Chapter 9 Fat-Soluble Vitamins
Vitamins Were Discovered about One Hundred Years Ago
Each new vitamin was given a temporary name when it was discovered. Naming of vitamins follows the letters of the alphabet, starting with A; we are now at the letter K. • A, B, C, D, E, and K • Vitamins F, G, and H were dropped.• The nomenclature changed when vitamin B was found to have several functions. • Subscripts were added for each new isolated role.
Some Foods Are Fortified with Vitamins
Fortified foods: Voluntary addition of nutrients by manufacturers to: • Enhance the nutrient quality of food• Prevent or correct dietary deficiencies• Ensure adequate intake for some individuals Enrichment is a form of fortification. Fortification can contribute to health risks. • Lead to vitamin excess• Displace nutrient-rich foods
Retinol
Found in animal foods Stored in the body Function: Reproduction
Retinal and Retinoic Acid
Found in plants Retinal function: Vision Retinoic function: Regulates growth
Age-related macular degeneration (AMD)
Free radical damage to the macula in the eye Most common cause of vision impairment in Americans over 60 years AMD risk and loss of vision may be reduced with supplementation. • Vitamin C, vitamin E, beta-carotene • Zinc and copper
What Are Vitamins?
-Tasteless, organic compounds -Required in small amounts
What Is Vitamin A?
A family of fat-soluble retinoids (retinol, retinal, retinoic acid)
Vitamin D Toxicity
A high intake can cause loss of appetite, nausea, vomiting, and constipation. Overuse of supplements may lead to hypervitaminosis D. Hypercalcemia Can cause damaging calcium deposits in kidneys, lungs, blood vessels, and heart Can affect the nervous system and cause severe depression Too-high levels are rarely caused by food intake or overexposure to the sun.
Metabolic Functions of Vitamin E
Acts as a powerful antioxidant • Protects cell membranes; prevents oxidation of LDL cholesterol Acts as an anticoagulant, inhibiting formation of harmful clots inside bloodstream • No evidence supporting a role in prevention of cancer or other diseases has been conclusively identified.
Vitamin A Absorption and Transport
All forms of vitamin A are absorbed by active transport with bile salts and micelles. Beta-carotene is absorbed by passive diffusion. • Reduced with high fiber intake• Improved in cooked foods Most forms of vitamin A are packaged into chylomicrons enter lymph. Retinoic acid is attached to albumin. Stored in the liver
All Vitamins Are Organic, but Differ in Structure and Function
All vitamins contain carbon, hydrogen, and oxygen. • Some vitamins contain nitrogen, cobalt and sulfur. • The chemical structure of each vitamin is unique. • Each vitamin is a singular unit and absorbed intact. • Vitamins perform numerous essential functions. • Some vitamins have more than one role in metabolism.
What Is Vitamin E?
Alpha-tocopherol is the most active form in the body. • The synthetic form in supplements is only half as active as the natural form. Absorbed with bile salts and micelles• Packaged in chylomicrons ⟶ lymph ⟶ circulation ⟶ liver• Ninety percent of vitamin E is stored in adipose tissue.
How Do Vitamins Differ in Their Absorption and Storage?
Bioavailability varies based on: Amount in food Preparation Efficiency of digestion and absorption of food Individual nutritional status Natural or synthetic Fat-soluble vitamins are generally less bioavailable than water-soluble vitamins. Vitamins from plant foods are generally less bioavailable than those in animal foods.
Metabolic Functions of Vitamin D
Bone growth Calcitriol stimulates intestinal calcium and phosphorus absorption. Maintains healthy ratio of calcium and phosphorus in the blood Controls interaction between osteoblasts and osteoclasts • May prevent some cancers • Incidence of breast, colon, and prostate cancer is higher in individuals living in sun- poor areas of the world. Potentially helps reduce risk of some autoimmune disorders • May prevent diabetes • May reduce type 1 diabetes risk by 50 percent in adults • Type 2 diabetes is associated with low blood vitamin D levels. • May regulate blood pressure
• Free radicals
By-products of body's metabolic reactions Molecules with an unpaired electron, which makes them unstable Factors that increase free radical production include: • UV light• Exposure to toxins from smoking• Exposure to environmental pollutants Oxidative stress occurs when free radicals accumulate faster than the body can metabolize them. Damages DNA and body proteins, and alters cell structure Excess free radicals contribute to chronic diseases. • Heart disease• Cancer• Aging • Diabetes • Parkinson's disease • Alzheimer's disease
What Is Vitamin D?
Called the "sunshine vitamin" Derived from a reaction between ultraviolet rays and a form of cholesterol in the skin • Exposure to sunlight can synthesize all of the body's vitamin D needs.• Considered a conditionally essential nutrient Considered a prohormone Found in two forms Cholecalciferol (vitamin D3): Produced in the skin and found in animal foods Ergocalciferol (vitamin D2): Found in plants and dietary supplements
There Are Criteria for Designating Vitamins
Cannot be synthesized in ample amounts in the body Chronic deficiency is likely to cause physical symptoms. Symptoms will disappear once the vitamin level in the body is restored. • Deficiency can cause permanent damage. Thirteen compounds meet the above criteria.
Vitamin A Deficiency
Chronic vitamin A deficiency causes night blindness. Prolonged vitamin A deficiency leads to xerophthalmia. • Leading cause of preventable blindness in children, mostly in developing countries Deficiency can lead to keratinization of epithelial tissues. Epithelial cells don't secrete mucus. Cells are unable to function properly, promoting infection.
Vitamin A Toxicity
Excessive amounts of preformed vitamin A can accumulate to toxic levels. Toxic levels occur by taking supplements, not with food intake. >15,000 μg can cause symptoms of toxicity. Hypervitaminosis A can lead to liver damage and even death. Overconsumption: During pregnancy can cause birth defects in the face, skull, and CNS of the child Can potentially result in osteoporosis and bone fractures in adults Carotenoids in foods are not toxic. Do not pose serious health problems Excess carotenoids can cause carotenodermia. • Overconsuming beta-carotene supplements • May increase a smoker's lung cancer risk
What Are Antioxidants?
Group of compounds that neutralize free radicals, helping to counteract the oxidation that takes place in cells • Includes:• Vitamin E • Vitamin C • Selenium • Flavonoids • Carotenoids
are vitamin supplement good for health
May be helpful for some individuals Pregnant and lactating women Older individuals who need vitamin B12 Individuals who lack dietary vitamin D or sun exposure Individuals on low-kilocalorie diets Strict vegetarians Individuals with food allergies or lactose intolerance Individuals who abuse alcohol Individuals who are food insecure Breast-fed infants
• Supplements
No evidence supports the use of supplements and preventing chronic diseases or cognitive decline. Not a substitute for healthy eating Can cause adverse side effects Supplements:• Are not regulated like drugs and do not require FDA approval to be put on the market • Supplements can't be removed unless they have been shown to be unsafe or cause harm. • How to choose a supplement Choose supplements with the United States Pharmacopeial Convention seal (USP). Read the label carefully.
Metabolic Functions of Vitamin A
Participates in: Vision Protein synthesis & cell differentiation Reproduction Bone health A healthy immune system• May help fight cancer • Carotenoids are antioxidants.
Metabolic Functions of Vitamin K
Promotes blood clotting • Involved in synthesizing four blood-clotting factors Promotes strong bones• Assists with the carboxylation of other proteins • Interacts with proteins osteocalcin and matrix Gla protein, which is essential for the formation of a strong bone matrix
Vitamin toxicity (hypervitaminosis):
Rare Results from ingesting excess vitamins, which leads to tissue saturation Can damage cells, sometimes permanently Results from supplementing with megadoses of vitamins; does not occur from eating foods The Dietary Reference Intakes include a tolerable upper intake level (UL) for most vitamins, to prevent excess.
Functions
Regulate metabolism Help convert energy in fat, carbohydrate, and protein into ATP Promote growth and reproduction
Vitamin D Deficiency
Rickets: Vitamin D deficiency disease in children Bones aren't adequately mineralized with calcium and phosphorus, causing them to weaken, leading to bowed legs. On the rise in the United States due to decreased milk consumption, fear of skin cancer from sun exposure, and air pollution Other vitamin D deficiency disorders Osteomalacia: Adult equivalent of rickets Osteoporosis: Condition where bones don't mineralize properly Muscle and bone weakness and pain
• Provitamins
Substances found in foods that are not directly usable by the body Converted to an active form once absorbed Example: beta-carotene vitamin A
Daily Needs—Vitamin D
Sun exposure cannot meet everyone's vitamin D needs. The skin pigment melanin and use of suncreens reduce vitamin D production. Sunlight intensity during winter in some locations is not sufficient to make enough vitamin D.
Cataracts
The lens of the eye becomes cloudy; common eye disorder in older adults.
What Is Vitamin K?
Three forms of vitamin K • Phylloquinone is found in green plants. • Menaquinone is synthesized by intestinal bacteria. • Menadione is the synthetic form
There Are Criteria for Classifying Vitamins
Vitamins are classified based on solubility. • Nine water-soluble: • B vitamin complex• Vitamin C • Fourfat-soluble: • Vitamin A • Vitamin D • Vitamin E • Vitamin K
• Preformed vitamins
Vitamins found in foods in their active form • Do not need to be converted
Water-Soluble Vitamins Are Not Stored after Absorption
• Absorption Absorbed with water and enter directly into the bloodstream Most absorbed in the duodenum and jejunum • Excretion• Not stored in the body• Excess intake excreted through the urine • Important to consume adequate amounts daily • Dietary excesses can be harmful.
Fat-Soluble Vitamins Are Stored after They Are Absorbed
• Absorption• Attached to proteins in foods, released in the stomach and absorbed in the duodenum• Packaged in chylomicrons lymph bloodstream • Lack of fat can lead to deficiency. Storage• Liver - main storage site for vitamin A; to a lesser extent for vitamins K and E.• Vitamin D mainly stored in the fat and muscle tissue. • Can build up in the body to the point of toxicity
What Are Antioxidants? (cont'd)
• Antioxidant-rich foods also contain other protective compounds. • These sources also act as antioxidants, stimulate the immune system, and interact with hormones to prevent cancers. • Phytochemicals are naturally occurring plant compounds. • Carotenoids • Flavonoids• Antioxidants and phytochemicals from the diet have more health benefits than those from supplements.
Vitamins Can Be Destroyed during Cooking or Storage
• Exposure to oxygen• Water-solublevitamins • Vitamins A, E, and K • Exposure to ultraviolet light• Riboflavin• Beta-carotene and vitamin C
Vitamin K Absorption and Transport
• Most vitamin K is absorbed in the jejunum.• Ten percent of vitamin K is produced by bacteria in the colon. • Vitamin K is incorporated into chylomicrons and transported to the liver. • When a diet is deficient in vitamin K:• Storage forms are transported by VLDL, LDL, and HDL.• Stored mostly in the liver
Vitamin K Toxicity and Deficiency
• Toxicity No known adverse effects Individuals taking anticoagulant medications should keep vitamin K intake consistent.• Changes in intake can increase or decrease drug effectiveness. • Deficiency Infants are born with too little vitamin K. Deficiency severe enough to affect blood clotting is extremely rare. May cause hip fracture in older men and women
Vitamin E Toxicity and Deficiency
• Toxicity• No known risk of consuming too much vitamin E from natural food sources • Overconsumption of synthetic form in dietary supplements and fortified foods can increase risk of a hemorrhage • Deficiency Rare Chronic deficiency of vitamin E can cause nerve problems, muscle weakness, and free radical damage to cell membranes.
Vitamins Can Be Destroyed during Cooking or Storage (cont'd)
• Water• Most water-soluble vitamins • Changes in pH• Thiamin and vitamin C • Heat• Most water-soluble vitamins, especially vitamin C Preserve Your Vitamins!
What Are the Best Sources of Vitamins?
• Wholefoods Fruits, vegetables, and whole grains Rich in vitamins, phytochemicals, antioxidants, and fiber • Dietary Guidelines for Americans recommends: Eat a wide variety of foods from each food group, with ample amounts of vitamin-rich fruits, vegetables, whole grains, and dairy foods. Most people do not need supplements.
