Fat-Soluble Vitamins (Chapter 9)

Vitamin D Toxicity

(Flynn) is not thought to be issue, even with supplementation, but the widespread use of vitamin D as a supplement is relatively new.

Vitamin E in the Diet

- Alpha-tocopherol is the form of tocopherol provides vitamin E activity as an antioxidant in humans. - Dietary sources of vitamin E include nuts, seeds, and peanuts; plant oils; leafy green vegetables; and wheat germ. Extra virgin olive oil has the highest content of alpha- tocopherol of all oils and as it is mainly monounsaturated fat, it does not oxidize so the vitamin E is available to decrease oxidation in the body. The vitamin E in vegetable oils is used to keep the oil from oxidizing. - Vitamin E is sensitive to destruction by oxygen, metals, light, and heat with some lost during food processing, cooking, and storage.

Vitamin K Toxicity and Supplements

- Because vitamin K functions in blood clotting, high doses can interfere with anticoagulant drugs, such as Coumadin. In the past, physicians restricted vitamin K containing vegetables for patients on Coumadin. Many physicians now advise that the patient consumes vitamin K containing vegetables daily and the dose of Coumadin is adjusted to the vegetable intake.

Beta-carotene functions as a Vitamin A Precursor

- Beta carotene can be converted to vitamin A in the intestinal mucosa and liver. - adequate blood carotenoid levels have been related to lowering risk of cancer and macular regeneration.

Vitamin A in the Digestive Tract

- Both preformed vitamin A and carotenoids are bound to proteins in foods, and must be released from the protein by protein-digesting enzymes to be absorbed. - Preformed vitamin A is more bioavailable than carotenoids; a lower fat content of the diet lessening the bioavailability of both. -A diet that is very low in fat (less than ) can reduce vitamin A absorption

Carotenoid Toxicity

- Carotenoids are not toxic, but a high intake can give the skin an orange appearance (hypercarotenemia). On the other hand, preformed vitamin A can be toxic (polar bear liver has high concentrations of preformed vitamin A and can cause issues with toxicity)

Meeting Vitamin K Needs with Dietary Supplements

- Currently 66% of all adult Americans consider themselves supplement users. The risk of toxicity rises with supplement use. -Eating a variety of foods is the best way to meet nutrient needs, and most healthy adults who consume a reasonably good diet do not need supplements.

How Vitamin D Functions in the Body

- Dietary Vitamin D as well as the vitamin D synthesized in the skin must be modified by the liver to form 25-hydroxy vitamin D3, and then the kidney to form active vitamin D (vitamin D: 1,25-dihydroxy vitamin D3). -When sunlight strikes the skin, a compound made from cholesterol, called 7-dehydrocholesterol, is converted to cholecalciferol (vitamin D3) (Figure 9.10). Regardless of whether the vitamin D in your body was synthesized in your skin or consumed in your diet, it is inactive until it is chemically altered in the liver and then the kidney. -The principal function of vitamin D is to maintain levels of calcium and phosphorus in the blood that favor bone mineralization. -Active vitamin D enters the blood and travels to its major target tissues—intestine, bone, and kidney—where it acts to increase calcium levels in the blood.

How Vitamin A Deficiency Affects Reproduction, Growth, and Immunity

- During reproduction, vitamin A is needed to direct cells to differentiate, forming the total organism. A lack of vitamin A during the embryonic stage results in abnormalities and death. - Poor overall growth is an early sign of vitamin A deficiency in children.

How Vitamin A Regulates Gene Expression

- In order to affect gene expression, retinoic acid enters the nucleus of specific target cells, where it binds to retinoic acid receptor proteins; the retinoic acid-protein complex then binds to the regulatory region of DNA. - By affecting gene expression, vitamin A can determine what proteins a cell produces and what type of cell a cell will become as it differentiates. -The ability of vitamin A to regulate the growth and differentiation of cells also makes it essential throughout life for normal reproduction, growth, and immune function.

How Vitamin A Functions in the Body

- In the body the retionoids, which include retinol, retinal, and retinoic acid, are needed for vision (retinal), and for growth and differentiation of cells (retinoic acid). - The carotenoids, specifically beta-carotene, functions to decrease cancer risk and prevent macular degeneration, a role that is independent of the conversion to vitamin A. -Vitamin A is involved in the perception of light. In the eye, the retinal form of the vitamin combines with the protein opsin to form the visual pigment rhodopsin (Figure 9.4). Rhodopsin helps transform the energy from light into a nerve impulse that is sent to the brain. This nerve impulse allows us to see.

Vitamin A Deficiency: Why Vitamin A Deficiency Can Cause Blindness

- Mild vitamin A deficiency causes night blindness. More severe deficiency interferes will cell differentiation. This impairs immune function and growth and causes the epithelial surface of the eye to become hard and dry, leading to infection and blindness. - A spectrum of eye disorders, known as xerophathalmia, is associated with vitamin A deficiency. -When vitamin A is deficient, immature cells cannot differentiate normally, and instead of mucus-secreting cells, they become cells that produce keratin. (b) As xerophthalmia progresses, the drying of the cornea results in ulceration, infection, and ultimately blindness.

Vitamin A Toxicity and Supplements

- Preformed vitamin A can be toxic at doses as low as ten times the RDA and can increase the risk of bone fractures and birth defects. Vitamin A in multivitamins has been related to hip fractures in older women.

Vitamin A in the Diet

- Preformed vitamin A, collectively referred to as the retinoids, is found in animal foods, such as liver, eggs, fish, and fortified dairy products. - The provitamin, or precursor form, collectively referred to as carotenoids, is found in plants, specifically the orange, yellow, or red fruits and vegetables, such as mangos, apricots, cantaloupe, sweet potatoes, and carrots. - All forms of vitamin A in the diet are fairly stable when heated but may be destroyed by exposure to light and oxygen. -Both preformed vitamin A and carotenoids are bound to proteins in foods. To be absorbed, they must be released from the protein by pepsin and other protein-digesting enzymes

Recommendations for Meeting Vitamin D Needs

- Recommended intakes for vitamin D are expressed both in International Units (IUs) and in micrograms. Recommendations are based on the assumption of minimal sun exposure

How Vitamin A Helps Us to See Light

- Retinal binds to opsin in the eye to form rhodopsin. After light strikes rhodopsin to begin the visual cycle, a nerve impulse is sent to the brain so the light is perceived. - When vitamin A is deficient, there is a delay in the regeneration of rhodpsin that causes difficulty seeing in dim light (night blindness).

Meeting Vitamin D Needs with Food and Sunlight

- The RDA for vitamin D assumes limited sun exposure because the amount that is synthesized in the skin is extremely variable.

Other Functions of Vitamin D

- The preventive actions of vitamin D in various disease states, such as cancer, is currently being investigated.

Why Vitamin D is Needed for Healthy Bones

- The principal function of vitamin D is to maintain levels of calcium and phosphorus in the blood that favor bone mineralization with calcium phosphate. - Active vitamin D promotes calcium and phosphorus absorption from the intestines and acts with parathyroid hormone to cause the release of calcium from bone and calcium retention by the kidney. -When vitamin D is deficient, only about 10 to 15% of the calcium in the diet can be absorbed. As a result, calcium is not available for proper bone mineralization and abnormalities in bone structure occur. -In children, vitamin D deficiency causes rickets; it is characterized by weak bones due to inadequate calcium and phosphorus, and bone deformities such as narrow rib cages, known as pigeon breasts, and bowed legs (Figure 9.12). Vitamin D deficiency also prevents children from reaching their genetically programmed height and reduces bone mass and causes muscle weakness

Recommended Vitamin E Intake

- The recommendation for vitamin E intake is based on the amount needed to maintain plasma concentrations of alpha-tocopherol that protect red blood cells membranes from rupturing. The RDA assumes the person is using vegetable oils, as vitamin E functions to decrease the oxidation of the polyunsaturated fats in vegetable oils.

Recommended Vitamin A Intake

- The recommended intake for vitamin A is based on the amount needed to maintain normal stores and is expressed in micrograms of retinol. - Because carotenoids are minimally absorbed unless there is dietary fat and not completely converted to vitamin A, a correction factor (retinol activity equivalent/ RAE) must be applied to carotenoids to determine the amount of usable vitamin A they provide.

Recommended Vitamin K Intake

- Unlike other fat-soluble vitamins, the body uses vitamin K rapidly, so a constant supply is necessary.

Vitamin A Deficiency Remains a World Health Problem

- Vitamin A deficiency is a threat to the health, sight, and lives of millions of children in the developing world. - Vitamin A deficiency can be caused by insufficient intakes of vitamin A, fat, or sometimes animal foods as that is where vitamin A is found -Vitamin A deficiency can be caused by insufficient intakes of vitamin A, fat, protein, or the mineral zinc. As discussed, without fat, vitamin A cannot be absorbed, so a diet very low in fat can cause a deficiency by reducing vitamin A absorption.

When Is Supplemental Vitamin D Recommended?

- Vitamin D supplements are recommended for breast-fed babies, people who do not drink milk, older adults, individuals with dark skin pigmentation and those with limited sun exposure; anyone with low blood levels of vitamin D.

Vitamin D in the Diet

- Vitamin D3 (cholecalciferol) can be made in the skin by exposure to sunlight, so dietary needs vary depending on the amount synthesized. But most people do not make sufficient amounts. - Vitamin D is found in egg yolks, fatty fish, and fortified dairy products, however, is it difficult/ impossible to obtain sufficient vitamin D in the diet.

How Vitamin E Functions in the Body

- Vitamin E functions primarily as a fat-soluble antioxidant. It is necessary for reproduction and protects cell membranes from oxidative damage. Transported on LDL and HDL -Vitamin E functions primarily as a fat-soluble antioxidant. It neutralizes reactive oxygen compounds before they damage unsaturated fatty acids in cell membranes. After vitamin E is used to eliminate free radicals, its antioxidant function can be restored by vitamin C -By neutralizing free radicals, vitamin E guards not only cell membranes, as shown here, but also body proteins, DNA, and cholesterol. Vitamin E must be regenerated by vitamin C to restore it to the form that can act as an antioxidant

Vitamin E Supplements and Toxicity

- Vitamin E is relatively nontoxic with no evidence of adverse effects from consuming large amounts from food. Supplement use has been related to increasing hemorrhagic stroke risk. -There is also some concern of supplement use increasing oxidation.

Vitamin K in the Diet

- Vitamin K is found in plants (phylloquinones), such as spinach, broccoli, and turnip greens; in animal products (menaquinones), such as liver and salmon; and are synthesized by the healthy bacteria that live in the human large intestine. - Vitamin K is destroyed by exposure to light and low- or high-acid conditions.

Vitamin D Deficiency

- When vitamin D is deficient, only about 10 to 15% of calcium in the diet can be absorbed, thus limiting proper bone mineralization. - In children vitamin D deficiency causes rickets; it is characterized by weak bones due to adequate calcium and phosphorus and bone deformities, such as narrow rib cages and bowed legs. While rickets was thought to be eradicated in the US, it is returning due to swaddling of infants and lack of sun exposure. - In adults, vitamin D deficiency causes a condition called osteomalacia which causes bone pain, muscle aches, and an increase in bones fractures. - people with dark skin are at particular risk for vitamin D deficiency due to lesser vitamin D synthesis due to darker pigmentation - The elderly are at risk because the ability to synthesize vitamin D in the skin decreases with age and older adults tend to cover more of their skin and spend less time in the sun.

Vitamin K Deficiency

- While vitamin K deficiency is rare, abnormal blood coagulation is the major symptom of vitamin K deficiency. - Since vitamin K deficiency is a problem in newborns, they are routinely given vitamin K injections at birth.

Vitamin E Deficiency

- With a vitamin E deficiency, red blood cell membranes may rupture, leading to hemolytic anemia. This is most common in premature infants. - As vitamin E is plentiful in the food supply and is stored in many tissues of the body, vitamin E deficiency is rare.

Vitamin A

-Despite our expanding understanding of the functions of vitamin A, deficiency remains a world health problem. -Did you ever hear that eating carrots would help you see in the dark? It turns out to be true. Carrots are high in provitamin A, and vitamin A is important for vision and healthy eyes.

Vitamin E

-Vitamin E (tocopherol) is a fat-soluble vitamin with an antioxidant function. -Several naturally occurring forms of vitamin E are found in foods, but only the alpha-tocopherol (α-tocopherol) form can meet vitamin E requirements in humans.

How Vitamin K Functions in the Body

-Vitamin K is a coenzyme needed for the production of prothrombin and other specific blood-clotting factors (Figure 9.18). Blood-clotting factors are proteins that circulate in the blood in an inactive form. When activated, they lead to the formation of fibrin, the protein that forms the structure of a blood clot. Injuries, as well as the normal wear and tear of daily living, produce small tears in blood vessels. To prevent blood loss, these tears must be repaired with blood clots. - Vitamin K is a coenzyme needed for the production of prothrombin and other specific blood-clotting factors as well as for the synthesis of several proteins involved in bone formation and breakdown.

Vitamin K

-Vitamin K is named for koagulation, the Danish word for coagulation, or blood clotting.

Fat-Soluble Vitamins in Our Diet

-Vitamins A, D, E, and K are soluble in fat, which affects how they are absorbed, transported, stored, and excreted. -Because they are fat soluble, they require special handling for absorption into and transport throughout the body. They require bile and dietary fat for absorption. -Once absorbed, they are transported with lipids through the lymphatic system in chylomicrons before entering the blood (see Chapter 5). Because excesses of these vitamins can be stored in the liver and fatty tissues, intakes can vary without a risk of deficiency as long as average intake over a period of weeks or months meets needs.

Vitamin A as a Drug

Vitamin A supplements and derivatives of vitamin A used as drugs cannot be substituted as a treatment for acne, and large doses will cause toxicity symptoms.

Vitamin D

Vitamin D is known as the "sunshine vitamin" because it can be produced in the skin by exposure to ultraviolet light.

Rickets

it is characterized by weak bones due to adequate calcium and phosphorus and bone deformities, such as narrow rib cages and bowed legs. While rickets was thought to be eradicated in the US, it is returning due to swaddling of infants and lack of sun exposure.