CHAPTER
9

Vitamins

In This Chapter

  • Distinguishing between water-soluble and fat-soluble vitamins
  • The process of vitamin absorption and digestion
  • B vitamins and their role in the body
  • Getting the right amount of the Recommended Daily Allowance (RDA) for vitamins
  • How to avoid vitamin toxicity

Vitamins are essential for health. Your body is capable of making some of the 13 vitamins needed for it to function properly, but others must be obtained from the foods you eat.

In this chapter, we'll take a look at the important role of each vitamin and how your body uses them to support normal cell function and growth. We will learn how much you need each day and examine which vitamins can be toxic when taken in high doses, along with the detrimental effects in your body.

What Is a Vitamin?

Vitamins are naturally occurring organic compounds that are required by the body for nutrition and growth. These essential micronutrients must be obtained through diet because the body is unable to produce enough of these compounds on its own.

There are 13 vitamins that are classified as either fat-soluble or water-soluble. Fat-soluble vitamins are A, D, E, and K, and they’re stored in the liver or in fatty tissues. The water-soluble vitamins include all of the B vitamins and vitamin C. They’re not stored as long in the body, and the excess is usually released through urine. Therefore, water-soluble vitamins need to be obtained from food sources in your diet every day.

How Vitamins Are Broken Down in the Body

Vitamins are broken down by the mechanical chewing action of your teeth. Food is mixed with saliva and enzymes as you chew. The food is swallowed and transferred from the esophagus to the stomach, where it encounters hydrochloric acid and more enzymes, which aid in the release of nutrients.

The fat-soluble vitamins require the addition of bile so they can be emulsified prior to absorption in the small intestine. Water-soluble vitamins don’t require bile. Once absorbed in the small intestine, the nutrients are released into your bloodstream. The vitamins are next transported to the liver, where one of three things can happen: they’re instantly used by the body, carried to the kidneys to be excreted, or stored in the liver or fatty tissues until the body needs them.

Absorption of vitamins can be disrupted if chronic conditions like alcoholism are present or there’s a disease state within the body. Alcoholism could damage the liver, stomach, and intestines, which are all involved in vitamin absorption and digestion. Intestinal diseases such as Crohn’s disease, irritable bowel syndrome, or any prolonged inflammation of the digestive tract could also interfere with absorption and digestion of vitamins.

Water-Soluble Vitamins

Water-soluble vitamins can be dissolved in water and are not stored in your body. There are nine water-soluble vitamins, including vitamin C and the B vitamins: thiamin (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), pyridoxine (vitamin B6), folate (folic acid), vitamin B12, biotin, and pantothenic acid.

The B Vitamins

The B vitamins are responsible for a variety of processes in the body, such as aiding in energy production from the macronutrients and in the formation of red blood cells. Some B vitamins also function as coenzymes. A deficiency of certain B vitamins can lead to anemia, which causes fatigue and weakness.

B vitamins can be found in proteins like red meat, fish, poultry, eggs, and dairy products. They’re also present in dark-green leafy vegetables, and legumes. Let’s take a more detailed look at each of these vitamins.

DEFINITION

A coenzyme is a molecule that needs an enzyme to initiate or create a chemical reaction.

Vitamin B12

Vitamin B12 is responsible for the health of your body’s nerve and blood cells. It also helps produce DNA and RNA, which are the genetic material found in all cells. Vitamin B12 also works with folic acid to produce red blood cells and regulate iron in your body. Due to vitamin B12’s influence on red blood cells, this vitamin can also aid in prevention of megaloblastic anemia. Megaloblastic anemia is when your body makes blood cells that are very large, structurally abnormal, and immature. This abnormal cell is unable to carry a sufficient amount of oxygen to your body’s tissues.

Your body is unable to produce vitamin B12 on its own, so it must be obtained through the diet. Although certain types of bacteria may produce B12 within the body, the amount is not sufficient to guarantee adequate nutrition.

During the digestion of B12 in the stomach, hydrochloric acid will first separate the vitamin from the protein molecule. Next, in order for B12 to survive the harsh acids in the stomach, it must combine with another protein produced by the stomach known as intrinsic factor. Once bound with intrinsic factor, it can travel on to the small intestine where the intrinsic factor will be degraded. The B12 is absorbed into the bloodstream and is delivered to the liver for distribution.

DEFINITION

Intrinsic factor is an essential glycoprotein that’s produced by the parietal cells within the stomach in order for your body to efficiently absorb vitamin B12. Without intrinsic factor, your body can’t recognize B12.

Without intrinsic factor, you can develop a type of vitamin B12 deficiency called pernicious anemia. Pernicious anemia will lead to megaloblastic anemia. This form of anemia affects red blood cell production by producing fewer cells that are large and immature when compared to healthy red blood cells. This irregularity impacts the cells’ ability to transport oxygen.

Some people don’t make enough intrinsic factor or have a chronic condition that destroys it. Digestive tract disorders such as irritable bowel syndrome (IBS) and Crohn’s disease will cause your body to stop producing intrinsic factor. If the stomach has been surgically removed due to disease or injury, your body will not be able to produce intrinsic factor. Alcoholism, H. pyloric bacterial infections, ulcerative gastritis, Zollinger-Ellison syndrome, gastric bypass surgery, and even age can negatively impact the production of intrinsic factor.

The Recommended Daily Allowance (RDA) for vitamin B12 for adults is 2.4 mcg. The following table lists more detailed information for RDAs. There’s no known toxicity for B12.

DEFINITION

Recommended Dietary Allowance (RDA) is the average daily intake level that meets health requirements for the majority of the population.

Vitamin B12 is found in animal foods, such as meats, poultry, fish, eggs, and dairy. Additionally, vitamin B12 can be found in fortified foods such as cereals.

Vitamin B6

Vitamin B6 has three forms: pyridoxal, pyridoxamine, and pyridoxine. Each type can be used to form nonessential amino acids in metabolism. B6 is involved in hundreds of enzymatic reactions, along with aiding in the body’s immune system and cognitive abilities, as well as production and use of glucose.

Vitamin B6 is digested and absorbed in the jejunum by a process of passive diffusion. Passive diffusion is a way for small molecules to simply diffuse across a membrane.

The RDA for vitamin B6 for adult males and females age 19 to 50 years old is 1.3mg per day. See the following table for more detailed information.

A deficiency of vitamin B6 is uncommon but can cause neurological problems, depression, fatigue, microcytic anemia, skin disorders, and a weakened immune system. Vitamin B6 deficiency can occur when excessive alcohol is consumed, and if you have kidney disease or malabsorption disorders.

The tolerable upper limit (UL) for B6 for adults is 100mg per day. High intake of B6 from food or supplements can cause peripheral neuropathy.

Many foods contain vitamin B6. Sources include fortified cereals, meats, poultry, fish, fruit, and starchy vegetables such as peas and potatoes.

RDA for Vitamin B12 and B6

Age

B12 (mcg)

B6 (mg)

Birth-6 months

0.4

0.1 males/0.1 females

Infants 7-12 months

0.5

0.3 males/0.3 females

Children 1-3 years

0.9

0.5 males/0.5 females

Children 4-8 years

1.2

0.6 males/0.6 females

Children 9-13 years

1.8

1.0 males/1.0 females

Teens 14-18

2.4

1.3 males/1.2 females

Adults

2.4

1.3 males/1.3 females

Adults 51 and over

2.4

1.7 males/1.5 females

Pregnant teens and women

2.6

1.9

Breastfeeding teens and women

2.8

2.0

Thiamin, Riboflavin, and Niacin

Thiamin, or vitamin B1, takes part in a variety of chemical reactions in your body. Thiamin’s primary function is to assist cells in converting carbohydrates into energy. Thiamin also assists with transmission of nerve signals and the contraction of muscles.

The RDA of thiamin for adult males is 1.2mg and for females 1.1mg per day. For more detailed information, refer to the following table. There’s no known toxicity associated with thiamin.

Thiamin deficiency is rare in the United States and is typically associated with alcoholism (Wernicke-Korsakoff syndrome). Symptoms of thiamin deficiency are loss of appetite, weight loss, irregular heart rate, muscle weakness, psychosis, weakness, and nerve damage. Continual thiamin deficiency can lead to a disease called beriberi, which can cause cardiovascular and peripheral nervous system damage. In very severe cases, brain damage can occur.

NOTABLE INSIGHT

Beriberi is caused by a deficiency of B1, and historically it was found in regions where people were dependent on polished rice as a food staple. The polished rice had a longer shelf life, but the process also stripped the thiamin away.

Thiamin can be found in a variety of foods including whole grains, rice, pasta, flour, bread, cereals, beef, pork, eggs, nuts, seeds, legumes, and peas.

Riboflavin, or vitamin B2, is involved in energy metabolism and serves as a coenzyme. These active forms of riboflavin are flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Riboflavin also functions as an antioxidant by protecting the body from free radicals.

The RDA for adult men is 1.3mg per day and for adult women 1.1mg per day. There’s no known toxicity associated with thiamin and no tolerable upper limits have been established. Riboflavin deficiency is very rare and is typically seen in conjunction with other vitamin deficiencies.

Riboflavin can be found in eggs, dairy products, lean proteins, legumes, dark-green leafy vegetables, nuts, and fortified breads and cereals. Riboflavin is also very sensitive to light exposure and is easily destroyed if foods are not kept in dark storage areas.

Niacin, or vitamin B3 is also known as nicotinic acid and nicotinamide (niacinamide). Niacin functions as a coenzyme in the body, where it’s involved in energy metabolism. It also aids in the synthesis of fatty acids and cholesterol. The body can also make niacin from tryptophan.

The RDA for niacin for adult males is 16mg per day and for females 14mg per day. The tolerable upper limit is for adults 35mg per day. Toxicity symptoms are flushing of the skin, hives, nausea and vomiting, and liver damage.

Niacin deficiency was common in the 1800s and was called pellagra, which caused dermatitis, diarrhea, dementia, and eventually death.

Niacin can be found in meats, poultry, fish, eggs, dairy, nuts, and legumes.

RDA for Thiamin, Riboflavin, and Niacin

Biotin, Pantothenic Acid, and Folate

Biotin functions as a coenzyme in the body used in energy metabolism. It’s also involved in the production of glucose and synthesis/breakdown of fatty acids.

There’s no RDA established for biotin, but the Adequate Intake (AI) for adult males is 25 mcg per day and for females 30 mcg. Refer to the following table for more information.

DEFINITION

Adequate Intake (AI) is a value used that is an approximation of required nutrient levels when the Recommended Dietary Allowance (RDA) can’t be determined.

Deficiency of biotin is rare because your body can recycle it. There’s also no known toxicity of biotin.

Biotin can be found in a variety of foods such as egg yolks, liver, fish, and whole grains.

Known as vitamin B5, pantothenic acid forms part of the structure of coenzyme A, which is found in cells. It participates in chemical reactions involved in the release of energy from macronutrients; the synthesis of lipids; hemoglobin, hormones, and neurotransmitters.

There’s no RDA for pantothenic acid, but the AI for adults is 5mg per day. There are no known toxicity levels.

Food sources for pantothenic acid include liver, fish, shellfish, poultry, egg yolks, dairy products, broccoli, legumes, mushrooms, and whole grains. Freezing and canning will reduce its bioavailability.

Folate, folacin, or folic acid is also known as B9 or its chemical name, pteroylglutamic acid (PGA). It functions as a coenzyme in the body. It also helps convert B12 to an active form and aids in synthesis of DNA and new cell formation. It’s digested by enzymes and absorbed in the small intestine. Excess folate is secreted into bile by the liver, and then it’s returned to the gall bladder for storage.

The RDA for adults is 400mcg per day. The tolerable upper limit is established at 1,000mcg per day. There are no known toxicity levels. However, folate supplementation could mask megaloblastic anemia caused by a B12 deficiency. Deficiency of folate can lead to megaloblastic anemia. It can also cause neural tube birth defects such as spina bifida.

NOTABLE INSIGHT

Neural tube defects affect the brain, spine, or spinal cord in a fetus, and occur during the first month of pregnancy. An adequate intake of folic acid prior to pregnancy can prevent most cases.

Folate can be found in a variety of foods like green leafy vegetables, legumes, citrus fruits, and fortified foods such as breads, cereals, pasta, and rice.

AI for Biotin, Pantothenic Acid, and RDA for Folate

Vitamin C

Vitamin C is a water-soluble vitamin and is sometimes called ascorbic acid. Its role in the body is to function as an antioxidant, aid in the production of collagen, and support your immune system. As an antioxidant, it works in the body by protecting against free radicals that damage cells. Free radicals are byproducts of normal metabolism, but they also come from outside sources such as pollution, cigarette smoke, and exposure to UV light.

When your body is physically stressed due to the presence of an infection or serious injury, adrenal glands release vitamin C to support immune functions. Vitamin C ensures that the oxidative process involving free radical release runs smoothly.

Vitamin C helps make collagen, which is a fibrous protein used in building bones and teeth. It also helps strengthen veins and capillary walls, along with aiding in wound repair. It supports collagen formation by protecting iron molecules from being oxidized during the formation of collagen. Without vitamin C’s action, no protein would be formed and tissue repair, such as in the formation of scars, would never occur.

FOODIE FACTOID

British sailors were called “limeys” because they carried limes on their voyages to prevent the vitamin C deficiency disease called scurvy.

Deficiency of vitamin C is rare in the United States, as you would have to consume less than 10mg over several weeks to develop scurvy. One orange provides 70mg of vitamin C.

The RDA for vitamin C is provided in the following table. If you’re a smoker, add 35mg daily.

RDA for vitamin C

Age

Recommended amount in milligrams (mg)

Birth-6 months

40

Infants 7-12 months

50

Children 1-3 years

15

Children 4-8 years

25

Children 9-13 years

45

Teens 14-18 years (boys)

75

Teens 14-18 years (girls)

65

Adult males

90

Adult females

75

Pregnant teens and women

80 (pregnant teens)85 (pregnant adult women)

Breastfeeding teens and women

115 (breastfeeding teens)120 (breastfeeding adult women)

Vitamin C can be found in a variety of fruits and vegetables. We typically look to citrus fruits such as oranges and grapefruits, but bell peppers, broccoli, and tomatoes are also good sources.

The tolerable upper intake limit for Vitamin C for adults is 200mg per day. If you overconsume vitamin C, it can lead to headache, nausea, diarrhea, stomach cramps, fatigue, and hot flashes. However, you would have to take an excess of over 4,000 mg per day.

Fat-Soluble Vitamins

The fat-soluble vitamins are A, D, E, and K. These vitamins provide a variety of functions in the body: keeping your eyes healthy, strengthening your bones, protecting your cells, and clotting blood. Because these vitamins are fat-soluble, they must be emulsified by bile before your body can absorb them. Additionally, many need a protein carrier to travel through the bloodstream. Unlike water-soluble vitamins, fat-soluble vitamins can be stored in the liver and fatty body tissues, which allows your body to release the vitamins on demand. It also means you don’t necessarily need to eat foods containing that particular vitamin every day because your body can store it. Unfortunately, with A, D and E, you can reach toxic levels that can be detrimental to your health.

Vitamin A

There are three forms of vitamin A. One type (retinol) is from animal sources and is also referred to as preformed vitamin A. The other two, retinal and retinoic acid (alpha carotene and beta-carotene) are from plant sources and are also known as provitamin A. Vitamin A performs many functions in the body. It helps promote normal vision and the growth of healthy cells, regulates the immune system, and is important for embryo development.

Vitamin A supports your vision by keeping the cornea of the eye healthy. It also helps you see in the dark by aiding in the chemical reaction within the eye that has to do with the absorption of wavelengths of light.

Vitamin A plays an important role when it comes to cellular growth and division in the body. This vitamin aids in protein synthesis and cell differentiation, which means each cell is told what job it will perform, ranging from being a skin cell on the outside of your body to being a mucous cell on the inside of your body lining the GI tract.

Vitamin A is important in the reproductive cycle for men and women. In men, the vitamin helps sperm development. In women, it aids in fetal development.

The RDA for adult males is 900mcg retinol activity equivalents (RAE) per day and for women 700mcg. RAE is a unit of measure and refers to the body’s ability to convert provitamin carotenoids into vitamin A. For more detailed information, refer to the table at the end of this section.

FOODIE FACTOID

Carrots are a good source of beta-carotene. Americans consume just over 10 pounds per person each year.

Deficiencies of vitamin A are rare in the United States. However, it’s the leading cause of blindness in developing countries. Deficiency symptoms are corneal drying, which leads to blindness, impaired immunity, and plugged hair follicles that cause white bumps to appear on the skin, referred to as hyperkeratosis.

Since vitamin A can be stored in the body, it’s possible to reach toxic levels. The tolerable upper limit for adults 19 and older is 3,000mcg per day. Toxicity can cause birth defects, reduced bone density, blurred vision, vertigo, headaches, and abnormal muscle function.

It’s easy to get plenty of vitamin A from foods, such as eggs, liver, spinach, broccoli, vitamin A-fortified dairy products, and orange-colored fruits and vegetables such as apricots, winter squashes, carrots, and sweet potatoes.

Vitamin D

The primary function of vitamin D is to help make strong bones by aiding in the body’s ability to absorb calcium. It also supports neurotransmissions and strengthens the immune system.

Vitamin D is also known as calciferol and is technically a hormone. Your body can make vitamin D from exposure to sunlight. A chemical compound of vitamin D is made from cholesterol in your liver. The liver releases this compound, which then travels to the skin and the ultraviolet light from the sun changes the molecule into previtamin D3, an inactive form. It then travels to the liver where the molecule is changed into 25-hydroxy vitamin D3, and then moves into the kidneys where it is converted into the active form vitamin D3 (1,25-dihydroxy vitamin D3). Therefore, if you receive regular sunlight exposure, there is no need to consume food sources of vitamin D.

Vitamin D helps support bone growth by maintaining a tight control on blood levels of calcium and other minerals such as phosphorus, magnesium, and fluoride. This vitamin can direct the body to absorb more calcium in the GI tract or pull it from the bones. It works in conjunction with the kidneys and other hormones to ensure there’s an adequate supply of minerals in the blood.

Recommended intake for adults 19-70 years old is 600IU. Refer to the table at the end of this section for more detailed information.

Vitamin D deficiency disease is rare in the United States. When there are insufficient amounts of vitamin D in the body, the bones don’t calcify properly and it causes the leg bones to bow outwards in children. Known as rickets, this occurs because the bones are too weak to support the weight of the child, and is why dairy products are fortified with vitamin D. Rickets also causes beaded ribs, which are malformations between the attachment of bone and cartilage.

Additional symptoms are bone pain and low levels of calcium in the blood. In adults a vitamin D deficiency can cause soft bones, a condition called osteomalacia. Kidney disease is also a factor that could lead to a vitamin D deficiency since it’s so closely tied to the production of vitamin D.

Excess consumption of vitamin D can lead to toxicity. It will cause too much calcium to be released into the blood where it can harden blood vessels and arteries. It can also cause the formation of kidney stones.

NOTABLE INSIGHT

To get your daily dose of vitamin D from the sun, you need 15 minutes of exposure.

Sources of vitamin D in the diet are fortified-food products, such as dairy, along with egg yolks, liver, fatty fish, veal, and beef.

Vitamin E

Vitamin E is also known as tocopherol. Scientists actually discovered multiple forms of tocopherol, but only one is active in the body. Its primary function is to work as an antioxidant to protect cells from damage by free radicals. Vitamin E also prevents oxidation of LDL cholesterol, and it aids in the formation of red blood cells and maintains stores of vitamins A, K, iron, and selenium.

Recommended vitamin E intake for in adults is 15mg. Refer to the table at the end of this section for more detailed information.

Vitamin E deficiency is rare and typically linked to a fat malabsorption disease. Without adequate amounts of vitamin E, nerve and muscle damage can occur, including muscle weakness and loss of feeling in the extremities, along with impaired vision and an immune system.

Consumption of excess amounts of vitamin E from dietary sources is not toxic. However, additional intake from supplements may affect the body’s ability to clot blood. The tolerable upper limit is 1,000mg per day.

Vitamin E can be found in vegetable oils, nuts, spinach, broccoli, and fortified foods like breakfast cereals and margarine.

Vitamin K

There are actually many compounds that make up what we refer to as Vitamin K. Phylloguinone is a natural form of vitamin K found in green plants, and menaquinones are a natural form made by bacteria. Menadione is a synthetic form of vitamin K that can be converted by enzymes to an active form in the body.

Vitamin K’s function in the body is to assist in the role of blood clotting. It also aids in bone formation by helping calcium bind to the protein matrix in the structure of bones.

Recommended daily intake for adult males is 120mcg and for females 90mcg. Refer to the table at the end of this section for more detailed information.

Deficiency of vitamin K can lead to hemorrhaging, but it’s rare. Newborn babies are dosed with vitamin K because vitamin K doesn’t pass through the placenta, and they also don’t have sufficient gut bacteria to produce it on their own.

There’s no known toxicity associated with natural forms of vitamin K and thus the Food and Nutrition Board of the Institute of Medicine has established no tolerable upper limits. However, large amounts of the synthetic form could cause liver damage.

WAKE-UP CALL

Do not consume foods high in vitamin K if you’re on a blood thinner like Coumadin. Vitamin K can adversely interact with the medication.

Food sources of vitamin K are leafy greens, broccoli, cauliflower, liver, fermented dairy and soy products, wheat bran, and green tea.

RDA for vitamins A and E, AIs for vitamins D and K

The Least You Need to Know

  • Fat-soluble vitamins are stored in the body’s tissues. It’s best not to take excessive amounts in supplement form.
  • Water-soluble vitamins aren’t stored in the body and need to be consumed daily in your diet.
  • Inadequate intake of B6 and B12 can lead to anemia, which causes fatigue and weakness.
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