Riboflavin Vitamin B

What Is Riboflavin?

Riboflavin has long been called vitamin B2 and is a B-complex vitamin meaning that it plays a key role in energy metabolism. The name riboflavin refers both to a component of its molecular structure and also its yellow color: ribo- with respect to the ribose (a simple sugar) portion of the molecule and flavin from the Latin word for yellow, flavus.

What Foods Have Riboflavin?

Sources of riboflavin include rapidly growing, green leafy vegetables, beef liver, beef, and dairy products (Table 9.4). About one-fourth to one-half of the riboflavin Americans consume is provided by milk and milk products. Meats are also a primary supplier of dietary riboflavin along with fortified and enriched foods (breads and breakfast cereals, for example).

Is Riboflavin Stable During Cooking and Storage?

Riboflavin appears to be more stable than vitamin C and thiamin with regard to cooking and storage. However, significant riboflavin losses in foods are experienced when foods are exposed directly to light (for example, sunlight). This was a bigger concern back when milk was packaged in clear glass bottles and delivered to your doorstep usually before people got out of bed. The milk would then be exposed to the morning sunlight until it was brought in the house. As most milk producers no longer package their product in clear containers such as glass bottles this helps milk retain most of its riboflavin. Sun drying and cooking foods in an open pot can lead to significant riboflavin losses as well. Furthermore, like other water-soluble vitamins, riboflavin can be washed away during boiling and thawing (thaw drip).

Table 9.4 Riboflavin Content of Select Foods







Milk and milk products


Milk, whole (1 cup)


Liver (3 ounces)


Milk, 2% (1 cup)


Pork chop (3 ounces)


Yogurt, low-fat (1 cup)


Beef (3 ounces)


Milk, skim (1 cup)


Tuna (3 ounces)


Yogurt (1 cup)



Cheese, american (1 ounce)


Collard greens (% cup)


Cheese, cheddar (1 ounce)


Broccoli (% cup)



Spinach, cooked (% cup)


Macaroni (% cup)



Bread (1 slice)


Egg (1)


202 Vitamins Are Vital Molecules in Food How Much Riboflavin Do We Need?

The RDA for adults is 1.1 to 1.3 milligrams of riboflavin for adult women and men. Meanwhile the RDA for pregnant and lactating women is 1.4 and 1.6 milligrams respectively. Because riboflavin is important in energy operations it might be more appropriate to express recommendations for more athletic people based on level of additional calories burned during exercise and sport training/competition. Here, 0.6 grams of riboflavin would be recommended for every 1,000 calories expended daily. Thus athletes expending 3,000 to 6,000 calories daily would have a recommendation of 1.8 and 3.6 milligrams. See Table 3.2 for recommended levels for children and teens.

Where Is Riboflavin in Our Body?

Riboflavin in foods is well absorbed from our digestive tract. Although riboflavin is found in most cells in the body, higher concentrations will be found in very active tissue, such as the heart, liver, and kidneys. This makes sense due to riboflavin's heavy involvement with aerobic energy metabolism. Riboflavin status is typically assessed by taking a sample of blood and assessing the activity of process that requires riboflavin to operate efficiently. Because of its water solubility, riboflavin is lost from the body in urine, which is visually obvious as urine turns a bright yellow a short time after ingesting riboflavin supplements.

What Does Riboflavin Do in the Body?

Riboflavin functions in the cells as an essential component of two coenzymes, FAD and FMN, which are often referred to as flavins. With regard to energy metabolism, FAD (flavin adenine dinucleotide) serves as one of the electron carriers mentioned in our discussion of aerobic energy metabolism in Chapter 8. FAD transfers electrons from reactions in the Krebs' cycle and also the breakdown of fatty acids, a pathway that researchers call p-oxidation (see Figure 9.1).

Riboflavin is involved in several operations that help convert food and stored energy to ATP to power cell activities.

FMN (flavin mononucleotide), on the other hand, also functions in electron transfer as a key component of the electron-transport chain in the mitochondria in our cells. Beyond energy metabolism, FAD and FMN are used in many of our cell systems such as amino acid and steroid hormone metabolism. As you might have guessed, these and other riboflavin-requiring cell activities involve the transfer of electrons from one molecule to another. That is what riboflavin-based co-enzymes do: they transfer electrons.

What Happens If Too Little or Too Much Riboflavin Is Consumed?

Deficiency of riboflavin rarely occurs by itself. However, if a diet contains very little riboflavin, a person would begin to show deficiency signs after a couple of months, such as inflammation of the mouth and tongue. Other signs of riboflavin deficiency include dryness and cracking at the corners of the mouth, lesions on the lips, accumulation of fluid in tissue (edema), anemia, and neurological disorders, as well as mental confusion. On the other hand, there does not appear to be great concern regarding riboflavin toxicity because of its rapid removal from the body in urine.

Niacin (Vitamin B3)

What Is Niacin?

Niacin is more commonly recognized as vitamin B3 and is part of the B-complex vitamins. Niacin in its two forms, nicotinic acid and nico-tinamide, is active in the body as part of co-enzyme structures that participate in many bodily activities. In addition to niacin's fundamental role in nutrition, higher levels of niacin can be used therapeutically to lower blood cholesterol levels.

What Foods Contain Niacin and What Is the Supplemented Form?

Niacin is found well distributed throughout most foods. Brewer's yeast and most fish, pork, beef, poultry, mushrooms, and potatoes offer higher niacin content (Table 9.5). Niacin in foods appears to be stable in most forms of cooking and storage while some losses may occur during the boiling of foods as well as during the thaw drip. In these cases some niacin can dissolve into the water that eventually is drained from the food. Both nicotinamide or nicotinic acid can be used in formulating nutrition supplements, however nicotinamide is the form typically used as well as in food fortification.

How Much Niacin Do We Need?

The adult RDA is 14 and 16 mg or niacin equivalents (NE) for women and men respectively, to prevent deficiency and provide for good status. During pregnancy and lactation the recommendation increases for

Table 9.5 Niacin Content of Select Foods









Liver (3 ounces)


Asparagus (% cup)


Tuna (3 ounces)



Turkey (3 ounces)


Wheat germ (1 ounce)


Chicken (3 ounces)


Rice, brown (% cup)


Salmon (3 ounces)


Noodles, enriched (% cup)


Veal (3 ounces)


Rice, white, enriched (% cup)


Beef, round steak (3 ounces)


Bread, enriched (1 slice)


Pork (3 ounces)


Milk and milk products:

Haddock (3 ounces)


Milk (1 cup)


Scallops (3 ounces)


Cheese, cottage (% cup)


Nuts and Seeds

Peanuts (1 ounce)


Note: Niacin recommendations are often stated in niacin equivalents (NE) whereby 1 NE = 1 mg of niacin = 60 mg tryptophan.

Note: Niacin recommendations are often stated in niacin equivalents (NE) whereby 1 NE = 1 mg of niacin = 60 mg tryptophan.

women to 18 and 17 mg respectively. Because niacin is important in energy operations it is more appropriate to express recommendations for more athletic people based on level of additional calories burned during exercise and sport training/competition. Here, 6.6 grams of niacin would be recommended for every 1,000 calories expended daily. Thus athletes expending 3,000 to 5,000 calories daily would have a recommendation of 20 to 35 milligrams. See Table 3.2 for recommended levels for children and teens.

Where Is Niacin Found in Our Body?

The niacin in foods is well absorbed from our small intestine and is found in all of our cells. Like riboflavin we can expect to find higher concentrations of niacin in more metabolically active tissue, or those tissues with higher energy demands such as the heart, brain, liver, and skeletal muscle. Niacin will be lost from the body mostly as part of our urine.

What Does Niacin Do in the Body?

Like riboflavin, niacin imparts coenzyme activity to our cells. In fact, hundreds of chemical reactions depend upon niacin to proceed. Like ribo-flavin in the form of FAD, niacin in the form of NAD (nicotinamide dinucleotide) is a carrier of electrons from energy pathways to the electron-transport chain during aerobic energy metabolism (see Figure 9.1).

Niacin is involved in energy-generating processes in the body as well as the production of cholesterol and fat.

Niacin is also part of another electron-transferring molecule called NADP (nicotinamide dinucleotide phosphate). NADP also transfers electrons between molecules and is vitally important in making cholesterol and fatty acids.

Can We Make Niacin in Our Body?

Some niacin can be made in the body starting with the essential amino acid tryptophan. However, the conversion is very inefficient and it requires about 60 milligrams of tryptophan to produce 1 milligram of niacin. Since daily niacin needs are 13 to 20 milligrams for adults, it is unrealistic to rely upon the conversion of tryptophan to niacin, especially since tryp-tophan is not one of the most abundant amino acids in our diet and serves critical roles beyond protein production. Nevertheless, since some niacin can be made from tryptophan, the RDA is stated as niacin equivalents (NE) where 1 NE is equal to 1 milligram of niacin or 60 milligrams of tryptophan.

What Happens If Too Much Niacin Is Consumed?

Ingesting more than 100 milligrams of niacin as nicotinic acid can result in an uncomfortable feeling. Headache and itching are common, accompanied by an increased blood flow to our skin ("flushing"). On the other hand, physicians often prescribe niacin (2 to 5 grams/day) as a means of reducing blood cholesterol. Because gram doses of niacin can have a pharmaceutical effect, this practice is not suggested unless under medical supervision. Furthermore a tolerable upper limit is set at 35 milligrams/day.

What Happens in Niacin Deficiency?

Based on the many roles of niacin in energy processes, poor niacin status can reduce the efficiency of energy systems. Some of the earlier symptoms of a niacin deficiency include a decreased appetite, weight loss, and a general feeling of weakness. More severe niacin deficiency can result in a severe disease syndrome called pellagra, which is characterized by the three "D's" (dermatitis, diarrhea, dementia) possibly leading to the fourth "D" (death).

206 Vitamins Are Vital Molecules in Food Biotin

What Is Biotin?

Biotin is a B-complex vitamin based on its basic role in energy metabolism. However, because biotin deficiency has been associated with hair (fur) loss in animal studies, it is often marketed in products to improve hair.

What Foods Contain Biotin and What Forms are Used in Supplements?

Biotin is widely dispersed throughout the foods we eat, although its concentration is somewhat limited. Liver, oatmeal, almonds, roasted peanuts, wheat bran, brewer's yeast, and molasses are good sources. While milk and milk products contain only mediocre amounts of biotin, they actually are some of the best providers of biotin in our diet because of their popularity. Eggs offer a respectable amount of biotin, however, egg whites contain a protein called avidin that will bind to biotin in our digestive tract and decrease its absorption. Fortunately, avidin's ability to bind biotin is diminished when eggs, or their whites, are cooked. In addition to preventing salmonella infection, this is another reason to avoid uncooked eggs (or egg whites) as well as egg-based products that have not been pasteurized.

Can Some Biotin Be Made in Our Body?

The bacteria living in the colon can produce biotin, and some of this biotin can be absorbed. This seems to make a respectable contribution toward meeting our biotin needs, however it is not enough to be relied upon exclusively. Furthermore, since it is bacterial cells and not our own cells that make biotin, it should not really be viewed as a vitamin that the human body can make. Therefore, biotin indisputably maintains its place on the list of vitamins.

How Much Biotin Do We Need?

The AI for biotin for adults is 30 micrograms daily. The recommendation remains the same during pregnancy and is increased to 35 micrograms during lactation. Because biotin is important in energy operations it is extremely important that more active people get at least the recommended level and perhaps more appropriately 50 to 60 micrograms daily. See Table 3.2 for recommended levels for children and teens.

Vitamins Are Vital Molecules in Food 207 What Does Biotin Do in Our Body?

Similar to thiamin, riboflavin, and niacin, biotin also provides vital assistance to energy operations and is found in higher concentrations in the brain, muscle, and liver. Serving as a coenzyme, biotin is pivotal in making glucose from other substances such as amino acids and lactate to help maintain blood glucose levels during fasting and prolonged exercise. Biotin is also necessary to make fatty acids from excessive glucose and certain amino acids. Lastly, biotin is necessary for the pathways that help break down certain fatty acids (odd-chain length) and amino acids for energy.

Can Too Much or Too Little Biotin Be Consumed?

Because biotin is widely available in foods and is also derived from the bacteria in our intestinal tract, deficiency is very uncommon. However, some of the rare cases of biotin deficiency include hospital patients fed a biotin-deficient solution intravenously (IV) or in infants fed a lot of egg whites as a protein supplement. On the other hand, biotin seems to be relatively nontoxic.

Boost Your Metabolism and Burn Fat

Boost Your Metabolism and Burn Fat

Metabolism. There isn’t perhaps a more frequently used word in the weight loss (and weight gain) vocabulary than this. Indeed, it’s not uncommon to overhear people talking about their struggles or triumphs over the holiday bulge or love handles in terms of whether their metabolism is working, or not.

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