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Vitamin D For Dummies®

Visit www.dummies.com/cheatsheet/vitamind to view this book's cheat sheet.

Table of Contents

Introduction
About This Book
Conventions Used in This Book
What You Don’t Have to Read
Foolish Assumptions
How This Book Is Organized
Part I: The Life History of Vitamin D
Part II: Key Roles of Vitamin D
Part III: Getting Enough
Part IV: The Part of Tens
Icons Used in This Book
Where to Go from Here
Part I: The Life History of Vitamin D
Chapter 1: The Essentials of Vitamin D
Understanding What Vitamin D Is and How It Works
Forming vitamin D in the body
Regulating the production of vitamin D
Moving vitamin D around the body
Putting vitamin D to work
Seeing How Vitamin D Affects Your Health
Building bone
Reducing your risk of cancer
Preventing heart disease and diabetes
Checking Out Where Vitamin D Comes From
Sun
Food
Supplements
Appreciating the Long-Term Medical Benefits
Prevention of deformity
Lives saved?
Chapter 2: Finding Out If You Have Enough Vitamin D
How Much Do You Need, Anyway?
Knowing what level of vitamin D your body needs
Computing the correct IU level
Checking out the government’s recommendations
Avoiding a vitamin D overdose
Measuring Vitamin D in the Body
Checking Children for Proper Vitamin D Levels
Delivering the right daily dose for kids
Treating children for deficiency
Figuring Out Who Lacks Vitamin D
Caucasians
African Americans
Asian Americans
Latinos
Children
The elderly
People who are obese
Looking at Lab Tests for Vitamin D
Examining the tests
Discovering testing problems
Standardizing the test
Chapter 3: Considering Calcium
Understanding the Physiology of Calcium
Considering the functions of calcium
Learning how calcium is controlled
Getting the Calcium You Need
Following the U.S. government’s guidelines on calcium
Selecting the best sources of calcium
Dealing with too much and too little calcium
Realizing the Purpose of Other Minerals for Bone
Focusing on phosphorus
Giving credit to magnesium
Part II: Key Roles of Vitamin D
Chapter 4: Facilitating Bone Growth and Strength
Recognizing the Importance of Bone
Mechanical functions of bone
Synthetic function of bone
Metabolic functions of bone
Building Strong Bones with Vitamin D
What is bone?
Vitamin D brings in the calcium and promotes bone growth
Reckoning with Rickets and Osteomalacia
Describing signs and symptoms
Exploring the causes
Treating the condition
Managing Osteoporosis
Looking at the risk factors
Diagnosing osteoporosis
Preventing osteoporosis
Treating osteoporosis
Helping Your Teeth Grow
Exploring the normal development of teeth
Knowing how rickets affects teeth
Chapter 5: Protecting the Immune System
Describing the Immune System
Separating the innate from the adaptive immune system
Calling on B and T cells for protection
Realizing the Role of Vitamin D
Boosting the Immune System to Fight Infections
Healing tuberculosis
Fending off flu and other viruses
Examining Autoimmune Diseases
Multiple sclerosis
Rheumatoid arthritis
Systemic lupus erythematosis
Graves’ disease
Chapter 6: Preventing Cancer
Explaining How Cancer Develops
Understanding how cell growth gets out of control
Checking out the different types of tumors
Moving through the stages of cancer
How Vitamin D Helps Prevent the Big C
Promoting normal cell growth
Encouraging the death of abnormal cells
Protecting cells from things that cause cancer
Taking steps if you already have cancer: Vitamin D’s effect
Blocking Colon Cancer
Reviewing colorectal cancer
Understanding vitamin D’s possible role
Stopping Breast Cancer
Reviewing breast cancer
Understanding vitamin D’s role
Looking at Prostate Cancer
Reviewing prostate cancer
Understanding vitamin D’s role
Vitamin D and Other Cancers
Halting lung cancer
Deterring ovarian cancer
Fending off pancreatic cancer
A Caveat about Vitamin D and Cancer
Chapter 7: Safeguarding Your Heart
Considering the Link between Vitamin D and Heart Disease
Coronary Artery Disease: It Can Creep Up on You
Fingering cholesterol as the culprit
Looking at vitamin D’s effect on CAD
High Blood Pressure: When High Numbers Are Harmful
Explaining high blood pressure
Clarifying vitamin D’s role in blood pressure
Heart Failure: When the Body’s Pump Is Weak
Explaining heart failure
Examining vitamin D’s role in heart health
Heart Attacks and Vitamin D: Seeing the Bigger Picture
Relationship of vitamin D levels and risk of a heart attack
Can increasing vitamin D after a heart attack prevent another one?
Realizing There’s More to Learn About Vitamin D and the Heart
Chapter 8: Avoiding Diabetes and Related Conditions
The Basics of Diabetes
Identifying the symptoms of diabetes
Making a diagnosis
Type 1 Diabetes: When the Body Attacks Itself
Describing type 1 diabetes
Treatment and prognosis
Examining vitamin D’s role in type 1 diabetes
Type 2 Diabetes: When Your Body Reacts to Your Lifestyle
Looking at the characteristics of type 2 diabetes
Treatment and prognosis
Checking out vitamin D’s role in type 2 diabetes
Metabolic Syndrome: A Dangerous Precursor to Heart Disease and Diabetes
Determining who’s at risk for metabolic syndrome
Recognizing major signs and symptoms
Dealing with metabolic syndrome
Connecting metabolic syndrome and vitamin D
Polycystic Ovary Syndrome: A Leading Cause of Female Infertility
Recognizing major signs and symptoms
Dealing with polycystic ovary syndrome
Connecting polycystic ovary syndrome and vitamin D
Chapter 9: Looking at Other Possible Functions of Vitamin D
Finding a Role for Vitamin D in Asthma
Reviewing asthma
Understanding the role of vitamin D
Treating Psoriasis
Reviewing psoriasis
Understanding the role of vitamin D
Linking Vitamin D Levels and Brain Health
Normal brain development
Autism
Alzheimer’s disease
Parkinson’s disease
Depression
Seasonal affective disorder
Managing Your Weight
Looking at Fibromyalgia
Chapter 10: Furthering Science’s Knowledge of Vitamin D
Seeing the Importance of Research Studies
How research studies work
Participating in research studies
A Big Vitamin D Study That’s Trying to Do Everything
Part III: Getting Enough
Chapter 11: Getting Vitamin D from the Sun
Catching Some Rays
Checking out ultraviolet rays
A cautionary word about tanning and tanning salons
Seeing How the Skin Responds to the Sun
How skin wrinkles
How skin tans (and eventually burns)
Knowing How Much Vitamin D You Can Make from the Sun
Figuring your minimal erythemal dose
Determining your skin type
The Whens and Wheres of Getting the Right Amount of Sun
Calculating optimal sun-exposure times for making vitamin D
Enjoying the sun in different seasons
Enjoying the sun at different latitudes
Enjoying the sun at different times of day
The role that altitude and atmosphere play
Blocking Out the Sun
Seeing how sunscreen protects your skin
Choosing and using sunscreen
Considering the Risks of Sun Exposure
Premature aging
Skin cancer
Is There Such a Thing as Safe Sun?
Chapter 12: Getting Vitamin D from Food
Selecting the Best Sources of Vitamin D
Cod liver oil
Salmon
Mushrooms
Mackerel
Tuna fish
Milk
Orange juice
Other sources
Obtaining Vitamin D If You Have Dietary Restrictions
If you’re a vegetarian
If you can’t absorb fats
Chapter 13: Getting Vitamin D from Supplements
Choosing the Best Supplement
Deciding what to take
Choosing a multivitamin, mineral, or targeted supplement
Deciding how much to take
Comparing the different preparations of vitamin D
Taking Vitamin D Supplements Correctly
Drugs that interfere with absorption
Medical conditions that increase your need for vitamin D
Determining a Supplement’s Effect on Blood Levels of Vitamin D
Chapter 14: Appreciating Special Needs in Pregnant Women and the Elderly
Understanding Why Older Folks Need More Vitamin D
Seeing the Benefits of Vitamin D as You Age
Avoiding falls and fractures
Slowing muscle loss
Preventing pelvic floor disorders in women
Improving memory and thinking
Getting Sufficient Vitamin D for Mother and Newborn
Understanding how vitamin D influences a baby’s development
Preparing for a pregnancy with vitamin D
Getting enough vitamin D for two during pregnancy
Making sure your newborn gets the right amount of vitamin D
Part IV: The Part of Tens
Chapter 15: Ten Myths Regarding Vitamin D
Myth: Vitamin D Is a Vitamin
Myth: You Can Get Sufficient Vitamin D in Your Diet
Myth: You Should Avoid the Sun at All Costs
Myth: It’s Easy to Take Too Much Vitamin D
Myth: Government Guidelines for Vitamin D Intake Are Inadequate
Myth: You Need Vitamin D Only for Your Bones
Myth: Children Get Enough Vitamin D in Breast Milk
Myth: You Protect Your Skin Completely with Sunscreen
Myth: A Tanning Salon Is a Safe Way to Expose Your Skin
Myth: Vitamin D Is the Cause for Elevated Serum Calcium
Chapter 16: Ten Possible New Functions of Vitamin D
Treating Cystic Fibrosis
Reducing Skin Rashes and Swelling
Helping with Chronic Obstructive Pulmonary Disease
Improving In Vitro Fertilization Rates
Preserving Bone in Burn Patients
Relieving Chronic Lower Back Pain
Healing Hip Fractures
Slowing the Progression of Osteoarthritis
Avoiding Chronic Sinusitis
Preventing Nocturnal Cramps
Cheat Sheet

Vitamin D For Dummies®

by Alan L. Rubin, MD

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About the Author

Alan L. Rubin, MD, is an endocrinologist who has practiced in San Francisco for more than 35 years. Dr. Rubin was an Assistant Clinical Professor of Medicine at the University of California Medical Center in San Francisco for 20 years. He has spoken about topics in endocrinology to both professional medical audiences and nonmedical audiences around the world. His interest in diabetes first led him to a study of vitamin D. Dr. Rubin is also a professional member of the Endocrine Society.

Dr. Rubin began writing For Dummies books with Diabetes For Dummies in 1999. Since then, Dr. Rubin has had five other bestselling For Dummies books — Diabetes Cookbook For Dummies, Thyroid For Dummies, High Blood Pressure For Dummies, Type 1 Diabetes For Dummies, and Prediabetes For Dummies — all published by Wiley Publishing. His six previous books cover the medical problems of 150 million Americans.

Dr. Rubin has now written a total of 13 For Dummies books, with first, second, and third editions. His books have been translated into 15 languages.

Dedication

This book is dedicated to my patients, who have taught me so much and made my decision to become a physician the exact right one for me. Over these many years, I have laughed with them, cried with them, and enjoyed their willingness to open their lives to me. I’ve become friends with too many patients to name. I want to recognize some of them by their first names (you know who you are), in no particular order. Forgive me if I’ve inadvertently left you out.

/ffirstb01

Author’s Acknowledgments

For this first edition, acquisitions editor Michael Lewis deserves major thanks. I have had the pleasure of working with him for several years. He is supportive, encouraging, and fun, and I look forward to a long association with him. I am also blessed with another great project editor, Vicki Adang, who not only made sure that everything was readable and understandable, but also offered excellent suggestions to improve the book. My thanks also to Dr. Jim Fleet for reviewing the book.

Publisher’s Acknowledgments

We’re proud of this book; please send us your comments through our online registration form located at http://dummies.custhelp.com. For other comments, please contact our Customer Care Department within the U.S. at 877-762-2974, outside the U.S. at 317-572-3993, or fax 317-572-4002.

Some of the people who helped bring this book to market include the following:

Acquisitions, Editorial, and Media Development

Project Editor: Victoria M. Adang

Acquisitions Editor: Michael Lewis

Copy Editors: Krista Hansing, Susan Hobbs

Assistant Editor: David Lutton

Contributing Technical Editors: James C. Fleet, PhD., Department of Foods and Nutrition, Purdue University; Christopher S. Kovacs, MD, FRCPC, FACP; Professor of Medicine (Endocrinology), Obstetrics and Gynecology, and BioMedical Sciences, Memorial University of Newfoundland

Editorial Manager: Michelle Hacker

Editorial Assistants: Rachelle Amick, Alexa Koschier

Art Coordinator: Alicia B. South

Cover Photo: ©iStockphoto.com/Les Cunliffe

Cartoons: Rich Tennant (www.the5thwave.com)

Composition Services

Project Coordinator: Kristie Rees

Layout and Graphics: Nikki Gately, Joyce Haughey, Corrie Socolovitch

Proofreader: Tricia Liebig

Indexer: Infodex Indexing Services, Inc.

Illustrator: Kathryn Born

Publishing and Editorial for Consumer Dummies

Diane Graves Steele, Vice President and Publisher, Consumer Dummies

Kristin Ferguson-Wagstaffe, Product Development Director, Consumer Dummies

Ensley Eikenburg, Associate Publisher, Travel

Kelly Regan, Editorial Director, Travel

Publishing for Technology Dummies

Andy Cummings, Vice President and Publisher, Dummies Technology/General User

Composition Services

Debbie Stailey, Director of Composition Services

Introduction

When the French philosopher Voltaire published Candide, or Optimism, 250 years ago, his purpose was to prove the opposite of what his character Pangloss claimed, that this is the “best of all possible worlds.” Candide was an attempt to show that the world is filled with horror and folly. After you have read my book, though, you may choose to side with Pangloss. Vitamin D could be such a panacea. From asthma to xeroderma pigmentosum and a lot in between, research suggests that vitamin D might be a modern version of a cure-all. Remember, there are two Ds in Candide!

For good reason, within the past few years a blood test for 25-hydroxyvitamin D has become commonly ordered in the United States. Doctors are finding many people whose blood levels have slipped below where some medical experts believe they should be. Low blood levels occur in all ages of Americans and throughout the world. Amazingly, reversing this lack of vitamin D is relatively easy and inexpensive, as you discover in Part III of this book.

What explains this lack of vitamin D in our bodies? First, many of us live in temperate zones where the rays of the sun aren’t powerful enough to produce vitamin D in our skin for much of the year. Second, even where the sun can produce sufficient vitamin D, we have been warned so often about the danger of the sun’s rays that we cover ourselves with sunscreen, clothing, and hats so that the healing power of the sun can’t penetrate. By the time you finish this book, you’ll know how to expose yourself for the right amount of time without risking wrinkles or skin cancer.

About This Book

This book has the latest information in the very fast-moving field of vitamin D and your health. As a long-time For Dummies author, I have written this book using everyday language so everyone can understand the material — no formal training in the sciences required.

Conventions Used in This Book

The following conventions are used throughout the text to make it consistent and easy to understand:

check.png The unit in which 25-hydroxyvitamin D, the serum measure for how much vitamin D you have in your body, is measured in nanograms per milliliter (ng/ml) in the United States and nanomoles per liter (nmol/l) in Canada and much of the rest of the world.

check.png Calcitriol is the biologically active form of vitamin D and does all of the things that we attribute, indirectly, to vitamin D.

check.png All web addresses appear in monofont.

check.png New terms appear in italic and are closely followed by an easy-to-understand definition.

check.png Bold is used to highlight keywords in bulleted lists.

You should also know vitamin D comes in two forms. Chole-calciferol, the form of vitamin D that comes from the sun acting on your skin, is also called vitamin D3. This is also the form you get from foods that come from animals. Ergocalciferol, a form of vitamin D contained in many supplements and which is also found in some plants like irradiated mushrooms, is also called vitamin D2. I try not to use those long names again, but you should be aware of them.

What You Don’t Have to Read

From time to time, I explain some complicated subjects or include some information that’s interesting but not essential to your understanding of vitamin D. I’ve shaded this text in gray. This means that you can skip this information, but if you have a deep, questioning mind, you might want to read it. The information in gray is for the person who really wants to know the nuances of vitamin D.

Foolish Assumptions

As I wrote this book, I assumed that you know nothing about vitamin D. If you already know a little bit about vitamin D, you can skip the stuff you know and just go to the stuff you want to know. But you may miss out on some new findings or miss the opportunity to learn some things in much greater detail than what you may already know.

I expect that you’ll be amazed by the great potential of vitamin D as an agent that can protect your health. Feel free to highlight points that are of interest to you or that you want to find out more about. After all, you paid for the book (I hope).

How This Book Is Organized

This book has four parts. You don’t have to start at Part I, but I recommend that you do so. Each part is self-contained, so you can jump to Chapter 12 if that’s what floats your boat. Here’s a brief discussion of the contents of each part.

Part I: The Life History of Vitamin D

Part I is an introduction to vitamin D. It tells you what this so-called vitamin actually is and does, and how it performs its actions. It also tells you how to find out if you have enough in your body. You can find out which populations often lack sufficient vitamin D and how to overcome this. You will discover how vitamin D is measured and the problems associated with testing for vitamin D. Vitamin D also has an important sidekick, calcium, and you’ll read about that substance here as well.

Part II: Key Roles of Vitamin D

In Part II, you explore the role of vitamin D in the various organs of the body and how it prevents diseases. You quickly come to understand how important this nutrient has become in the last few years.

The chapters in these parts cover everything from the role of vitamin D in bone growth — where the function of vitamin D was thought to begin and end — to its potential role in preventing and treating heart disease, cancer, diabetes, and other common health concerns.

Part III: Getting Enough

Now that you’re convinced that you must maintain sufficient vitamin D in your body, Part III helps you do just that. Fortunately, you can build up your blood levels in many ways.

Chapter 11 describes how our bodies have gotten vitamin D for centuries for free, from the giver of life: our sun. The sun has gotten a bad name from skin doctors in the last few years, but I intend to set the record straight. The next best source is food, discussed in Chapter 12.

The next chapter takes up the subject of vitamin D supplements. What’s the best way to take it? How much and when should you take it? What should be the effect of a given dose? You can get 2,000 international units of vitamin D for so cheap that there’s no excuse for being low in vitamin D.

Part IV: The Part of Tens

Finally, Part IV is the traditional Dummies Part of Tens — in this case, ten myths about vitamin D and ten new functions of this vitamin. We may have to make this the Part of Twenties in future editions, given the research about vitamin D, but this works for now.

Icons Used in This Book

Icons throughout the book alert you to information you must know, information you may find helpful, and information you need to heed to live a healthy life.

Remember.epsWhen you see this icon, it means that the information is essential and you should be aware of it. Read it twice.

Tip.epsThis icon marks important information that can increase the benefits of vitamin D on your health.

warning_bomb.epsThis icon alerts you to potential health pitfalls or setbacks.

Where to Go from Here

This book doesn’t have to be read starting at page 1 straight to the end. It’s not a novel, after all. (If you’d like to make it into a movie, though, let me know. I have just the right person for the leading role.)

If you want to know the basics of vitamin D, start with Chapter 1. If you have a disease or condition that you think might be affected by vitamin D, check it out in Part II. To make sure you’re getting enough vitamin D, check out Chapter 11 to see how you can get it from the sun, read Chapter 12 for food sources of vitamin D, and flip to Chapter 13 for what you need to know about taking vitamin D supplements.

Part I

The Life History of Vitamin D

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In this part...

In this part, you get an introduction to the basics: what vitamin D is, who needs it, how you measure it, how you get it, and what it does. Because no book on vitamin D is complete without explaining the role of calcium and the other bone minerals, this part also includes a chapter on minerals.

Chapter 1

The Essentials of Vitamin D

In This Chapter

arrow Getting the lowdown on vitamin D

arrow Making the connection between vitamin D and your health

arrow Exploring the origins of vitamin D

arrow Reaping the medical benefits of vitamin D

You think you have enough vitamin D in your body? You’re in for a surprise. You think you know what vitamin D does for you? You’re in for a shock. Many people don’t have enough vitamin D, and almost nobody knows all that it might do for you. In fact, even I don’t know everything it does for you because scientists are discovering new possible roles for it almost daily.

If vitamin D were a house, it might be the most desirable house on the block. It’s turning out to provide possible benefits for your body that you could never have imagined. In this chapter, you discover what vitamin D is and what it does for you.

Understanding What Vitamin D Is and How It Works

When is a vitamin not a vitamin? When it’s vitamin D.

A vitamin is defined as an essential nutrient that a living being must acquire in tiny amounts from the diet. A vitamin is a chemical that’s essential for your body but that your body can’t make; it must be ingested. By this definition, vitamin D isn’t a vitamin at all. Consider this — your skin can make vitamin D when it’s exposed to sunlight, so your body doesn’t have to acquire it from food.

If vitamin D isn’t really a vitamin, what is it? It becomes a hormone called calcitriol (active vitamin D) after your body metabolizes it. A hormone is a chemical in your body that regulates your physiology.

But old names are hard to change, so even though the substance I talk about throughout this book can be made in your skin and becomes a hormone, I (and other experts around the world) still call it vitamin D.

In the following sections, I explain how vitamin D is formed in the skin, how the body turns it into a hormone, and how the vitamin D hormone (calcitriol) affects your body.

Forming vitamin D in the body

Vitamin D comes in two forms:

check.png Vitamin D2: The form found in plants

check.png Vitamin D3: The form found in animals

Both forms of vitamin D are created when the ultraviolet rays of the sun act upon a form of cholesterol. In certain plants, the ultraviolet rays convert a molecule called ergosterol into vitamin D2, which is also called ergocalciferol. In humans, vitamin D starts as a substance in the skin called 7-dehydrocholesterol. The ultraviolet B rays from the sun convert 7-dehydrocholesterol into vitamin D3, or cholecalciferol.

However, neither vitamin D nor vitamin D3 are active yet. In fact, vitamin D does nothing by itself; it’s completely inactive, and that may make you wonder what all the fuss is about. But it’s what vitamin D turns into that becomes important. Vitamin D travels through the bloodstream to the liver, where it’s turned into 25-hydroxycholecalciferol (25(OH)D or calcidiol). This is a prohormone or precursor for the vitamin D hormone. The vitamin D prohormone travels through the bloodstream to the kidneys, where it’s turned into the active form, 1,25-dihydroxycholecalciferol (1,25(OH)2D3 or calcitriol). 1,25(OH)2D3 is the active vitamin D hormone. It is released back into the bloodstream where it then regulates how your body uses calcium and phosphorus. Figure 1-1 shows the conversion process in the body. Figure 1-2 shows the chemical reaction.

Some controversy has arisen over whether vitamin D2 is as active as vitamin D3 when it’s ingested, but the consensus is that D3 is two or three times as potent in raising the level of 25-hydroxycholecalciferol.

9780470891759-fg0101.eps

Figure 1-1: How the body creates vitamin D.

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Figure 1-2: Conversion of 7-dehydrocholesterol to vitamin D3 in the skin.

warning_bomb.epsBecause the liver and the kidneys are involved in the production of calcitriol, diseases of these organs may affect your ability to make this hormone.

Although the kidneys produce most of the calcitriol that ends up in the blood, there is some evidence that the conversion of 25(OH)D3 into 1,25(OH)2D3 may occur in other tissues in the human body. The production of calcitriol in these tissues is low in comparison to the kidney, and calcitriol made in these tissues is probably not released back into the serum. This calcitriol acts within the tissue where it’s made:

check.png Cells of the immune system (macrophages, dendritic cells)

check.png Brain

check.png Breast

check.png Colon (large intestine)

check.png Endothelial cells (inner lining of blood vessels)

check.png Pancreas

check.png Parathyroid glands

check.png Placenta

check.png Prostate

check.png Skin

Remember.epsThroughout this book, when I say “active vitamin D” or calcitriol, I’m referring to 1,25(OH)2D3. It’s easier for your brain to digest “active vitamin D” instead of the string of scientific notation.

Regulating the production of vitamin D

Several factors strictly control the amount of active vitamin D produced in the kidneys and in other tissues. The biggest factor is the result of self-regulation. As the amount of calcitriol increases, it blocks the production of more calcitriol.

Another important substance that stimulates the production of calcitriol is the circulating amount of another hormone called parathyroid hormone. When blood calcium levels fall, parathyroid hormone levels increase and this promotes the conversion of 25(OH)D3 into calcitriol within the kidneys. Concentrations of calcium and phosphate in the blood also control the production of calcitriol by the kidneys even without parathyroid hormone. As the calcium and phosphate levels fall, they stimulate the production of calcitriol in the kidneys.

The production of active vitamin D in organs and tissues other than the kidneys normally doesn’t spill over into the bloodstream to raise the active vitamin D in the blood. For example, during pregnancy the placenta makes calcitriol but at best a negligible amount enters the maternal circulation (pregnant women without kidneys have very low calcitriol levels despite the placenta making calcitriol). However, in certain diseases, such as sarcoidosis (a disease where swelling occurs in the lymph nodes, lungs, liver, skin, and other tissues), immune cells called macrophages produce so much calcitriol that it spills over into the bloodstream and causes increased calcium in the blood.

Moving vitamin D around the body

Vitamin D, 25(OH)D3, and calcitriol are carried in the blood by a vitamin D-binding protein. This protein is necessary because these substances aren’t water soluble and can’t dissolve in blood. (Vitamin D dissolves in fat.) Ninety-nine percent of all the different forms of vitamin D are bound to the vitamin D binding protein, and only 1 percent is free to enter cells.

The different forms of vitamin D that are bound to the vitamin D binding protein are protected from destruction by cells and excretion by the kidneys. Only the 1 percent that’s free is available to carry out the functions of active vitamin D.

Pregnancy and estrogen use are a few conditions that can result in increased production of vitamin D-binding protein. These conditions cause the body to make more active vitamin D to take up all the extra binding sites, but the amount that’s free and able to enter cells usually remains normal. Calcitriol levels more than double during pregnancy but it’s only in the third trimester that free levels of calcitriol increase above normal.

Putting vitamin D to work

The best-understood role for the calcitriol is in the control of how your body uses calcium and phosphorus to make strong bones. However, research is showing that many organs and systems in your body may also need active vitamin D. The intestine and bones rely on the kidneys to make and ship calcitriol to them. However, the other organs that need calcitriol may be able to make small amounts on their own.

Active vitamin D works by entering cells and attaching to a protein called the vitamin D receptor, located in the nucleus of cells, where the genetic material is located. This combination of calcitriol and its receptor stimulates the cell to make proteins that regulate the way the body works. For example, some of the proteins produced in response to calcitriol in the intestine help transport calcium across the intestine and into the bloodstream, greatly increasing the absorption of calcium from the diet. The vitamin D receptor is found in several cells that are critical for controlling the metabolism of calcium, phosphorus, and bone: intestinal cells, bone cells, kidney cells, and parathyroid gland cells.

Vitamin D receptors also are present in most other tissues, including the brain, heart, skin, ovary and testicle, prostate gland, and breast, as well as the cells of the immune system, including white blood cells and other key immune cells (see Chapter 5). In fact, at least 33 different tissues contain the vitamin D receptor:

check.png Adipose (fat)

check.png Adrenal

check.png Bone

check.png Bone marrow

check.png Brain

check.png Breast

check.png Cartilage

check.png Colon (large intestine)

check.png Epididymis

check.png Hair follicle

check.png Kidney

check.png Liver

check.png Lung

check.png Lymphocytes

check.png Muscle, embryonic

check.png Muscle, heart

check.png Muscle, smooth

check.png Osteoblast (bone-forming cell)

check.png Ovary

check.png Pancreas

check.png Parathyroid

check.png Parotid

check.png Pituitary

check.png Placenta

check.png Prostate

check.png Retina

check.png Skin

check.png Small intestine

check.png Stomach

check.png Testis

check.png Thymus

check.png Thyroid

check.png Uterus

Seeing How Vitamin D Affects Your Health

The medical community has known of the benefits of vitamin D on bone health for decades. In more recent years, scientists have discovered that vitamin D may play a role in many other aspects of our health. In the following sections, I give you an overview of some of the most promising areas in which vitamin D may improve health and prevent diseases.

Building bone

The work of calcitriol is intimately linked to the way your body uses calcium. Active vitamin D levels increase when you regularly eat a diet low in calcium. When elevated, the role of calcitriol begins in the intestine, where it promotes increased absorption of calcium in an effort to overcome your low dietary calcium intake. Calcitriol also influences the kidneys, where it keeps calcium from leaving in the urine. Finally in the skeleton, calcitriol causes both the production of the framework of the bone and the mineralization of that framework with calcium and phosphate. On the other hand, abnormally high levels of calcitriol cause bone to break down and too much calcium to be absorbed by the intestines; this can cause toxic levels of blood calcium.

Normal levels of calcitriol promote the breakdown of old bone and the creation of new bone. Another way that calcitriol protects bone is by influencing the production of the parathyroid hormone. If you have a deficiency of vitamin D, you can’t make enough calcitriol. As a result the parathyroid gland makes more parathyroid hormone which goes to bone and breaks it down to release calcium into the bloodstream. If this goes on too long, the increase in parathyroid hormone is detrimental, leading to weakened bones. Restoring vitamin D and calcitriol levels to normal allows the skeleton to regain lost calcium and strength. Maintaining the calcium level in the blood is important for the body’s muscle function: heart muscles, skeletal muscles, and all other muscles. (Check out Chapter 4 for more on bones, teeth, and vitamin D.)

Remember.epsAs they grow, children add more bone than they break down, so bone mass increases. When you’re a kid, calcium absorption from the diet has to be very efficient to meet the needs of growing bone, so active vitamin D is very important at this stage of life. When you stop growing, there is still a lot of activity going on in the bone. About 10 to 30 percent of the bone in your body is renewed each year. After you reach your 30s, you begin to lose slightly more bone than the amount you make, so you have a net loss of bone. At menopause women lose bone mass even more rapidly. Because of all this bone loss during adulthood you need to build up plenty of bone at a younger age so that by the time you start to lose more bone mass than you gain, you can avoid osteoporosis, a condition in which the bones are fragile and can fracture.

Reducing your risk of cancer

One of the most promising new roles for vitamin D is in the prevention of cancer. In some studies, the rates of certain but not all cancers appear to be lower the closer you live to the equator. Some scientists think that this is because you make more vitamin D in your skin the closer you live to the equator. Other studies even show that high blood levels of vitamin D are associated with lower rates of a number of cancers. Based on this they estimate that higher blood vitamin D levels could cause:

check.png A 50 percent reduction in the risk of colon cancer

check.png A 30 percent reduction in the risk of breast cancer

check.png A 30 percent reduction in the risk of ovarian cancer

check.png A 43 percent reduction in the risk of pancreatic cancer

There are some other bits of evidence that suggest this is true. For example, calcitriol has been shown to slow the growth of cancer cells isolated from the breast, the prostate, and the colon, and it can kill cancer cells in culture. (See Chapter 6 for more specifics.) Unfortunately we don’t know if this ability to slow or even kill cancer cells occurs in humans. Also, the high doses of calcitriol needed in cell culture studies would cause toxic, high levels of blood calcium if they were used in humans. Because of this scientists are currently making calcitriol-like drugs that have similar anti-cancer properties in cell cultures as active vitamin D but that avoid the effects of calcitriol on bone and calcium metabolism. That way, doctors could give very high doses of such a compound without risking the toxic side effect of high calcium.

Preventing heart disease and diabetes

Still other studies are pointing to a possible role for high blood vitamin D levels in the prevention of other chronic diseases like diabetes and heart disease. If you looked at a graph comparing the average blood pressure of the population with the distance from the equator, you’d see that blood pressure rises the farther you get from the equator and its strong sun rays (and, therefore, greater skin production of vitamin D). Of course, the change in blood pressure might have nothing to do with vitamin D, but it seems reasonable to assume that it does.

Studies in animals show that calcitriol can lower blood pressure and decrease the risk of an enlarged heart. Calcitriol also relaxes blood vessels, which further lowers blood pressure. (Flip to Chapter 7 for more on how vitamin D helps maintain your cardiovascular system.)

There is also evidence that higher blood vitamin D levels might also protect against the development of diabetes. This might be related to observations that calcitriol can alter the cells of the immune system to suppress autoimmunity, the reaction of the body against itself (see Chapter 5). Type 1 diabetes mellitus is an autoimmune disease, so active vitamin D might help limit the development of this disease. At the same time, studies in animals and cell cultures suggest that calcitriol active vitamin D improves insulin secretion from the pancreas and increases the sensitivity of cells to the action of insulin. These actions might help prevent and treat type 2 diabetes. (Chapter 8 explains the connection between vitamin D and diabetes.)

Checking Out Where Vitamin D Comes From

Outside the body, vitamin D comes from three major sources:

check.png The sun

check.png Food

check.png Supplements

Part III delves into these sources in detail, but I make a few general remarks here.

Sun

The sun has provided vitamin D for thousands of years. However, the sun is also known to cause skin cancer, photo-damage, wrinkles, and other problems. The challenge is striking the right balance between getting enough sun for your vitamin D needs and avoiding sun damage (see Chapter 11 for details). Even still, most dermatologists believe that there is no “safe” level of sunlight exposure and that the sun should not be relied upon as a source of vitamin D.

Four major factors determine the effect of sunlight on your vitamin D level:

check.png Time of year: In the summer, the sun’s rays are more direct. Direct rays much more effectively raise your skin production of vitamin D.

check.png Your latitude on the Earth: Latitudes closer to the equator get direct sunlight for a longer time each day and for more months out of the year.

check.png Obstacles to sun exposure of your skin: Whether it be clouds, dark skin color, smog, a hat, an umbrella, or suntan lotion, anything that limits the exposure of your skin to ultraviolet light significantly reduces your production of vitamin D in the skin.

check.png Altitude: The higher you are, the less atmosphere there is to block the sun’s rays.

Remember.epsAny factor that reduces the amount of ultraviolet light that reaches your skin will reduce the amount of vitamin D produced there.

Food

Only a few foods contain enough vitamin D to make eating them solely for this reason worthwhile. Food manufacturers are fortifying many foods with extra vitamin D. At the present time, vitamin D-fortified foods can provide enough vitamin D only for babies and toddlers, whose requirements are relatively small. In Chapter 12, I tell you what you need to know about foods and vitamin D.

Supplements

With the tremendous growth of knowledge about vitamin D and its effects, there has come an abundance of supplements in every size, shape, and form. If you can’t get enough vitamin D from your diet, you can get all the vitamin D you need from supplements. Chapter 13 tells you how to use pills to meet your vitamin D needs.

Appreciating the Long-Term Medical Benefits

Vitamin D plays a huge role in your health. The most important area in the past has been bone health in children and adults, but many researchers think that vitamin D’s other functions may be equally important.

Prevention of deformity

The major and most well-known role of vitamin D over the years has been preventing rickets in children. When vitamin D isn’t present in sufficient amounts during growth, the bones don’t lengthen properly or become properly mineralized. As a result, the weight of the body makes the bones become curved, deformed, painful, and tender, and they fracture easily — a condition known as rickets. Rickets affects all bones, including the teeth and the spine. Vitamin D is also essential for normal development and maintenance of muscles, and in rickets the muscles are greatly weakened, tender, and sore. (Chapter 4 provides the information you need to avoid rickets.)

When rickets occurs in adults it’s called osteomalacia, and it doesn’t lead to deformity because the bone structure has already formed. It does, however, lead to weak bones and muscles, and pain in muscles and bones that responds to vitamin D.

Rickets was a rare disease until many people began to leave farms and migrate to cities during the Industrial Revolution. The sun didn’t penetrate the pollution as easily, and people stayed indoors most of the day. Nowadays, rickets is still rare in many places; however, it’s making a comeback in racial groups with dark skin and in places where people cover up their skin for religious or social reasons. In fact, some of the lowest vitamin D levels are seen in countries close to the equator where typical outdoor clothing has the head and entire body covered.

warning_bomb.epsUnless the mother takes a very high dose (4,000 to 6,400 IU per day) supplement of vitamin D, human breast milk contains little or no vitamin D. As a result babies who are exclusively breastfed are more likely to become deficient than babies who receive vitamin D-fortified baby formulas. Also, babies born of mothers who were low in vitamin D during pregnancy are even more likely to develop rickets in the weeks to months after birth.

Lives saved?

Some scientists feel that the value of vitamin D in health has been underestimated. However, it’s hard to estimate the effects of vitamin D, for several reasons:

check.png The experts don’t agree on what constitutes “sufficient levels” of vitamin D in your blood.

check.png All of vitamin D’s various contributions to health aren’t fully known.

check.png Controversy exists over whether some of the proposed nonbone effects of vitamin D are real, particularly those effects on chronic diseases that take years to develop, like cancer, heart disease, and diabetes. For example, some studies have shown that a lower intake of vitamin D is associated with a higher risk of heart disease. This could be because the people that took less vitamin D may also have exercised less, smoked more, and had other poor lifestyle habits. A definitive answer requires conducting a study that randomly compares two similar groups — one that gets the vitamin and the other that doesn’t.

Although these randomized studies are very expensive and hard to do, fortunately a large randomized study called VITAL is under way in the USA which is testing the effects of vitamin D on cancer and heart disease outcomes. So we may have a definitive answer to these questions as to whether vitamin D prevents heart disease and cancer in the next five years or so.

In the meantime, by using studies that associate serum vitamin D levels to the risk that a person may develop a disease, and assuming that the low vitamin D is causing the disease of interest, a number of scientists have tried to approximate the number of lives that could be saved by improving vitamin D intake. Using such associational studies, these scientists have come up with some interesting numbers.

They estimate that if Canadians brought their vitamin D levels up to healthy levels (which I outline in Chapter 2), an estimated 37,000 lives a year would be saved.

Scientists proposed that the following benefits would be achieved:

check.png A 25 percent decline in cancer rates

check.png A 25 percent decline in heart disease

check.png A 60 percent improvement in insulin sensitivity, thus protecting against diabetes

check.png Reduction in the risk of multiple sclerosis

check.png A 30 percent reduction in the risk of pneumonia

check.png A 50 percent reduction in Cesarean sections

check.png Complete elimination of rickets and substantial reduction in the rate of osteoporosis

Extrapolating to the United States, which has ten times the population of Canada, more than 300,000 lives a year would be saved by raising vitamin D levels in this country.

Later in the book I discuss just what “healthy” levels of vitamin D might be, and I show you why scientists think that there’s enough evidence to support these numbers.