as both a nutrient and a regulatory hormone in human physiology.
Vitamin D: The Versatile Nutrient and Hormone Essential for Health

Morning Market Fish: Rich in Vitamin D

Vitamin D (D3 and D2)

Vitamin D is required for calcium and phosphorus absorption, normal mineralization of bone, and mobilization of calcium from bone. This vitamin has been called the sunshine vitamin since ultraviolet light is involved in the conversion of provitamin substances to vitamins D2 and D3.

Vitamin D is the general name given to a group of fat-soluble compounds that are essential for maintaining the mineral balance in the body.

The main forms are vitamin D2 and vitamin D3. In nature only a few foods contain vitamin D, such as fatty fish, liver and egg yolks.

Vitamin D is a generic term of all steroids including vitamin D3 and vitamin D2. Vitamin D3, also known as cholecalciferol, and D2, known as ergocalciferol.

Vitamin D3, is the primary form of the vitamin encountered in zoologic species; it is stored in a number of tissues, including the liver and skin. Fish liver oils are a rich natural source of this material.

Vitamin D3, produced in the skin of humans and animals by the action of sunlight (ultraviolet light 290 to 320 nm) on its precursor molecule, the cholesterol derivative 7-dehydrocholesterol (a normal metabolite of cholesterol found in the skin). Absorption of light energy induces breakage of the 9, 10 carbon bond; a spontaneous isomerization (shifting of double bonds) then occurs. It is said to be more bioactive.

Ergocalciferol, or vitamin D2, is derived from ergosterol, a plant steroid and only enters the body via the diet, from consumption of foods such as oily fish, egg yolk and liver. It is the form of this vitamin normally used to fortify such foods as milk, bread, and cereals.

Vitamin D is absorbed from the diet in the intestinal tract in association with liquids and the presence of the bile slats. Once in the liver, one metabolite 25 hydroxy-vitamin D3 is formed, which is a about four times as active as vitamin D.

Vitamin D (D3 and D2) in physiologic replacement and pharmacologic doses has been used to correct vitamin D depletion in the elderly and to prevent vitamin D deficiency at all ages.
Vitamin D (D3 and D2)

Food sources of Vitamin D

Vitamin D is a fat-soluble vitamin that has long been known to help the body absorb and retain calcium and phosphorus; both are critical for building bone.

Few foods naturally contain vitamin D, though some foods are fortified with the vitamin. Fortified forms are included in milk, cereals, and some margarines. The chief food sources of vitamin D in western diets are fortified milk and cereals, and fatty fish. Cereals are considered the best breakfast supported with essential vitamins and nutrients, including vitamin D, in reasonable amounts. For most people, the best way to get enough vitamin D is taking a supplement because it is hard to eat enough through food.

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.

Natural sources include fish oils, salmon, sardines, herring, liver, and egg yolks. Egg yolk contains 18 IU of vitamin D. Cheese is among the best foods high in Vitamin D. It is valued for its high content of phosphorus, fat, protein, vitamins, and calcium.

Two basic substances with vitamin D activity, D2 and D3, occur only in yeast and fish liver oils. A fish can naturally store vitamin D in its liver and fat tissues. Sardines, mackerel, trout are some fish that are food with vitamin D.

Salmon is a popular fatty fish and a great source of vitamin D. According to the United States Department of Agriculture (USDA) Food Composition Database, one 3.5-ounce (100-gram) serving of farmed Atlantic salmon contains 526 IU of vitamin D, or 66% of the DV

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.

The daily value (DV) for vitamin D is 800 IU (20 mcg). The vitamin D content is listed as a percentage of the DV on the nutrition facts label on food packages.
Food sources of Vitamin D

Diseases associated with Vitamin D deficiency

Vitamin D deficiency is the true epidemic of the times. It is perhaps more common than any other medical condition at the present time. Symptoms of vitamin D deficiency can include muscle weakness, pain, fatigue and depression.

Vitamin D is one of many vitamins human bodies need to stay healthy. Traditionally, vitamin D deficiency has been associated with rickets (deformities of bone, such as bow legs and curvature of the spine) and teeth defects. It can cause osteomalacia in adults.

Vitamin D plays important roles in immune function. One of the most common symptoms of a deficiency is an increased risk of illness or infections.

Deficient of vitamin D levels resulting reduced calcium absorption, to only 10 to 15 percent of dietary calcium, and less than 50 percent absorption of dietary phosphorus. As a result, the protein scaffold made by osteoblasts can’t be mineralized. Vitamin D, along with calcium, helps build bones and keep bones strong and healthy. Weak bones can lead to osteoporosis, the loss of bone density, which can lead to fractures.

With chronic and/or severe vitamin D deficiency, a decline in intestinal calcium and phosphorus absorption leads to hypocalcemia leading to secondary hyperparathyroidism.

There was a hypothesis that vitamin D deficiency may increase the risk of prostate cancer, based on the finding that mortality rates of this cancer in the United States were inversely proportional to ultraviolet radiation.

Several studies have shown a link between a deficiency and respiratory tract infections such as colds, bronchitis, and pneumonia.

Scientist also are looking for ways vitamin D and its derivatives might treat other conditions of abnormal cell growth, such as psoriasis and cancers of the blood, lung and cervix.

Vitamin D deficiency has been linked to increased risk for cardiovascular disease, multiple sclerosis, rheumatoid arthritis and type 1 diabetes.
Diseases associated with Vitamin D deficiency

Salmon - rich source with Vitamin D

Symptoms of vitamin D deficiency

The major source of vitamin D for humans is exposure to sunlight. Anything that diminishes the transmission of solar UVB radiation to the earth’s surface or anything that interferes with the penetration of UVB radiation into the skin will affect the cutaneous synthesis of vitamin D3.

Very few foods naturally contain vitamin D, and foods that are fortified with vitamin D are often inadequate to satisfy either a child’s or an adult’s vitamin D requirement.

Symptoms that point to vitamin D deficiency are muscle spasms, bone pain and joint pain. Lesser degrees of deficiency may be characterized by loss of appetite, a burning sensation in the mouth and throat, diarrhea, insomnia, visual problems, and weight loss.

Vitamin D deficiency causes bone to demineralize. In children, vitamin D deficiency causes rickets, a disease in which the bones become soft, weak, deformed, and painful.

Adults with osteomalacia may experience global bone discomfort and muscle aches, often leading to a misdiagnosis of fibromyalgia, chronic fatigue syndrome, or arthritis.

Long-term shortages of vitamin D and calcium cause human bones to become fragile and break more easily. This condition is called osteoporosis.
Symptoms of vitamin D deficiency

Vitamin D from natural sources

Very few naturally occurring foods are rich in vitamin D. Typically animal foods contain cholecalciferol, while plant foods contain ergocalciferol. Some food items that naturally contain small amounts of vitamin D include oil fish such as salmon, mackerel and blue fish. Cod liver oil is the best source of vitamin D.

Liver meat is another source of abundant vitamin D. For vegetarians or vegans, all edible mushrooms have some content of vitamin D2 and ergosterol, which becomes activated with UVB exposure.

The two basic substances with vitamin D activity D2 and D3, occur only in yeast and fish liver oils. Vitamin D is also presents in small quantities in vegetables, meat and egg yolk.

The main food sources are those to which crystalline vitamin D has been added. Milk, because it is commonly used, has proved to be the most practical carrier. In United States fluid milk is voluntary fortified with 400 IU per quart of vitamin D.

The most efficient source of the vitamin D is not a food at all, but exposure to sunlight, which transforms a related pro-vitamin substance in the skin into a substance which the kidney can change into active vitamin D.

Sunlight provides 90 to 100% of the requirement for most people who are exposed to adequate sunlight. Vitamin D3 is synthesized in human skin from 7-dehydrocholesterol following exposure to ultraviolet B radiation with wavelength 290 to 320 nm.

Like other fat soluble vitamins, the sunlight activated pro-vitamin D can be stored away in the liver.
Vitamin D from natural sources

Rickets due to vitamin D deficiency

Vitamin D has two sources, the sun and diet, and the relative importance of the two depends on location, season and individual attributes.

Rickets is caused by inadequate exposure to sunlight or dietary lack of vitamin D and occurs in childhood. It is characterized by rapidly growing bones grow soft and eventually bend under the weight of the body due to poor of calcium and phosphorus deposition.

Vitamin D also essential for normal development and maintenance of muscles and in rickets the muscles are greatly weakened, tender and sore.

It’s a defect in the mineralization of bone matrix with increase bone mass. Weight-bearing bones buckle, the head becomes malformed, wrists and ankles become enlarged and the sternum bows to resemble a pigeon breast.

If the rickets develop in the first 6 months of life, infants may suffer from convulsions or develop tetany, but have only minor skeletal changes; however, after 6 months, bone abnormalities, pain as well as tetany, are likely to be present.
Rickets due to vitamin D deficiency

Synthesis of vitamin D in the skin

The human body also is able to synthesize this vitamin from components of the skin through exposure to ultraviolet or sunlight. Most of the world’s population relies on natural exposure to sunlight to maintain adequate vitamin D nutrition.

To get all vitamins D is to go outside. That’s because vitamin D is made when the sun shines on the human skin.

In the skin, 7-dehydrocholesterol in the epidermis and dermis changes conformation ultraviolet B (UVB) radiation in the wavelength range of 280-315 nm passes through these skin layers to form pre-vitamin D3.

Subsequent enzymic conversion occurs outside the skin predominantly, although both the necessary enzymes, 25-hydroxylase and 1 α-hydroxylase are present in the skin.  Thus the active form of vitamin D,1,25-dihydroxyvitamin D3 may be present in the skin.

While the reaction to form pre-vitamin D3 takes minutes, the reaction converting it to vitamin D3 takes hours to occur and is a rate-limiting step.

The vitamin D3 gets carried to liver, where it gets changes into a more active form; from there, it goes to kidneys, where it becomes even more active.

Some of the vitamin D3 stays in liver and kidneys, where it helps reabsorb calcium from blood.
Synthesis of vitamin D in the skin

Compound of vitamin D: cholecalciferol and ergocalciferol

There are ten compounds of vitamin D, called vitamin D1 through vitamin D10. The most important of these compounds are D2 (ergocalciferol) and D3 (cholecalciferol).

Ergocalciferol is found exclusively on plant foods. It is formed from plant sterol ergosterol by the action of UV light.

Cholecalciferol is found in animal foods such as eggs and fish oils, most is synthesized in the skin. Cholecalciferol is formed directly from the steroid known as 7-dehydrocholesterol by the action of sunlight, or other source of ultraviolet light.

Cholecalciferol and ergocalciferol in the diet are absorbed and carried to the liver in chylomicrons. 

Cholecalciferol and ergocalciferol circulated for only 1 or 2 days. This quick turnover is due to rapid hepatic conversion and uptake by fat and muscle cells.

In the liver, cholecalciferol and ergocalciferol are converted in to calcidiol and then sent to the kidneys. Calcidiol is the main circulating form of the vitamin.

The kidneys perform the final step – the formation of 1,25-dihydroxyvitamin D3 which is also called calcitriol.

1,25-dihydroxyvitamin D3 is the active form of vitamin D, and the body derives about 90 percent of its 1,25-dihydroxyvitamin D3 from the cholecalciferol synthesized in the skin.
Compound of vitamin D: cholecalciferol and ergocalciferol

Vitamin D deficiency increases risk of cardiovascular disease

Many studies suggest that vitamin D may play a significant role in many aspects of heart and vascular health. 

In one study published in January 2008 in Circulation, researchers followed 1739 participants for the development of heart disease. The study analyzed data on 1739 men and women (average age, 59) without cardiovascular disease. About 40% had high blood pressure.

In a five year period, 120 people had a cardiovascular event, which may have included the new onset of cardiac chest pain, heart attacks, heart failure, strokes, and leg pain due to inadequate blood supply.

Based on blood tests, people moderately deficient in vitamin D were 62% more likely to have had heart trouble than were those with higher vitamin D levels.

The patients who had high blood pressure with the lowest levels of vitamin D had twice as many serious cardiovascular events compared to these with high blood pressure and the highest blood levels of vitamin D. 

Another study published in June 9, 2008 in Archives of Internal Medicine, researchers found at the level of vitamin D in men who developed a heart attack during a 10 year follow-up period.

The result was the lower the vitamin D level, the higher the risk for heart attack.

Food sources of vitamin D include milk, fortified cereal, salmon, mackerel, sardines, and tuna, Sunshine is another source.

The researchers found that vitamin D was able to prevent the uptake of LDL cholesterol by the cells in the arterial walls, which is the main reason for narrowing of the coronary arteries.

Vitamin D deficiency is common among patients with myocardial diseases because sun-induced vitamin D production in the skin and dietary intake of vitamin D is often insufficient.
Vitamin D deficiency increases risk of cardiovascular disease

The definition of osteoporosis

The literal meaning of osteoporosis is ‘porous’. Osteoporosis is a preventable, treatable condition of weak, hollow, brittle bones that break easily.

Osteoporosis is one of the most common disorders to be found in elderly populations.

Bone is a specialized form of mineralized connective tissue that is build by various types of metabolically active cells during embryonic and postnatal development.

Bones are living tissues. Throughout life, old bone is removed and replaced by new bone.

If old bone is removed at a rate that is too fast, or if the rate of new bone replacement occurs too slowly, then gradually bones become porous and fragile. For example, 40% of the bone's density can be lost during advanced osteoporosis.

In general, it is a systematic disease where rigidity and mechanical stability of bone declines, until bone loses the ability to withstand function loading or weak traumata.

A lifelong adequate intake of calcium and vitamin D, as well as phosphorus, zinc, vitamins K and C, copper and manganese, helps bone health by increasing the amount of bone formed during youth and early adulthood.

Adequate diet and hormone levels also slow down the rate of overall bone loss that occurs later in life.

When recommended amounts of calcium are consumed during the bone-building years, maximum bone mass "reserves" with a consequent reduction in osteoporosis, and 50% fewer hip fractures later in life. 

Osteoporosis is second only to cardiovascular disease as a leading health care problem worldwide. The WHO estimates that one on three women and one in eight men over age 50 risk having osteoporotic fracture during their lifetime.

In its advanced stages, a painful condition affecting approximately 30 million Americans, causing fractures, typically of the hip, wrist, and spine.
The definition of osteoporosis

The importance of vitamin D

Vitamin D is represented by cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2), which are structurally similar secosteroids derived from the UV irradiation of vitamin D sterols.

Vitamin D (calciferol or activated ergosterol) is fat soluble. This vitamin is necessary for normal tooth and bone formation.

Growing evidence indicates that vitamin D is also involved in modulating body composition, energy homeostasis, insulin sensitivity and immune function.

Deficiencies in vitamin D result in rickets (deformities of bones, such as bow-legs and curvature of the spine) and teeth defects.

Vitamin D has been observed to be associated with broadening fields of health problems including cardiovascular disease and diabetes mellitus. New research says that vitamin D helps to prevent cancer.

The human body also able to synthesize this vitamin form components of the skin exposure to ultraviolet light or sunlight. Exposure to the sun without sun screen for 30 minutes can synthesize approximately 10,000 to 20,000 IU of vitamin D in the skin.

Vitamin D is routinely added to milk. The richest natural sources of vitamin D3 are fish liver oils, especially halibut-liver oil.

Fatty fish, such as herring, sardines, pilchards and tune, are rich natural food sources; smaller amounts of the vitamin are found in mammalian liver, eggs, and diary products.
The importance of vitamin D

Vitamin D deficiency

Vitamin D deficiency is a common problem or many people especially the older people. Vitamin D is a critical nutrient for human body in particular for stronger bones, muscle movements, nerve function and immune system well-being.

Severe deficiency of vitamin D can cause rickets in children and osteomalacia, a similar disorder, in adults. 

This due to deficient vitamin D levels resulting reduced calcium absorption, to only 10 to 15 percent of dietary calcium, and less than 50 percent absorption of dietary phosphorus. As a result, the protein scaffold made by osteoblasts can’t be mineralized.

Lesser degrees of deficiency may be characterized by loss of appetite, a burning sensation in the mouth and throat, diarrhea, insomnia, visual problems and weight loss.

There was a hypothesis that vitamin D deficiency may increase the risk of prostate cancer, based on the finding that mortality rates of this cancer in the United States were inversely proportional to ultraviolet radiation.

Vitamin D deficiency has been linked to increased risk for cardiovascular disease, multiple sclerosis, rheumatoid arthritis and type 1 diabetes.

Symptoms that point to vitamin D deficiency are muscle spasms, bone pain and joint pain. Vitamin D deficiency can arise from lack of sunlight exposure lack of dietary vitamin D intake or impaired intestinal absorption of the vitamin.

Among other the causes of vitamin D deficiency included:
*Modern lifestyle
*Sun Phobia
*Obesity
*Medical illness
*Medications
Vitamin D deficiency

Vitamin D natural sources

Diet is not a major source of vitamin D. Perfectly reasonably and well balanced diet may not supply the amount required to prevent deficiency.

Only a few food sources naturally contain appreciable sources of vitamin D3 that have an impact on dietary intake: fish, fish liver, fish liver oil, fatty fish, mushroom, egg yolks and beef liver.

Cod liver oil is the best source of vitamin D. Salmon contains a fair amount of vitamin D; 3 ounces of salmon had about 800 IU of vitamin D. Fatty fish represents the richest natural sources of vitamin D commonly consumed in North America.

Vitamin D is also presents in small quantities in vegetables, meat and egg yolk. Mushrooms are the only vegan source of vitamin D. This form is vitamin D2.

The main food sources are those to which crystalline vitamin D has been added. Milk, because it is commonly used, has proved to be the most practical carrier. Milk, whether nonfat, reduced fat, or whole, provides about 100 IU of vitamin D per ounce glass, and that’s after it has been fortified with vitamin D.

The most efficient source of the vitamin is not a food at all, but exposure to sunlight, which transforms a related pro-vitamin substance in the skin into a substance which the kidney can change into active vitamin D. 

The sun is the major source of vitamin D. Sunlight, in the form of ultraviolet-B radiation, providing 90-100% of the requirement for most of the people who are exposed to adequate sunlight.
Vitamin D natural sources

Vitamin D and diabetes

The role of vitamin D as an anti-inflammatory has taken center stage in age-related diseases such as cardiovascular diseases, adult onset diabetes, depression and dementia.

There was a study in Netherlands shows that the lower the vitamin D level, the greater the intolerance to glucose.

In the August 2009 issue of Pediatrics, researchers noted a significant link between vitamin D levels and blood sugars in adolescents. Vitamin D deficiency has been long suspected of being a risk for type I diabetes in the basis of indirect evidence that countries at higher latitudes report higher incidence and prevalence rates of type I diabetes compared with countries at lower latitudes.

In animal studies by the University of California at Riverside showed that vitamin D is necessary for the pancreas to release insulin. Active vitamin D binding to its receptor located in pancreatic islet cells is thought to promote insulin secretion. Vitamin D deficiency produces insulin resistance in tissues.

Vitamin D actually directly acts on the muscle and fat cells to improve insulin action by reducing insulin resistance. Vitamin D directly improves insulin production and its action by improving the level of calcium inside the cells.

Vitamin D deficiency has been shown to impair insulin synthesis and secretion in humans and in animal model of diabetes. This vitamin needed to maintain adequate blood levels of insulin. Actually levels of vitamin D are associated with control of many things that cause complications in diabetes: higher levels of HDL-C, lower levels of LDL-C, and better blood pressure control.

A 2007 study published in Diabetes care concluded that vitamin D can reduce risk of developing type 2 diabetes by up to 40 percent. Vitamin D would appear to have a potential role in the prevention of diabetes and the metabolic syndrome.
Vitamin D and diabetes

Vitamin D Deficiency

Vitamin D deficiency is a relatively new phenomenon. Scientists first recognized it in the 17th century in the UK and other Northern European countries.

Vitamin D is a critical nutrient for human body in particular for stronger bones, muscle movements, nerve function and immune system well – being. Human skin evolved to create vitamin D when it's exposed to the sun's ultraviolet (UV) rays.

Vitamin D deficiency results from inadequate dietary intake of preformed vitamin D, malabsorption of vitamin D, or too little exposure to sunlight.

More recently, justifiable concerns about sunburns and skin cancer have prompted increasing shares of people—even at high latitudes—to do sun-blocking clothing. Unfortunately, what's good for skin protection is bad for natural vitamin D production.

Another main reason is human modern life style, which minimizes exposure to the sun, Technological revolution has dramatically changed lifestyles around the globe where most people work indoors. Even at lunch, most people drive to a restaurant or stay inside to eat.

Because of vitamin D is fat soluble vitamin, nutritional osteomalacia usually is associated with a deficient intake of food products containing fatty substances.

More studies are linking the symptom associated with many disease of civilization with vitamin D deficiency.
-Muscular weakness
-Feeling of heaviness in the legs
-Chronic musculoskeletal pain
-Fatigue or easy tiring
-Frequent infections
-Depression

The deficiency results in rickets in infants and young children and osteomalacia in adults. Adults, ages 19 to 70, require 600 IU (International Units) of Vitamin D per day. Adults ages 71 and above, require 800 IU per day.
Vitamin D Deficiency