Fat-Soluble Vitamins A,D,E,K in detail

Vitamin A

Vitamin A: We consume significant amounts of vitamin A in an inactive form. Stored primarily in the liver, vitamin A encompasses a group of fat-soluble compounds composed of retinoids and several carotenoids. Retinoid compounds are retinal, retinol, and retinoic acid. Retinol is also referred to as preformed vitamin A because it is already in an active form in foods. Though retinol is the only retinoid present in significant amounts in our diet, once it is absorbed we can readily (and reversibly) convert it to retinal, and a small amount of retinal is irreversibly converted to retinoic acid. In contrast, compounds that have vitamin activity only after conversion to active forms are provitamins. For example, provitamin A carotenoids are compounds (primarily beta-carotene) that have vitamin A activity once they are converted in the body into one of the active forms of the vitamin (retinol, retinal, or retinoic acid). Functions: Vision and cell differentiation, functions as a hormone. Cell Development. Vitamin A serves many critical biochemical and physiological functions in the body related to vision, cell development, immune function, and growth. Along with these important functions, vitamin A also plays key roles in bone health and reproduction, such as sperm and fetal development. Except for its role in vision, vitamin A almost always functions as a hormone that exerts its effects by controlling the synthesis of numerous proteins encoded in our genes. The hormonal actions of vitamin A play a key role in normal, healthy cell development, such as in cell differentiation. Vitamin A is particularly important to epithelial cells. It also plays a role in the development of immune cells, which affects how well our immune system functions and, therefore, influences our susceptibility to disease. In addition, vitamin A is required by our eyes to convert light into nerve impulses that bring messages to the brain, telling us what we're seeing. Specifically, vitamin A is a key component of rhodopsin, the visual pigment that is formed when retinal binds to the protein opsin. Rhodopsin is found in light-sensing cells within the retina at the back of the eye. When rhodopsin absorbs light, retinal changes its shape and is then released, triggering a chain of events that generate a nerve impulse that transmits the visual signal to the brain. When the vitamin A level is low, these light-sensing cells are unable to quickly regenerate rhodopsin, which can make it difficult to see in low light. We also need vitamin A to maintain the health of the cornea, the clear outer covering at the front of the eye. The plant form of vitamin A—beta-carotene—as well as the other dietary carotenoids have important roles as health-promoting phytochemicals. Foods: In the United States, approximately two-thirds of the vitamin A is consumed as preformed vitamin A (retinol) from fortified foods, and supplements, and foods that naturally contain retinol. For example, preformed vitamin A occurs in animal products; it is highest in liver, but fish, eggs, and dairy foods (containing fat) are also good sources. In the United States and Canada, reduced-fat milk and yogurt must be fortified with vitamin A to make up for the loss of this vitamin during the removal of the fat. The rest of our vitamin A comes from provitamin A carotenoids, which must be converted into an active form in the body before they can fulfill biological functions. These compounds are the yellow, orange, and red pigments of fruits and vegetables—think sweet potatoes, carrots, cantaloupe, and apricots, as well as dark, leafy greens (which, despite their color, contain a lot of beta-carotene). Although more than 700 carotenoids have been identified, about 50 are present in commonly consumed foods, and of the approximately 12 carotenoids that have been identified in blood and tissues, only three are converted in significant amounts to active vitamin A—with beta-carotene being by far the most abundant. *Beef Liver (braised) 8,026mcg *Sweet Potatoes (boiled) 1,291mcg *Braunschweiger (liver sausage) 1,196mcg *Bluefin Tuna fresh (cooked) 643 *Butternut squash (cooked) 572mcg *Baby carrots (raw) 442mcg *Cheddar cheese (diced) 350mcg *Post, Cranberry Almond Crunch 224mcg *Romaine lettuce (raw, shredded) 205mcg *Skim milk (fortified) 149mcg *Spinach (raw) 141mcg *Cantaloupe 135mcg *Bell Peppers (sweet red raw) 117 *Whole Milk (unfortified) 112mcg *Apricots 79mcg *Grapefruit pink and red sections 67mcg *Prunes 58mcg *Coho salmon (cooked) 50mcg *Mango 45mcg *Peaches (slices) 12mcg Vitamin A Bioavailability and Recommendations: The bioavailability of vitamin A differs upon the food source. Preformed vitamin A (retinol), found in foods from animal sources, is more easily absorbed than the carotenoids found in foods from plant sources. To account for these differences in bioavailability, the Dietary Reference Intake (DRI) values are expressed as micrograms (mcg; one millionth of a gram) of retinol activity equivalents, or RAE. The RDA for vitamin A for men aged 19 to 50 years is thus 900 mcg RAE; for women of the same age, it is 700 mcg RAE. Of the provitamin A carotenoids, beta-carotene is best converted into retinol, but this conversion is never complete. Even when beta-carotene is consumed as a supplement in oil (to improve absorption), it takes two micrograms of beta-carotene to provide the equivalent of one microgram of retinol. Because the absorption of carotenoids from foods is even poorer than from supplements, you need to eat 12 micrograms of dietary beta-carotene to reach the equivalent RAE of only one microgram of retinol. Because the release of carotenoids from food is difficult, processing the food by slicing, chopping, and even juicing can improve their bioavailability. The smaller food particles are more completely broken down by mechanical digestion than are larger particles, allowing nutrients to disperse more readily into digestive fluids. Cooking can also often increase nutrient bioavailability because it ruptures plant cells, releasing the nutrients that otherwise might be trapped within those cells and subsequently excreted. Thus, the potential vitamin A is actually higher from sliced and cooked carrots than from raw carrots. RDA Men: 900mcg RDA Women: 700mcg Deficiencies: It is estimated that about 40% of individuals living in the United States consume less than the RDA of vitamin A. In developing countries, a child's vitamin A deficiency significantly increases his or her risk of death from an infectious disease. Vitamin A deficiency delays the reformation of cis-retinal-containing Rhodopsin and night vision is slower to recover after exposure to a bright light. Although uncommon in the United States, people in developing countries develop hypovitaminosis A if they have little access to preformed vitamin A and beta-carotene. (Even in the United States, nutrition surveys suggest that most of us could benefit from higher intake closer to the DRI.) The hallmark symptoms of vitamin A deficiency affect the eye. Night blindness occurs first, the result of problems in the synthesis of rhodopsin. The changes in protein synthesis resulting from a deficiency of vitamin A decrease the production of mucous in tears, and then the cornea of the eye begins to dry and thicken. If the deficiency continues, ulcers form on the cornea and this can lead to scarring—-resulting in permanent blindness. In fact, vitamin A deficiency is the leading cause of preventable blindness in children worldwide. Other symptoms include impaired immunity (increasing the risk of infections), and rough, dry, or scaly skin, resulting from a loss of moisture in the mucous membranes. This last symptom—known as keratinization—occurs as the epithelial cells that cover the surface of our bodies (like the cornea of the eye) and line body cavities cannot develop properly; as a consequence they become filled with a fibrous structural protein called keratin. These are the same type of proteins that make up our nails, hair, and even the horns of animals. Over-consumption: When people consume too much vitamin A they develop hypervitaminosis A, which mostly occurs after taking supplements of large quantities of vitamin A. Here, the risks are largely defects or weaknesses in bones, leading to osteoporosis or fractures. The UL for vitamin A for adults 19 years and older is set at 3,000 mcg RAE. In pregnant women, high amounts of vitamin A can affect fetal development and cause birth defects. But these problems can result from too much vitamin A from animal foods or from dietary supplements—excess beta-carotene from plant sources does not cause toxicity, but may temporarily turn your skin yellow or orange color in color, called Carotenemia (elevated blood levels of carotene caused by excessive consumption of foods such as carrots, squash, and sweet potatoes).

Vitamin D

Vitamin D: often called the "sunshine vitamin," since it can be produced in the skin from cholesterol with exposure to ultraviolet (UV) light. Most of us meet at least some of our vitamin D needs this way, but with limited sun exposure or impaired synthesis it becomes important to consume sufficient vitamin D through our diet. But, whether through synthesis in the skin or through foods, vitamin D must be activated in the kidneys and liver to fulfill its biological functions in the body. Vitamin D is converted into its fully active hormone form (Calcitriol) in the kidneys. Functions: Bone growth and maintenance, cell development, and immunity, functions as a hormone. Vitamin D plays a key role in the growth and maintenance of bone by maintaining blood concentrations of minerals involved in bone development, such as calcium and phosphorus. In addition, vitamin D works in combination with other nutrients and hormones in bone growth and maintenance. Vitamin D actually functions as a hormone, since, like hormones, it is made in one part of the body, but carries out its regulatory effects elsewhere. Since it is made from cholesterol, vitamin D is a member of the steroid family of hormones (which includes estrogen, testosterone, and cortisol, among others). It is estimated that calcitriol is involved in regulating the synthesis of 5% of all proteins in the body. Consequently, it is required for normal cell development and immune function and is critical for other organs and body systems, including the brain, heart, and nervous system, reproductive organs, skin, and muscle. Recent findings suggest that maintaining vitamin D levels in the elderly increases muscle strength and function, and appears to reduce the risk of falls. Evidence is also accumulating that vitamin D is necessary for regulating cardiovascular function. Research now provides evidence that sufficient intake and stores of vitamin D may reduce the risk of a number of important diseases, including cancer, autoimmune diseases, kidney disease, type 2 diabetes, and even cardiovascular disease. Vitamin D also plays an important role in the regulation of calcium. Most calcium in the body is stored in bones with less than 1% circulating in the blood; however, this circulating calcium is critical for normal muscle and nerve functioning and must be maintained. Vitamin D must be metabolized to its active form by the liver and kidneys. Vitamin D helps maintain Calcium concentrations in the blood: The effects of active vitamin D on the kidneys and bone require the cooperative action of parathyroid hormone. When calcium concentrations in blood decrease, more of vitamin D is converted into the active hormonal form, which will increase blood calcium by acting on bone, the small intestine, and the kidneys. *low blood calcium levels *parathyroid hormone is released from the parathyroid glands in response to low blood calcium levels, stimulating the kidneys to increase the production of active vitamin D *kidney- active vitamin D increases calcium uptake from urine. Activated vitamin D also works together with parathyroid hormone to decrease calcium excretion by the kidneys, and increase its release from bone to raise blood calcium concentrations. *bone- active vitamin D increases calcium release from bone *intestine- activated vitamin D increases absorption of calcium from the intestines. This active hormonal form of vitamin D then increases the absorption of calcium in the gastrointestinal tract—for this reason, you will often find calcium supplements that also contain vitamin D. Vitamin D Activation and Calcium Maintenance in the Blood: Vitamin D functions as a hormone to regulate calcium metabolism. Together with parathyroid hormone, vitamin D tightly controls blood (serum) concentrations of calcium. Vitamin D Activation: *Inactive Vitamin D is synthesized by the skin. Inactive is consumed in the diet. *Inactive vitamin D enters circulation and is transported to the liver. *Conversion to the active form of vitamin D begins in the liver *The active hormonal form of vitamin D is produced in the kidneys Foods: vitamin D is present in very few foods naturally. Best dietary sources: vitamin D—fortified foods and fish. Some of the best sources include fatty fish (such as salmon, tuna, and mackerel) and fish liver oils. Beef liver, cheese, eggs, and some mushrooms (particularly those exposed to UV light) contain small amounts of vitamin D. Alternatively, most Americans get dietary vitamin D from fortified foods—most of the U.S. milk supply is fortified with vitamin D (100 IU, or 2.5 mcg, per cup). This is the result of a milk fortification program that was instituted in the 1930s in the United States to reduce the incidence of rickets, a significant public health issue at the time.Vitamin D does not occur naturally in many foods besides fish; the most common sources in the U.S. diet are fortified foods. *Cod Liver Oil 34mcg *Rainbow Trout (farmed, cooked dry heat) 16.2mcg *Chinook Salmon (smoked) 14.5mcg *Maitake Mushrooms (raw) 9.8mcg *American Cheese (fortified) 5.2mcg *Atlantic Sardines (canned in oil, drained) 4.1mcg *Skim Milk (fortified) 2.9mcg *Orange Juice (fortified) = General Mills Total Raisin Bran 2.5mcg *Tuna Fish (white, canned in water) = Morel Mushrooms (raw) 1.7mcg *Hard Boiled Egg (1 lg) 1.1mcg *Butter = Whole Milk 0.2mcg Those at Risk for Vitamin D Deficiency: Vitamin D is listed as a nutrient of concern in the 2010 Dietary Guidelines for Americans. Although 80% of Americans are reported to receive enough of the nutrient, according to data from the 2001-2006 National Health and Nutrition Examination Survey, about 8% of Americans were at risk for vitamin D deficiency. People most at risk are those who avoid vitamin D-fortified dairy products (because of allergies, intolerance, or a vegan diet); people with dark skin (since the melanin that darkens skin can interfere with the body's ability to make vitamin D from sunlight); and those with little sun exposure, or who regularly use sunscreen. Although sunscreen can block UV rays and reduce the risk of skin cancer, it also prevents vitamin D synthesis. Other groups at risk include infants who are exclusively breast-fed, since breast milk is not a rich source of vitamin D, and the elderly, who have a reduced ability to synthesize vitamin D when exposed to sunlight. Many elderly individuals are also more likely to stay indoors and therefore have less opportunity to synthesize vitamin D. Deficiencies: In humans, rickets affects bone development in children usually because of an extreme vitamin D and calcium deficiency. Having extremely low levels of vitamin D can, over time, cause serious bone diseases. Starting in the mid-1600s, researchers began describing mysterious symptoms in children that Holick instantly recognized in Kimani— "bowed" legs, soft bones, and other skeletal malformations. Today we know that rickets is caused by low vitamin D levels, leading to impairments in the maturation and mineralization of cartilage in regions of the bone where growth is occurring, causing the characteristic "bowed" legs or "knocked" knees. In adults, the same deficiency can cause osteomalacia, in which the bone mineral is being depleted, causing the bones to become soft or weak and putting people at risk of fractures or falls, as well as creating pain in the pelvis, lower back, and legs. Over-consumption: too much vitamin D—called hypervitaminosis D—which is likely the result of supplement use rather than food intake or sun exposure. The established UL for vitamin D is set at 4,000 IU (100 mcg) for males and females 9 years and older. The symptoms of hypervitaminosis D vary, but may include loss of appetite, weight loss, irregular heartbeat, and frequent urination. Having too much vitamin D can also increase levels of calcium in the blood, which leads to calcification of the soft tissue and damage to the heart, blood vessels, and the formation of kidney stones. Recommendations: 15 mcg for both Male and Female. Although sunlight can be a significant source of vitamin D, the RDAs—established to maintain bone health and normal calcium metabolism in healthy people—are set on the basis of minimal sun exposure. In 2010, the Institute of Medicine increased the RDA for vitamin D for all age groups—it was increased threefold to 600 IU (15 mcg), for example, for adults in the 19 to 50 years age range. However, the recent appreciation of the importance of vitamin D for functions beyond that of bone health has caused some scientists to question whether the new RDAs are actually high enough to provide for optimal health.

Vitamin E

Vitamin E: Vitamin E encompasses a group of fat-soluble compounds found primarily in vegetable oils. The compounds are known as tocopherols. Only alpha-tocopherol supplements have been shown to reverse vitamin E deficiency symptoms in humans. For this reason, it is the only form defined by the Food and Nutrition Board of the Institute of Medicine as meeting human vitamin E requirements. Vitamin E has no regulatory function Functions: Antioxidant. Because of its unique ability to effectively be incorporated into cell membranes, vitamin E acts within membranes as an antioxidant, protecting cells throughout the body from the oxidative damage that results from exposure to free radicals produced in the body or present in the environment. It also helps prevent oxidative changes in low-density lipoproteins (LDLs) that may play a role in reducing plaque formation in blood vessels. The Antioxidant Functions of Vitamin E: Vitamin E can break the chain of oxidation by donating an electron to free radicals without becoming unstable. Because it is a fat-soluble vitamin it is particularly good at performing this function in cell membranes, and even in lipoproteins like LDL. Vitamin E appears to be of particular importance in maintaining healthy immune function by protecting white blood cells from oxidative damage, particularly in aging adults. Adequate intake of vitamin E is also necessary to prevent damage to nervous tissue. Many claims have been made about vitamin E's potential to promote health and prevent and treat disease. Despite its role as an antioxidant, rigorous studies have not produced consistent and convincing evidence that vitamin E supplements (which are almost always alpha-tocopherol) reduce the risk of cancer or heart disease. However, recent research suggests that other forms of vitamin E that are abundant in our diet may reduce our risk of cancer, cardiovascular, and neurodegenerative diseases. Foods: It is found in a variety of foods but the best sources are many nuts and some oils. Some foods (such as breakfast cereals) are fortified with vitamin E, but vitamin E is also found naturally in plant-based oils—primarily those from nuts and seeds (safflower and sunflower oils are good sources), and products made with these oils (such as margarine and salad dressings). Other natural sources include wheat germ, whole nuts and seeds, and leafy green vegetables. *Wheat Germ Oil 20.32mg *Almonds (dry roasted) 13.6mg *Meusli (dried fruits and nuts) 6.12mg *Sunflower oil 5.75mg *Trail Mix (w/ choc chips, nuts and seeds) 4.76mg *Peanut Butter 2.88mg *Canola oil 2.44mg *Avocado (raw) 2.27mg *Swordfish (cooked) 2.05mg *Olive oil 1.94mg *Blackberries (raw) 1.68mg *Jalapeno (raw, sliced) 1.61mg *Pistachios (dry roasted) 1.37mg *Kiwifruit (green, raw, sliced) 1.31mg *Margarine 1.26mg *Tomato Paste (canned) 0.69mg *Spinach (raw) 0.61mg *1 hard boiled Egg = Cashews (dry roasted) 0.52 *1 Tbsp Italian Salad Dressing: 0.32 Recommendations: The RDA for vitamin E for adults 19 years and older is 15 mg (22.4 IU). Because adverse effects have only been seen at very high levels, the UL for vitamin E (1,000 mg, or 1,500 IU) is set at more than 60 times the RDA. Deficiencies: Nutrition surveys suggest Americans may be getting less vitamin E than they should, but researchers have only rarely documented deficiency in healthy adults, so specific symptoms are unclear. vitamin E—impaired immune function Over-consumption: Vitamin E is less likely to be toxic than either vitamin A or vitamin D, and is only observed with very high intakes from supplements, which increase the tendency to bleed. Because adverse effects have only been seen at very high levels, the UL for vitamin E (1,000 mg, or 1,500 IU) is set at more than 60 times the RDA.

Vitamin K:

Vitamin K: Functions: Blood clotting and bone formation. Vitamin K is required to complete the synthesis of several proteins in blood that cause the blood to clot when those proteins are activated. The vitamin also plays a key role in bone metabolism by modifying bone proteins, which allows them to bind calcium and regulate bone formation. Although studies suggest that a diet high in vitamin K is associated with lower risk of hip fractures in aging adults, current evidence is insufficient to recommend supplementation for the prevention of osteoporosis or fractures. Foods: A significant amount of our daily requirement of vitamin K may be produced by bacteria in the intestine. The most significant dietary sources of vitamin K are green leafy vegetables (found most abundantly in green leafy vegetables); some cheeses, fruits, and vegetable oils are also good sources. *Kale (cooked) 573mcg *Spinach (cooked) 444mcg *Spinach (raw) 144.9mcg *Broccoli (cooked) 110.1mcg *Brussel Sprouts (boiled) 109.4mcg *Prunes 51.8mcg *Romaine Lettuce (raw, shredded) 48.2mcg *Asparagus (boiled) 45.5mcg *Kiwi green 36.3mcg *Cheese, Blue and Jarlsberg 30mcg *Soybean Oil 25mcg *Avocado 24.2mcg *Iceberg Lettuce 17.4mcg *Blueberries 14.3mcg *Grapes 11mcg *Canola Oil 10mcg Deficiencies: All babies are born with low levels of vitamin K. Babies generally have enough vitamin K stores to stop bleeding. However, one in 10,000 babies experience vitamin K deficiency bleeding. These babies don't have enough vitamin K to make their blood clot. For this reason, doctors recommend that all babies receive vitamin K at birth. Given its key role in blood clotting, vitamin K deficiency can cause uncontrolled bleeding, or hemorrhaging. This can result from long-term use of antibiotics that destroy intestinal bacterial, or the use of medications that prevent clotting (anti-coagulants) and interfere with the metabolism of vitamin K. Since the early 1960s, newborn babies have received a dose of vitamin K at birth to reduce the risk of hemorrhage because they have limited liver stores of vitamin K and relatively "sterile" intestines. A deficiency of vitamin K is NOT expected to affect immune function in any way Over-consumption: Toxicity is rare and there is no established UL for vitamin K, but individuals who are prescribed anti-coagulate drugs must strive to keep vitamin K intake at consistent levels from day to day as the vitamin will interfere with those medications. Recommendations: The requirements for vitamin K are given in Adequate Intake (AI) amounts since current knowledge does not provide sufficient evidence to establish a specific RDA. The AI for men 19 years and older is 120 mcg and for women in the same age range the AI is set at 90 mcg.