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These compounds are the stars of the nutrition world, and it was their discovery, probably more than anything else, that fueled the explosion of research into human nutrition.

The current list of vitamins, thirteen to be exact, have been known to be essential for human life for several decades. However, scientists continue to study these intriguing nutrients to learn more about them—everything from how the body absorbs them from different foods to possible interactions within the body's cells. One thing is certain: as new facts unfold, new questions arise.

What Are Vitamins?
For a substance to be added to the highly dignified list of vitamins, it must be recognized as an essential player in at least one necessary chemical reaction or process in the body. Vitamins are non-caloric substances and are required in very small amounts, typically micrograms (μg) to milligram (mg) quantities. A microgram and a milligram are one-millionth and one-thousandth of a gram, respectively. Vitamins either can’t be made in the body or are not made in sufficient quantities to meet our needs. We will discuss two vitamins (niacin and vitamin D) that can be made in the body, and two others (vitamin K and biotin) that are made by the bacteria inhabiting the large intestine. However, they are still considered vitamins, which will be explained shortly.

Although nutrition researchers still study vitamins to learn about what they do, we know some of their general roles. Some act like hormones in the body, sort of chemical messengers. Others are a part of enzymes, vital compounds that control metabolic reactions in the body. Many of the enzymes vitamins team up with can't function unless they combine with specific vitamins, called coenzymes. A useful way to sort vitamins is into two groups: those that dissolve in fat (fat soluble) and those that dissolve in water (water soluble). This gives you some idea of how the vitamins function and how they're handled by the body. In addition, solubility determines if a vitamin can be stored in the body and how easily it's lost from the body as well as from foods during processing or preparation. And finally, knowing whether a vitamin dissolves in fat or water can give you a rough idea of which foods contain it.

vitamins_capsuleYou don't need much of any of the vitamins—it works out to about an ounce if you add up all the vitamins you need for a day. But scientists use different units of measure for vitamins, including mg and micrograms. Just to get an idea of how little a microgram is, one of these tiny units is equivalent to one-millionth of a gram, and a gram is about one-thirtieth of an ounce! Retinol equivalents (RE), and sometimes International Units (IU), are the measurements used in industry for vitamins A and E. Since there are thirteen essential vitamins (fourteen, if you count the newcomer choline), our sample meal would get a bit complicated, so we'll look at two key vitamins that many Americans don't get enough of: vitamins A and C. What you'll notice is that with few exceptions, most of the significant sources of both vitamins are fruits and vegetables. One important distinction is that even in these foods, there is a wide variability in the amounts—notice that a banana and an apple provide negligible amounts of either nutrient. But the sample meal is perfectly balanced and provides our reference female with almost four times the recommended amount of vitamin A and more than seven times the vitamin C.

Vitamins have specialized duties in the body, but many share similar types of functions. Some vitamins serve as chemical messengers, similar to hormones. Although the term hormone evokes colorful images of overpowering passions, hormones control the body's internal environment by keeping the innumerable activities of cells and organs in check. The process starts when specialized groups of cells, or organs such as the pancreas, release hormones in response to a situation in the body which needs correcting. The hormone travels in the blood away from its point of origin to the target, again a group of cells or an organ, and tells the target to do something.

The easiest example to understand is that of the hormone insulin, which the pancreas releases in response to an increase in blood sugar or glucose level, such as occurs after a meal. Insulin courses through the blood and relays the message “clear glucose from the blood.” This simple message causes a variety of tissues to respond in different ways, but all with the goal of reducing blood glucose. To fat cells, whose purpose is to store excess glucose as fat, the reaction is to do just that. In contrast, other cells respond by allowing glucose to enter and perhaps be used for energy, and liver cells take up the glucose and make glycogen, a storage form of the sugar, for later use. The result is that in short order, the blood glucose level returns to normal.



- Vitamin A (retinol)
- Vitamin Bp (choline)
- Vitamin B1 (thiamin)
- Vitamin B2 (riboflavin, vitamin G)
- Vitamin B3 (niacin, vitamin P, vitamin PP)
- Vitamin B5 (pantothenic acid)
- Vitamin B6 (pyridoxine, pyridoxamine, or pyridoxal)
- Vitamin B7 (biotin, vitamin H)
- Vitamin B9 (folic acid, folate, vitamin M)
- Vitamin B12 (cobalamin)
- Vitamin C (ascorbic acid)
- Vitamin D (ergocalciferol, or cholecalciferol)
- Vitamin E (tocopherol)
- Vitamin K (naphthoquinoids)

For an example in the vitamin family, we turn to vitamin D, which some scientists say is more properly termed a hormone. While vitamin D has an active role in bone formation, one indirect way in which it fulfills this role is to regulate calcium levels in the blood. As with most compounds in the blood, the level of calcium must remain within a narrow range. If it doesn't stay in the right range, horrific results could ensue such as tetany, a condition marked by convulsions and muscle spasms. Vitamin D acts as a hormone by telling bone tissue to give up some calcium and release it into the blood in order to raise blood calcium levels.

There are 13 vitamins in all, and you need every single one of them, no exceptions. Vitamins aren't food or a substitute for food. They have no calories and give you no energy directly—but your body needs vitamins, especially the B vitamins, to convert food to energy. We'll look at each vitamin in detail in the later chapters of this book, but for now we'll divide them into two groups: fat-soluble and water-soluble.

Fat-Soluble Vitamins

Fat-soluble vitamins are stored in your body, mostly in your fatty tissues and in your liver. Vitamins A, E, D and K are fat-soluble—that is, they dissolve in fat but not water. Because you can store these vitamins, you don't have to get a supply of them every day. On the other hand, getting too much of these vitamins means they could build up in your body and cause problems.

Fat-soluble vitamins are very dependent upon the processes of normal lipid digestion and absorption, such as the presence of bile and the construction of chylomicrons in the cells lining our small intestine. Thus, any situation in which there is decreased bile production and/or delivery to our small intestine would greatly decrease fat-soluble vitamin absorption into our body. Because the presence of fat in the diet is the most powerful stimulus for bile delivery to the small intestine, it only makes sense that a nutrition supplement containing fat-soluble vitamins should be taken with a fat-containing food or meal.

Water-Soluble Vitamins

Water-soluble vitamins can't really be stored in your body for very long. That's because these vitamins dissolve in water, so any extra is carried out of your body. Vitamin C and all the B vitamins are water-soluble. Because you can't store these vitamins, you need to get a fresh supply every day. You can't really overdose on water-soluble vitamins. Unless you take truly massive doses, the extra just washes harmlessly out.

The water-soluble vitamins include the B-complex vitamins and vitamins C and choline. DRI recommendations for water-soluble vitamin intake is in the range of micrograms to milligrams. In addition to foods, supplements make a significant contribution to many people’s intake.

Vitamin Links to Preventing Specific Diseases
Fat Soluble Vitamins
Vitamin A protection against ulcers, epithelial tissue cancers; carotenoid precursors: heart disease, cancer
Vitamin D protection against osteoporosis, colon cancer, diabetes, osteoarthritis
Vitamin E protection against cancer, heart disease, cataracts, Alzheimer's disease, colon cancer

Water Soluble Vitamins
Niacin lowers blood cholesterol
Vitamin B6/Pyridoxine protection against heart disease, premenstrual syndrome, carpal tunnel syndrome
Folate protection against heart disease, neural tube defects
Vitamin B12/Cobalamine protection against heart disease
Vitamin C/Ascorbic Acid protection against cancer, heart disease, cataracts

How Much Do You Need?
How much you need of each vitamin is a question that has a lot of different answers, depending on who you are and who you ask. For now, we're going to tell you what the doctors and scientists at the Food and Nutrition Board of the Institute of Medicine think is enough to meet your basic needs for each vitamin, assuming you're an average healthy adult man or woman. The Institute of Medicine
is the group that brings you the Recommended Dietary Allowances, better known as RDAs. These are the minimum amounts you should be getting every day, preferably from your food (and from vitamin pills if you need to).

Adult RDAs for Vitamins

Vitamin RDA for Men

RDA for Women

Vitamin A 1,000 RE or 5,000 IU 800 RE or 4,000 IU
Vitamin D 5 mcg or 200 IU 5 mcg or 200 IU
Vitamin E 10 mg or 15 IU 8 mg or 12 IU
Vitamin K 80 mcg 65 mcg
Vitamin C 60 mg 60 mg
B Vitamins:    
Thiamin 1.5 mg 1.1 mg
Riboflavin 1.7 mg 1.3 mg
Niacin 19 mg 15 mg


Folic acid


2.0 mg

200 mcg

2.0 mcg

1.6 mg

180 mcg

2.0 mcg



Disclaimer: This website is for information purposes only. By providing the information contained herein we are not diagnosing, treating, curing, mitigating, or preventing any type of disease or medical condition. Before beginning any type of natural, integrative or conventional treatment regime, it is advisible to seek the advice of a licensed healthcare professional.

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