Jamie Pope, Steven Nizielski, and Alison McCook NUTRITION for a Changing World FIRST EDITION Chapter 10 Fat-Soluble Vitamins Soak Up the Sun? © 2016 by W. H. Freeman and Company & Scientific American

Chapter 10 Objectives Identify the fat-soluble vitamins and their primary functions Describe the properties of the fat-soluble vitamins Describe the role of vitamin D in blood calcium regulation Identify excellent dietary sources of the fat-soluble vitamins Describe the role of vitamin A in healthy vision List sources of free radicals and describe how antioxidants can block oxidative damage Explain how vitamin E works as an antioxidant in the cell membrane

Kimani the Gorilla Dying from vitamin D deficiency Has rickets Bone malformation and muscle weakness Treated with tenfold the normal dose of vitamin D supplementation In 2005 Michael Holick, PhD, MD, (an endocrinologist) was called to see a 7-month-old gorilla born in captivity at Franklin Park Zoo. The gorilla exhibited signs of rickets, but a normal dose of vitamin D didn’t make much difference. Dr. Holick recommended tenfold the normal dose, and she responded. She will likely never be as tall as other gorillas, but she improved.

Vitamins Organic compounds Micronutrients Essential nutrients Individual units

Vitamins Bioavailability Solubility Determinant of absorption and transportation process Affects where they are stored and risk for toxicity Fat-soluble Vitamins A, D, E, and K Water-soluble B vitamins, choline, and vitamin C

Properties of Fat-Soluble Vitamins

Vitamin D “Sunshine vitamin” Made in skin From cholesterol and UV light Not enough sun exposure makes it essential to consume in diet Activated in the kidneys and liver

Sources of Vitamin D

Functions of Vitamin D Acts as a hormone Helps bone growth and maintenance Regulates calcium Regulates protein synthesis Possibly regulates cardiovascular function

Vitamin D Activation Calcitriol: fully activated form from the kidney

Regulation of Blood Calcium Calcitriol increases absorption of calcium in the intestine Active vitamin D and parathyroid hormone decrease calcium excretion by the kidneys

Vitamin D Deficiency Evidence that deficiency may increase risk of Rickets (in children) Osteomalacia (in adults) Cancer Autoimmune disease Kidney disease Type 2 diabetes Cardiovascular disease

Vitamin A Retinoids Carotenoids Preformed as already in active form Retinal Retinol Retinoic acid Carotenoids Provitamin, not in active form Beta-carotene Retinol is the only retinoid present in our diet. It is readily converted to retinal or retinoic acid in the body. These are the active forms of vitamin A. Carotenoids are provitamins, as they must be converted in the body into one of the active forms of the vitamin. The primary carotenoid is beta-carotene.

Sources of Vitamin A Preformed Provitamin A carotenoids Animal foods and fortified foods In the United States and Canada: reduced- and low-fat milk and yogurt must be fortified due to loss during the removal of fat Provitamin A carotenoids Yellow-, orange-, and red-pigmented fruits and vegetables RDA given as mcg of retinol activity equivalents (RAE) Conversion of beta-carotene to retinol is never complete Absorption of carotenoids from food is poor Slicing, chopping, cooking, juicing, and cooking can improve bioavailability

Dietary Sources of Vitamin A

Functions of Vitamin A Vision Cell development Immune function Growth Bone health Reproduction In all functions except vision, vitamin A acts as a hormone by controlling the synthesis of numerous proteins encoded in our genes.

Vitamin A in Vision Key component of rhodopsin

Oxidation Source of free radicals and their effects

Antioxidants Plant forms of vitamin A Carotenoids and beta-carotene Eating foods rich in carotenoids is associated with less risk for cancer, but research suggests that supplements may actually increase cancer risk.

Vitamin A Deficiency Hypovitaminosis A Night blindness Permanent blindness Impaired immunity Rough, dry, or scaly skin Keratinization

Vitamin A Toxicity Hypervitaminosis A UL for adults is 3,000 mcg RAE Can cause osteoporosis Comes mostly from supplements UL for adults is 3,000 mcg RAE Pregnant women need to be cautious Can cause birth defects Animal foods and supplements Excess of plant sources does not cause toxicity Beta-carotene can turn your skin yellow

Vitamin E Tocopherols RDA for 19 years and older is 15 mg or 22.4 IU Dietary sources

Functions of Vitamin E Antioxidant

Vitamin E Toxicity UL = 1,000 mg or 1,500 IU Caused by high supplement intake Increases tendency to bleed

Vitamin K Produced by bacteria in the intestine Dietary sources The requirements are given in Adequate Intake (AI) amounts since current knowledge does not provide sufficient evidence to establish a specific RDA.

Functions of Vitamin K Blood clotting Bone metabolism Needed for synthesis of protein for blood clotting Bone metabolism Modifies bone proteins

Vitamin K Deficiency Hemorrhaging Antibiotic use can kill intestinal bacteria and decrease this source of vitamin K. Anticoagulants interfere with the metabolism of vitamin K to help prevent blood clotting. Those on these medications must strive to keep vitamin K intake consistent, as the vitamin can interfere with the medication. Since the early 1960s, infants receive vitamin K at birth to reduce the risk of hemorrhage because they have limited stores and lack bacteria to produce vitamin K.

Summary Vitamins are organic compounds (containing both carbon–carbon and carbon–hydrogen bonds) that are needed in small quantities for very specific functions, such as the maintenance of regulatory and metabolic processes in the body Most vitamins are in their active form (preformed) in foods; however, in some cases, inactive, precursor forms of vitamins, called provitamins, must be converted to fulfill biological functions in the body Inadequate or excessive intake of vitamins can lead to deficiency or toxicity, with adverse health effects The 14 known vitamins are classified by their solubility, as fat-soluble or water-soluble The fat-soluble vitamins (A, D, E, and K) have diverse functions in the body

Summary (Cont’d) Fat-soluble vitamins are transported in the body via the lymph, and excess intake is stored in fatty tissues and the liver, from which the vitamins are released when needed The body derives vitamin A from preformed A (retinol) found in animal foods and fortified foods, and to a lesser degree from provitamin A carotenoids in plant foods, as conversion to the active form is incomplete Vitamin A serves many critical biochemical and physiological functions in the body related to vision, cell development, reproduction, immune function, and growth, among others; the carotenoids have antioxidant properties in the body, which help protect cells from damage caused by free radicals

Summary (Cont’d) Vitamin D, which functions as a hormone in the body, is actually not considered an essential nutrient in the diet unless there is inadequate sun exposure because it can be synthesized from cholesterol through exposure of the skin to UV light; among other important functions, vitamin D plays a key role in the growth and maintenance of bone, in part through its role in maintaining calcium concentrations in the blood Serving primarily as an antioxidant in the body, vitamin E is a group of compounds called tocopherols, found primarily in nuts and vegetable oils Vitamin K is an essential nutrient found in foods such as leafy greens; a significant amount of our daily requirements may also be produced by bacteria in the intestine Vitamin K plays a key role in blood clotting and bone metabolism