- Email: [email protected]
Vitamins | Riboflavin
Riboflavin D Nohr and H K Biesalski, Universita¨t Hohenheim, Stuttgart, Germany E I Back, Novartis Pharma GmbH, Nu¨rnberg, Germany ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by H. K. Biesalski and E. I. Back, Volume 4, pp 2694–2699, ª 2002, Elsevier Ltd.
Riboflavin or Vitamin B2 The chemical name for riboflavin is 7,8-dimethyl-10-(19D-ribityl)isoalloxazine; riboflavin exists in an oxidized and a reduced form (Figure 1), from which two coenzymes are formed: flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD; Figure 2). The ending ‘flavin’ refers to its yellowish color (in Latin flavus means yellow). Free as well as protein-bound riboflavin occurs in the diet, and milk in general is the best source. In cow’s milk, the free form, with a higher bioavailability, is the major one (61% riboflavin, 26% FAD, 11% hydroxyethyl form, and others), whereas the protein-bound, and thus less bioavailable, form predominates in other foods. In human breast milk, approximately one- to two-thirds of riboflavin occurs as FAD. Riboflavin is very heat stable but it is extremely photosensitive. It is photodegraded to lumiflavin (under alkaline conditions) or lumichrome (under acidic conditions), both of which are biologically inactive. Concentrations are significantly reduced in high-pressure low-temperature treated milk as compared to raw milk. UV light excites riboflavin to a high degree of natural fluorescence, which is used for its detection and determination in yogurt or non-fat dry milk.
Functions of Riboflavin Riboflavin-dependent enzymes are called flavoproteins or flavoenzymes, because of their yellowish appearance. They catalyze hydroxylations, oxidative decarboxylations, dioxygenations, and reduction of oxygen to hydrogen peroxide, serving as electron carriers, mediators of electron transfer from pyridine nucleotides to cytochrome c or to other one-electron acceptors, and as catalysts of electron transfer from a metabolite to molecular oxygen. The two flavoenzymes, FMN and FAD, play major roles in the metabolism of glucose, fatty acids, amino acids, purines, drugs and steroids, folic acid, pyridoxine, vitamin K, niacin, and vitamin D.
704
The FAD-dependent enzyme, glutathione reductase, plays a major role in the antioxidant system by restoring reduced glutathione (GSH) from oxidized glutathione (GSSH). GSH is important in protecting lipids from peroxidation and in stabilizing the structure and function of red blood cells; it is the most important antioxidant in erythrocytes and in keeping lens proteins in solution (thus preventing cataracts). The formation of FMN and FAD is ATP dependent and takes place mainly in the liver, kidney, and heart. All enzymatic steps are under the control of thyroid hormones. riboflavin þ ATP ! r/FMN þ ADP • Flavokinase: FAD pyrophosphorylase: þ ATP ! /FAD þ PP • FAD þ apoenzyme/proteinFMN ! covalently bound flavins •
Sources of Riboflavin Tables 1 and 2 summarize dietary sources of riboflavin and its concentration, especially in the milk of various species and in dairy products. Heat treatment has only negligible effects on riboflavin concentrations, whereas exposure of milk to sunlight results in the loss of 20–80% of riboflavin. Thus, storage in dark bottles, light-tight wax cartons, or special polyethylene terephthalate (PET) bottles is recommended. Photo-degradation of riboflavin catalyzes photochemical oxidation and loss of ascorbic acid. Gamma radiation of 10 Gy destroys about 75% of riboflavin in liquid milk, whereas milk powder shows no losses even at higher doses. Storage influences riboflavin concentration as follows: condensed milk loses 28% (33%) of its initial riboflavin content when stored at 8–12 C for 2 years (10–15 C for 4 years), ice cream loses 5% when stored at –23 C for 7 months. No losses were found in fresh milk stored at 4–8 C for 24 h or in milk powder stored for 16 months. In cheese, most losses (66–88%) of the original riboflavin content of the milk appear to occur during whey
Vitamins | Riboflavin Table 2 Riboflavin in milk, dairy products, and cheese
5′ CH2OH
5′ CH2OH HO
HO Ribitol
OH
OH HO
HO
CH2
CH2 H3C
N
H3 C
N
N
O
H3C
N
H3C
N H
NH
H N
O NH
O
O 7,8-Dimethylisoaloxazine
Figure 1 Structures of oxidized (flavoquinone, left) and reduced (flavohydroquinone, right) forms of riboflavin (vitamin B2).
Adenosine(-5′)-diphosphate NH2 O 5′
CH2 O R
P
–
O
5′ CH2 O
O–
R
N
O
O
P O
P O CH2
O–
O–
O
HO
N
705
N N
OH
Figure 2 Structure of flavin mononucleotide (FMN, left) and flavin adenine dinucleotide (FAD, right). R: riboflavin.
Food
Concentration (g per 100 g)
Dried whole milk Parmigiano Camembert (45% fat in dry matter) Blue cheese (50% fat in dry matter) Condensed milk (min. 10% fat) Limburger (40% fat in dry matter) Quark/fresh cheese (from skim milk) Cream cheese (min. 60% fat in dry matter) Consumer milk (3.5% fat) UHT milk Yogurt (min. 3.5% fat) Skim milk Buttermilk Cream (min. 30% fat) Sweet whey Sterilized milk
1400 620 600 500 480 350 300 230 180 180 180 170 160 150 150 140
Milk from Sheep Cow Goat Buffalo Donkey Human
230 180 150 100 64 38
Reproduced with permission from Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers.
Table 1 Riboflavin concentration in food Food
Concentration (g per 100 g)
Brewers’ yeast Pig’s liver Ox liver Wheat germ Almonds Wheat bran Soybean, seed, dry Mushroom Egg Mackerel Eel Lentil, seed, dry Beef Pork Herring Maize
3800 3200 2900 720 620 510 460 436 408 360 320 262 260 230 220 200
Reproduced with prermission from Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers.
drainage, while ripening has almost no effects. However, in some cheese varieties, the concentration is higher in the outer layers due to microbial synthesis. High-pressure tests for thermal sterilization processes led to different results concerning the decay of the vitamin, depending on the matrix of the food tested.
Riboflavin Deficiency Riboflavin is essential for humans, animals, and some microorganisms. Among humans, seniors and adolescents seem to be at particular risk of deficiency; the recommended uptake is given in Table 3. In some cases, recommended Table 3 Recommended daily uptake of riboflavin Riboflavin (mg day–1) Age
Male
Sucklings <4 months Sucklings 4–12 months Children 1–4 years Children 4–7 years Children 7–10 years Children 10–13 years Children 13–15 years Adults 15–25 years Adults 25–51 years Adults 51–65 years Adults >65 years Pregnant Breast feeding
0.3 0.4 0.7 0.9 1.1 1.4 1.6 1.5 1.4 1.3 1.2
Female
1.2 1.3 1.2 1.2 1.2 1.2 1.5 1.6
Reproduced with permission from Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http:// www.dge.de/modules.php?name¼St&file¼w_referenzwerte (accessed April 2009).
706 Vitamins | Riboflavin
uptake is related to energy intake, and 0.6 mg riboflavin per 1000 kcal is considered adequate. Milk and milk products (without butter) can contribute about 30% of the total riboflavin supply. A major portion of riboflavin is bound to proteins and these flavoproteins have to be hydrolyzed before absorption by specialized transporters in the upper gastrointestinal tract. The amount that can be stored depends on the availability of proteins providing binding sites. Although a limited uptake makes sense in preventing accumulation in tissues, it increases the body’s dependence on dietary supply. Under normal conditions, riboflavin stores last for 2–6 weeks, but in cases of protein deficiency, they last significantly shorter. Symptoms of a marginal deficiency are often nonspecific: weakness, fatigue, mouth pain, glossitis, stomatitis, burning and itching of the eyes, and personality changes. Signs of increased deficiency are cheilosis; angular stomatitis; seborrheic dermatitis at the mouth, nasolabial sulcus, and ears (later extending to the trunk and extremities); desquamative dermatitis with itching in genital regions; opacity of the cornea; cataract; and brain dysfunction. The major reasons for riboflavin deficiency are dietary intake by seniors and adolescents • Insufficient (especially girls) abnormalities, insufficient adrenal and thyr• Endocrine oid hormones (psychotropic, anti-depressant, cancer therapeu• Drugs tics, anti-malarial) intake interfering with the digestion and • Alcohol absorption of food flavins that chelate or form complexes with riboflavin • Agents or FMN, affecting their bioavailability: copper, zinc, iron, caffeine, theophylline, saccharine, nicotinamide, ascorbic acid, tryptophan, urea. As riboflavin (via FAD-dependent glutathione reductase) is involved in antioxidant mechanisms, riboflavin deficiency may considerably affect erythrocyte metabolism. However, several studies have reported protective effects of a deficiency against malaria infection. A study in the United States showed that the uptake of yogurt, milk, cereals, and also riboflavin was inversely correlated with homocysteine levels in plasma, which, in turn, seem to be positively correlated with a higher risk of developing atherosclerosis. Assessment of the riboflavin (mainly by HPLC methods) status uses the following parameters: glutathione reductase activity coefficient, • Erythrocyte Excretion in urine (mg g creatinine to assess • short-term effects), and Riboflavin in erythrocytes (mg g hemoglobin). • –1
–1
Concerning supplementation, no case of intoxication has been described. Thus, riboflavin is regarded as safe even at high doses. Supplements are usually given to reverse deficiency symptoms or to support high-risk groups: intake of drugs (e.g., anti-depressants, oral • Regular contraceptive) • Malnutrition after trauma • Patients Malabsorption • Chronic alcoholics • Hyperbilirubinemia can be treated much quicker by phototherapy when 0.5 mg riboflavin per kg of bodyweight is given. Finally, persons with congenital methemoglobinemia might benefit from 20–40 mg day–1. See also: Milk Proteins: Minor Proteins, Bovine Serum Albumin, Vitamin-Binding Proteins. Vitamins: General Introduction.
Further Reading Ahmad I, Fasihullah Q, and Vaid FH (2006) Effect of light intensity and wavelengths on photodegradation reactions of riboflavin in aqueous solution. Journal of Photochemistry and Photobiology. B, Biology 82: 21–27. Biesalski HK (2004) Vitamine. In: Biesalski HK, Fu¨rst P, Kasper H et al. (eds.) Erna¨hrungsmedizin, 3rd edn., pp. 111–158. Stuttgart: Thieme. Bitsch R (2002) Vitamin B2 (riboflavin). In: Bieslaksi HK, Ko¨hrle J, and Schu¨mann K (eds.) Vitamine, Spurenelemente und Mineralstoffe, pp. 95–103. Stuttgart: Thieme. Bolander FF (2006) Vitamins: Not just for enzymes. Current Opinion in Investigational Drugs 7: 912–915. Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/modules.php?name¼St&file¼ w_referenzwerte (accessed April 2009). Fabian E, Majchrzak D, Dieminger B, Meyer E, and Elmadfa I (2008) Influence of probiotic and conventional yoghurt on the status of vitamins B1, B2 and B6 in young healthy women. Annals of Nutrition & Metabolism 52: 29–36. Ganji V and Kafai MR (2004) Frequent consumption of milk, yogurt, cold breakfast cereals, peppers, and cruciferous vegetables and intakes of dietary folate and riboflavin but not vitamins B-12 and B-6 are inversely associated with serum total homocysteine concentrations in the US population. The American Journal of Clinical Nutrition 80: 1500–1507. LeBlanc JG, Burgess C, Sesma F, Savoy de Giori G, Vansinderen D, and Powers HJ (2003) Riboflavin (vitamin B2) and health. The American Journal of Clinical Nutrition 77: 1352–1360. LeBlanc JG, Rutten G, Bruinenberg P, Sesma F, de Giori GS, and Smid EJ (2006) A novel dairy product fermented with Propionibacterium freudenreichii improves the riboflavin status of deficient rats. Nutrition 22: 645–651. LeBlanc JG, Sesma F, de Giori G, and vanSinderen D (2005) Ingestion of milk fermented by genetically modified Lactococcus lactis improves the riboflavin status of deficient rats. Journal of Dairy Science 88: 3435–3442. Said HM and Mohammed ZM (2006) Intestinal absorption of watersoluble vitamins: An update. Current Opinion in Gastroenterology 22: 140–146. Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers. Woolf K and Manore MM (2006) B-vitamins and exercise: Does exercise alter requirements? International Journal of Sport Nutrition and Exercise Metabolism 16: 453–484.
Riboflavin or Vitamin B2 The chemical name for riboflavin is 7,8-dimethyl-10-(19D-ribityl)isoalloxazine; riboflavin exists in an oxidized and a reduced form (Figure 1), from which two coenzymes are formed: flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD; Figure 2). The ending ‘flavin’ refers to its yellowish color (in Latin flavus means yellow). Free as well as protein-bound riboflavin occurs in the diet, and milk in general is the best source. In cow’s milk, the free form, with a higher bioavailability, is the major one (61% riboflavin, 26% FAD, 11% hydroxyethyl form, and others), whereas the protein-bound, and thus less bioavailable, form predominates in other foods. In human breast milk, approximately one- to two-thirds of riboflavin occurs as FAD. Riboflavin is very heat stable but it is extremely photosensitive. It is photodegraded to lumiflavin (under alkaline conditions) or lumichrome (under acidic conditions), both of which are biologically inactive. Concentrations are significantly reduced in high-pressure low-temperature treated milk as compared to raw milk. UV light excites riboflavin to a high degree of natural fluorescence, which is used for its detection and determination in yogurt or non-fat dry milk.
Functions of Riboflavin Riboflavin-dependent enzymes are called flavoproteins or flavoenzymes, because of their yellowish appearance. They catalyze hydroxylations, oxidative decarboxylations, dioxygenations, and reduction of oxygen to hydrogen peroxide, serving as electron carriers, mediators of electron transfer from pyridine nucleotides to cytochrome c or to other one-electron acceptors, and as catalysts of electron transfer from a metabolite to molecular oxygen. The two flavoenzymes, FMN and FAD, play major roles in the metabolism of glucose, fatty acids, amino acids, purines, drugs and steroids, folic acid, pyridoxine, vitamin K, niacin, and vitamin D.
704
The FAD-dependent enzyme, glutathione reductase, plays a major role in the antioxidant system by restoring reduced glutathione (GSH) from oxidized glutathione (GSSH). GSH is important in protecting lipids from peroxidation and in stabilizing the structure and function of red blood cells; it is the most important antioxidant in erythrocytes and in keeping lens proteins in solution (thus preventing cataracts). The formation of FMN and FAD is ATP dependent and takes place mainly in the liver, kidney, and heart. All enzymatic steps are under the control of thyroid hormones. riboflavin þ ATP ! r/FMN þ ADP • Flavokinase: FAD pyrophosphorylase: þ ATP ! /FAD þ PP • FAD þ apoenzyme/proteinFMN ! covalently bound flavins •
Sources of Riboflavin Tables 1 and 2 summarize dietary sources of riboflavin and its concentration, especially in the milk of various species and in dairy products. Heat treatment has only negligible effects on riboflavin concentrations, whereas exposure of milk to sunlight results in the loss of 20–80% of riboflavin. Thus, storage in dark bottles, light-tight wax cartons, or special polyethylene terephthalate (PET) bottles is recommended. Photo-degradation of riboflavin catalyzes photochemical oxidation and loss of ascorbic acid. Gamma radiation of 10 Gy destroys about 75% of riboflavin in liquid milk, whereas milk powder shows no losses even at higher doses. Storage influences riboflavin concentration as follows: condensed milk loses 28% (33%) of its initial riboflavin content when stored at 8–12 C for 2 years (10–15 C for 4 years), ice cream loses 5% when stored at –23 C for 7 months. No losses were found in fresh milk stored at 4–8 C for 24 h or in milk powder stored for 16 months. In cheese, most losses (66–88%) of the original riboflavin content of the milk appear to occur during whey
Vitamins | Riboflavin Table 2 Riboflavin in milk, dairy products, and cheese
5′ CH2OH
5′ CH2OH HO
HO Ribitol
OH
OH HO
HO
CH2
CH2 H3C
N
H3 C
N
N
O
H3C
N
H3C
N H
NH
H N
O NH
O
O 7,8-Dimethylisoaloxazine
Figure 1 Structures of oxidized (flavoquinone, left) and reduced (flavohydroquinone, right) forms of riboflavin (vitamin B2).
Adenosine(-5′)-diphosphate NH2 O 5′
CH2 O R
P
–
O
5′ CH2 O
O–
R
N
O
O
P O
P O CH2
O–
O–
O
HO
N
705
N N
OH
Figure 2 Structure of flavin mononucleotide (FMN, left) and flavin adenine dinucleotide (FAD, right). R: riboflavin.
Food
Concentration (g per 100 g)
Dried whole milk Parmigiano Camembert (45% fat in dry matter) Blue cheese (50% fat in dry matter) Condensed milk (min. 10% fat) Limburger (40% fat in dry matter) Quark/fresh cheese (from skim milk) Cream cheese (min. 60% fat in dry matter) Consumer milk (3.5% fat) UHT milk Yogurt (min. 3.5% fat) Skim milk Buttermilk Cream (min. 30% fat) Sweet whey Sterilized milk
1400 620 600 500 480 350 300 230 180 180 180 170 160 150 150 140
Milk from Sheep Cow Goat Buffalo Donkey Human
230 180 150 100 64 38
Reproduced with permission from Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers.
Table 1 Riboflavin concentration in food Food
Concentration (g per 100 g)
Brewers’ yeast Pig’s liver Ox liver Wheat germ Almonds Wheat bran Soybean, seed, dry Mushroom Egg Mackerel Eel Lentil, seed, dry Beef Pork Herring Maize
3800 3200 2900 720 620 510 460 436 408 360 320 262 260 230 220 200
Reproduced with prermission from Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers.
drainage, while ripening has almost no effects. However, in some cheese varieties, the concentration is higher in the outer layers due to microbial synthesis. High-pressure tests for thermal sterilization processes led to different results concerning the decay of the vitamin, depending on the matrix of the food tested.
Riboflavin Deficiency Riboflavin is essential for humans, animals, and some microorganisms. Among humans, seniors and adolescents seem to be at particular risk of deficiency; the recommended uptake is given in Table 3. In some cases, recommended Table 3 Recommended daily uptake of riboflavin Riboflavin (mg day–1) Age
Male
Sucklings <4 months Sucklings 4–12 months Children 1–4 years Children 4–7 years Children 7–10 years Children 10–13 years Children 13–15 years Adults 15–25 years Adults 25–51 years Adults 51–65 years Adults >65 years Pregnant Breast feeding
0.3 0.4 0.7 0.9 1.1 1.4 1.6 1.5 1.4 1.3 1.2
Female
1.2 1.3 1.2 1.2 1.2 1.2 1.5 1.6
Reproduced with permission from Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http:// www.dge.de/modules.php?name¼St&file¼w_referenzwerte (accessed April 2009).
706 Vitamins | Riboflavin
uptake is related to energy intake, and 0.6 mg riboflavin per 1000 kcal is considered adequate. Milk and milk products (without butter) can contribute about 30% of the total riboflavin supply. A major portion of riboflavin is bound to proteins and these flavoproteins have to be hydrolyzed before absorption by specialized transporters in the upper gastrointestinal tract. The amount that can be stored depends on the availability of proteins providing binding sites. Although a limited uptake makes sense in preventing accumulation in tissues, it increases the body’s dependence on dietary supply. Under normal conditions, riboflavin stores last for 2–6 weeks, but in cases of protein deficiency, they last significantly shorter. Symptoms of a marginal deficiency are often nonspecific: weakness, fatigue, mouth pain, glossitis, stomatitis, burning and itching of the eyes, and personality changes. Signs of increased deficiency are cheilosis; angular stomatitis; seborrheic dermatitis at the mouth, nasolabial sulcus, and ears (later extending to the trunk and extremities); desquamative dermatitis with itching in genital regions; opacity of the cornea; cataract; and brain dysfunction. The major reasons for riboflavin deficiency are dietary intake by seniors and adolescents • Insufficient (especially girls) abnormalities, insufficient adrenal and thyr• Endocrine oid hormones (psychotropic, anti-depressant, cancer therapeu• Drugs tics, anti-malarial) intake interfering with the digestion and • Alcohol absorption of food flavins that chelate or form complexes with riboflavin • Agents or FMN, affecting their bioavailability: copper, zinc, iron, caffeine, theophylline, saccharine, nicotinamide, ascorbic acid, tryptophan, urea. As riboflavin (via FAD-dependent glutathione reductase) is involved in antioxidant mechanisms, riboflavin deficiency may considerably affect erythrocyte metabolism. However, several studies have reported protective effects of a deficiency against malaria infection. A study in the United States showed that the uptake of yogurt, milk, cereals, and also riboflavin was inversely correlated with homocysteine levels in plasma, which, in turn, seem to be positively correlated with a higher risk of developing atherosclerosis. Assessment of the riboflavin (mainly by HPLC methods) status uses the following parameters: glutathione reductase activity coefficient, • Erythrocyte Excretion in urine (mg g creatinine to assess • short-term effects), and Riboflavin in erythrocytes (mg g hemoglobin). • –1
–1
Concerning supplementation, no case of intoxication has been described. Thus, riboflavin is regarded as safe even at high doses. Supplements are usually given to reverse deficiency symptoms or to support high-risk groups: intake of drugs (e.g., anti-depressants, oral • Regular contraceptive) • Malnutrition after trauma • Patients Malabsorption • Chronic alcoholics • Hyperbilirubinemia can be treated much quicker by phototherapy when 0.5 mg riboflavin per kg of bodyweight is given. Finally, persons with congenital methemoglobinemia might benefit from 20–40 mg day–1. See also: Milk Proteins: Minor Proteins, Bovine Serum Albumin, Vitamin-Binding Proteins. Vitamins: General Introduction.
Further Reading Ahmad I, Fasihullah Q, and Vaid FH (2006) Effect of light intensity and wavelengths on photodegradation reactions of riboflavin in aqueous solution. Journal of Photochemistry and Photobiology. B, Biology 82: 21–27. Biesalski HK (2004) Vitamine. In: Biesalski HK, Fu¨rst P, Kasper H et al. (eds.) Erna¨hrungsmedizin, 3rd edn., pp. 111–158. Stuttgart: Thieme. Bitsch R (2002) Vitamin B2 (riboflavin). In: Bieslaksi HK, Ko¨hrle J, and Schu¨mann K (eds.) Vitamine, Spurenelemente und Mineralstoffe, pp. 95–103. Stuttgart: Thieme. Bolander FF (2006) Vitamins: Not just for enzymes. Current Opinion in Investigational Drugs 7: 912–915. Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/modules.php?name¼St&file¼ w_referenzwerte (accessed April 2009). Fabian E, Majchrzak D, Dieminger B, Meyer E, and Elmadfa I (2008) Influence of probiotic and conventional yoghurt on the status of vitamins B1, B2 and B6 in young healthy women. Annals of Nutrition & Metabolism 52: 29–36. Ganji V and Kafai MR (2004) Frequent consumption of milk, yogurt, cold breakfast cereals, peppers, and cruciferous vegetables and intakes of dietary folate and riboflavin but not vitamins B-12 and B-6 are inversely associated with serum total homocysteine concentrations in the US population. The American Journal of Clinical Nutrition 80: 1500–1507. LeBlanc JG, Burgess C, Sesma F, Savoy de Giori G, Vansinderen D, and Powers HJ (2003) Riboflavin (vitamin B2) and health. The American Journal of Clinical Nutrition 77: 1352–1360. LeBlanc JG, Rutten G, Bruinenberg P, Sesma F, de Giori GS, and Smid EJ (2006) A novel dairy product fermented with Propionibacterium freudenreichii improves the riboflavin status of deficient rats. Nutrition 22: 645–651. LeBlanc JG, Sesma F, de Giori G, and vanSinderen D (2005) Ingestion of milk fermented by genetically modified Lactococcus lactis improves the riboflavin status of deficient rats. Journal of Dairy Science 88: 3435–3442. Said HM and Mohammed ZM (2006) Intestinal absorption of watersoluble vitamins: An update. Current Opinion in Gastroenterology 22: 140–146. Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers. Woolf K and Manore MM (2006) B-vitamins and exercise: Does exercise alter requirements? International Journal of Sport Nutrition and Exercise Metabolism 16: 453–484.