Thiamin, Riboflavin, Niacin, Vitamin B6, Pantothenic Acid and Biotin...continued #2.

Reference from the joint report of FAO/WHO expert consultation on Human Vitamins and Minerals verbatim. (Chapter 3)

Riboflavin

Background with requisite function in human metabolic processes.

Deficiency

8. McCormick, D.B. 1997. Vitamin, Structure and Function of. In: Encyclopedia of Molecular Biology and Molecular Medicine, Vol. 6. Meyers, R.A., ed. Weinheim: VCH, p. 244-52.

29. McCormick, D.B. 1994. Riboflavin. In: Modern Nutrition in Health and Disease, 8th edition. Shils, M.E., Olson, J.A., Shike, M., eds. Philadelphia: Lea & Febiger, p. 366-75.

Riboflavin (vitamin B2) deficiency results in the condition of hypo- or ariboflavinosis, with sore throat; hyperaemia; oedema of the pharyngeal and oral mucous membranes; cheilosis; angular stomatitis; glossitis; seborrheic dermatitis; and normochromic, normocytic bone marrow (8, 29).

Because the deficiency almost invariably occurs combined with a deficiency of other B-complex vitamins, some of the symptoms (e.g., glossitis and dermatitis) may result from other complicating deficiencies. The major cause of hypo-riboflavinosis is inadequate dietary intake as a result of limited food supply, which is sometimes exacerbated by poor foodstorage or processing.

Children in developing countries will commonly demonstrate clinical signs of riboflavin deficiency during periods of the year when gastrointestinal infections are prevalent. Decreased assimilation of riboflavin also results from abnormal digestion such as that which occurs with lactose intolerance. This condition is highest in African and Asian populations and can lead to a decreased intake of milk as well as an abnormal absorption of the vitamin.

Absorption of riboflavin is also affected in some other conditions, for example, tropical sprue, celiac disease, malignancy and resection of the small bowel, and decreased gastrointestinal passage time. In relatively rare cases the causes of deficiency are inborn errors in which the genetic defect is in the formation of a flavoprotein (e.g., acyl-co-enzyme A [co-A] dehydrogenases). 

Also at risk are those receiving phototherapy for neonatal jaundice and perhaps those with inadequate thyroid hormone. Some cases of riboflavin deficiency were also observed in Russian schoolchildren (Moscow) and Southeast Asian schoolchildren (infected with hookworm).

Toxicity

Riboflavin toxicity is not a problem because of limited intestinal absorption.

Functions

10. McCormick, D.B. 1996. Co-enzymes, Biochemistry of. In: Encyclopedia of Molecular Biology and Molecular Medicine, Vol. 1. Meyers, R.A., ed. Weinheim: VCH, p. 396-406.

11. McCormick, D.B. 1997. Co-enzymes, Biochemistry. In: Encyclopedia of Human Biology 2nd edition. Dulbecco, R., ed.-in-chief. San Diego: Academic Press, p. 847-64.

Conversion of riboflavin to flavin mononucleotide (FMN) and further to the predominant flavin adenine dinucleotide (FAD) occurs before these flavins form complexes with numerous flavoprotein dehydrogenases and oxidases. These flavoco-enzymes (FMN and FASD) participate in oxidation-reduction reactions in metabolic pathways and in energy production via the respiratory chain (10, 11).

Biochemical indicators

Indicators used to estimate riboflavin requirements are urinary flavin excretion, erythrocyte glutathione reductase activity coefficient, and erythrocyte flavin. The urinary flavin excretion rate of vitamin and metabolites reflects intake; validity of assessment of riboflavin adequacy is improved with load test. Erythrocyte glutathione reductase activity coefficient reflects FAD levels; results are confounded by such genetic defects as glucose-6-phosphate dehydrogenase deficiency and heterozygous β thalassemia. Erythrocyte flavin is mainly a measure of FMN and riboflavin after hydrolysis of labile FAD and HPLC separation.

6. Food and Nutrition Board, Institute of Medicine/National Academy of Sciences- National Research Council. 1998. Dietary Reference Intake: Folate, Other B Vitamins, and Choline. Washington, D.C., National Academy Press.

9. McCormick, D.B & Greene, H.L. 1994. Vitamins. In: Tietz Textbook of Clin Chem., 2nd edition. Burtis, V.A., Ashwood, E.R., eds. Philadelphia: W.B. Saunders, p. 1275-1316.

29. McCormick, D.B. 1994. Riboflavin. In: Modern Nutrition in Health and Disease, 8th edition. Shils, M.E., Olson, J.A., Shike, M., eds. Philadelphia: Lea & Febiger, p. 366-75.

30. Smith, M.D. 1980. Rapid method for determination of riboflavin in urine by highperformance liquid chromatography. J. Chromatogr., 182: 285-91.

Riboflavin status has been assessed by measuring urinary excretion of the vitamin in fasting, random, and 24-hour specimens or by load returns tests (amounts measured after a specific amount of riboflavin is given orally); erythrocyte glutathione reductase; or erythrocyte flavin concentration (6, 9, 29). The HPLC method with fluorometry gives lower values for urinary riboflavin than do fluorometric methods, which measure the additive fluorescence ofsimilar flavin metabolites (30).

31. Chastain, J.L. & McCormick, D.B. 1987. Flavin catabolites: identification and quantitation in Human urine. Am. J. Clin. Nutr., 46: 830-4.

32. Roughead, Z.K. & McCormick, D.B. 1991. Urinary riboflavin and its metabolites: effects of riboflavin supplementation in healthy residents of rural Georgia (USA). Eur. J. Clin. Nutr., 45: 299-307. 

33. Aw, T.-Y., Jones, D.P. & McCormick, D.B. 1983. Uptake of riboflavin by isolated rat liver cells. J. Nutr., 113: 1249-54.

The metabolites can comprise as much as one-third of total urinary flavin (31, 32) and in some cases may depress assays dependent on a biologic response because certain catabolites can inhibit cellular uptake (33). Under conditions of adequate riboflavin uptake (≈1.5 mg/day) by adults, an estimated 120 μg (320 nmol) total riboflavin or 80 μg/g of creatinine is excreted daily (32).

34. Nichoalds, G.E. 1981. Riboflavin. Symposium in Laboratory Medicine. In: Labbac RF, ed. Symposium on Laboratory Assessment of Nutritional Status. Clinics in Laboratory Medicine. Philadelphia: W.B. Saunders, 1: 685-98.

35. Sadowski, J.A. 1992. Riboflavin. In: Nutrition in the Elderly. The Boston Nutritional
Status Survey. Hartz, S.C., Russell, R.M., Rosenberg, I.H. eds. London: Smith-Gordon, p.
119-25.

The erythrocyte glutathione reductase assay, with an activity coefficient (AC) expressing the ratio of activities in the presence and absence of added FAD, continues to be used as a main functional indicator, but some limits have been noted. The reductase in erythrocytes from individuals with glucose-6-phosphate dehydrogenase deficiency (often present in blacks) has an increased avidity for FAD, which makes this test invalid (34). Sadowski (35) has set an upper limit of normality for the AC at 1.34 based on the mean value plus 2 standard deviations from several hundreds of apparently healthy individuals aged 60 years and over.

 9. McCormick, D.B & Greene, H.L. 1994. Vitamins. In: Tietz Textbook of Clin Chem., 2nd edition. Burtis, V.A., Ashwood, E.R., eds. Philadelphia: W.B. Saunders, p. 1275-1316.

36. Ramsay, V.P., Neumann, C., Clark, V. & Swenseid, M.E. 1983. Vitamin cofactor saturation indices for riboflavin, thiamine, and pyridoxine in placental tissue of Kenyan women. Am. J. Clin. Nutr., 37: 969-73.

Suggested guidelines for the interpretation of such enzyme ACs are as follows: less than 1.2, acceptable; 1.2–1.4, low; greater than 1.4, deficient (9). In general agreement with earlier findings on erythrocyte flavin, Ramsay et al. (36) found a correlation between cord blood and maternal erythrocyte deficiencies and suggested that values greater than 40 nmol/l are considered adequate.

Factors affecting requirements

37. Belko, A.Z., Obarzanek, E., Kalkwarf, H.J., Rotter, M.A., Bogusz, S., Miller, D., Haas, J.D. & Roe, D.A. 1983. Effects of exercise on riboflavin requirements of young women. Am. J. Clin. Nutr., 37: 509-17.

38. Belko, A.Z., Obarzanek, E., Roach, R., Rotten, M., Urban, G., Weinberg, S. & Roe, D.A. 1984. Effects of aerobic exercise and weight loss on riboflavin requirements of moderately obese, marginally deficient young women. Am. J. Clin. Nutr., 40: 553-61.

39. Belko, A.Z., Meredith, M.P., Kalkwarf, H.J., Obarzanek, E., Weinberg, S., Roach, R., McKeon, G. & Roe, D.A. 1985. Effects of exercise on riboflavin requirements: biological validation in weight reducing women. Am. J. Clin. Nutr., 41: 270-7.

40. Soares, M.J., Satyanarayana, K., Bamji, M.S., Jacob, C.M., Ramana, Y.V. & Rao, S.S. 1993. The effect of exercise on the riboflavin status of adult men. Br. J. Nutr., 69: 541-51.

41. Winters, L.R., Yoon, J.S., Kalkwarf, H.J., Davies, J.C., Berkowitz, M.G., Haas, J. & Roe, D.A. 1992. Riboflavin requirements and exercise adaptation in older women. Am. J. Clin. Nutr., 56: 526-32.

Several studies reported modest effects of physical activity on the erythrocyte glutathione reductase AC (37-41). A slight increase in the AC and decrease in urinary flavin of weight reducing women (39) and older women undergoing exercise training (41) were “normalised” with 20 percent additional riboflavin. However, riboflavin supplementation did not lead to an increase in work performance when such subjects were not clinically deficient (42-45).

6. Food and Nutrition Board, Institute of Medicine/National Academy of Sciences- National Research Council. 1998. Dietary Reference Intake: Folate, Other B Vitamins, and Choline. Washington, D.C., National Academy Press.

46. Zempleni, J., Galloway, J.R. & McCormick, D.B. 1996. Pharmacokinetics of orally and intravenously administered riboflavin in healthy Humans. Am. J. Clin. Nutr., 63: 54-66.

47. Chia, C.P., Addison, R. & McCormick, D.B. 1978. Absorption, metabolism, and excretion of 8a-(amino acid)-riboflavins in the rat. J. Nutr., 108: 373-81.

48. Boisvert, W.A., Mendoza, I., Castañeda, C., DePortocarrero, L., Solomons, N.W., Gershoff, S.N. & Russell, R.M. 193. Riboflavin requirement of healthy elderly Humans and its relationship to macronutrient composition of the diet. J. Nutr., 123: 915-25.

Bio-availability of riboflavin in foods, mostly as digestible flavoco-enzymes, is excellent at nearly 95 percent (6), but absorption of the free vitamin is limited to about 27 mg per single meal or dose in an adult (46). No more than about 7 percent of food flavin is found as 8α-FAD covalently attached to certain flavoprotein enzymes. Although some portions of the 8α-(amino acid)-riboflavins are released by proteolysis of these flavoproteins, they do not have vitamin activity (47). A lower fat-to-carbohydrate ratio may decrease the riboflavin requirements of the elderly (48).

49. McCormick, D.B. 1989. Two interconnected B vitamins: riboflavin and pyridoxine. Physiol. Revs., 69: 1170-98.

50. Roe, D.A., Bogusz, S., Sheu, J. & McCormick, D.B. 1982. Factors affecting riboflavin requirements of oral contraceptive users and nonusers. Am. J. Clin. Nutr., 35: 495-501.

Riboflavin interrelates with other B vitamins, notably niacin, which requires FAD for its formation from tryptophan, and vitamin B6, which requires FMN for conversion of the phosphates of pyridoxine and pyridoxamine to the co-enzyme pyridoxal 5'-phosphate (PLP) (49). Contrary to earlier reports, no difference was seen in riboflavin status of women taking oral contraceptives when dietary intake was controlled by providing a single basic daily menu and meal pattern after 0.6 mg riboflavin/418 kJ was given in a 2-week acclimation period (50).

Findings by age and life stage

51. Thomas, M.R., Sneed, S.M., Wei, C., Nail, P.A., Wilson, M. & Sprinkle, E.E., III. 1980. The effects of vitamin C, vitamin B6, vitamin B12, folic acid, riboflavin, and thiamin on the breast milk and maternal status of well-nourished women at 6 months postpartum. Am. J. Clin. Nutr., 33: 2151-6.

52. Roughead, Z.K. & McCormick, D.B. 1990. Flavin composition of Human milk. Am. J. Clin. Nutr., 52: 854-7.

53. Roughead, Z.K. & McCormick, D.B. 1990. A qualitative and quantitative assessment of flavins in cow's milk. J. Nutr., 120: 382-8.

As reviewed by Thomas et al. (51), early estimates of riboflavin content in human milk showed changes during the post-partum period. More recent investigations of flavin composition of both human (52) and cow (53) milk have helped clarify the nature of the flavins present and provide better estimates of riboflavin equivalence. For human milk consumed by infants up to age 6 months, the riboflavin equivalence averages 0.35mg (931 nmol) /l (6) or 0.26 mg (691nmol) /0.75 l of milk per day.

54. Bamji, M.S., Chowdhury, N., Ramalakshmi, B.A. & Jacob, C.M. 1991. Enzymatic evaluation of riboflavin status of infants. Eur. J. Clin. Nutr., 45: 309-13. 

For low-income Indian women with erythrocyte glutathione reductase activity ratios averaging 1.80 and a milk riboflavin content of 0.22 mg/l, breast-fed infants averaged AC ratios near 1.36 (54). Hence, a deficiency sufficient to reduce human-milk riboflavin content by one-third can lead to a mild sub-clinical deficiency in infants.

38. Belko, A.Z., Obarzanek, E., Roach, R., Rotten, M., Urban, G., Weinberg, S. & Roe, D.A. 1984. Effects of aerobic exercise and weight loss on riboflavin requirements of moderately obese, marginally deficient young women. Am. J. Clin. Nutr., 40: 553-61.

39. Belko, A.Z., Meredith, M.P., Kalkwarf, H.J., Obarzanek, E., Weinberg, S., Roach, R., McKeon, G. & Roe, D.A. 1985. Effects of exercise on riboflavin requirements: biological validation in weight reducing women. Am. J. Clin. Nutr., 41: 270-7.

55. Bates, C.J., Powers, H.J., Downes, R., Brubacher, D., Sutcliffe, V. & Thurnhill, A. 1989. Riboflavin status of adolescent vs. elderly Gambian subjects before and during supplementation. Am. J. Clin. Nutr., 50: 825-9.

Studies of riboflavin status in adults include those by Belko et al. (38, 39) in modestly obese young women on low-energy diets, by Bates et al. (55) on deficient Gambians, and by adults consuming at least this amount was largely excreted in the urine (32). Such findings corroborate earlier work indicating a relative saturation of tissue with intakes above 1.1 mg/day.

57. Alexander, M., Emanuel, G., Golin, T., Pinto, J.T. & Rivlin, R.S. 1984. Relation of riboflavin nutriture in healthy elderly to intake of calcium and vitamin supplements: evidence against riboflavin supplementation. Am. J. Clin. Nutr., 39: 540-6. 

48. Boisvert, W.A., Mendoza, I., Castañeda, C., DePortocarrero, L., Solomons, N.W., Gershoff, S.N. & Russell, R.M. 193. Riboflavin requirement of healthy elderly Humans and its relationship to macronutrient composition of the diet. J. Nutr., 123: 915-25.

Studies by Alexander et al. (57) on riboflavin status in the elderly show that doubling the estimated riboflavin intakes of 1.7 mg/day for women aged 70 years and over, with a reductase AC of 1.8, led to a doubling of urinary riboflavin from 1.6–3.4 μg (4.2 to 9.0 nmol) /mg creatinine and a decrease in AC to 1.25. Boisvert et al. (48) obtained normalisation of theglutathione reductase AC in elderly Guatemalans with approximately 1.3 mg/day of riboflavin, with a sharp increase in urinary riboflavin occurring at intakes above 1.0–1.1 mg/day.

56. Kuizon, M.D., Natera, M.G., Alberto, S.P., Perlas, L.A., Desnacido, J.A., Avena, E.M., Tajaon, R.T. & Macapinlac, M.P. 1992. Riboflavin requirement of Filipino women. Eur. J. Clin. Nutr., 46: 257-64.

58. Bates, C.J., Prentice, A.M., Paul, A.A., Sutcliffe, B.A., Watkinson, M. & Whitehead, R.G. 1981. Riboflavin status in Gambian pregnant and lactating women and its implications for recommended Dietary Allowances. Am. J. Clin. Nutr., 34: 928-35.

59. Vir, S.C., Love, A.H. & Thompson, W. 1981. Riboflavin status during pregnancy. Am. J. Clin. Nutr., 34: 2699-705.

60. Badart-Smook, A., van Houwelingen, A.C., Al, M.D., Kester, A.D. & Hornstra, G. 1997. Foetal growth is associated positively with maternal intake of riboflavin and negatively with maternal intake of linoleic acid. J. Am. Diet. Assoc., 97: 867-70.

Pregnant women have an increased erythrocyte glutathione reductase AC (58, 59). Kuizon et al. (56) found that riboflavin at 0.7 mg /4184 kJ was needed to lower the AC of four of eight pregnant women to 1.3 within 20 days, whereas only 0.41 mg/4184 kJ was needed for five of the seven non-pregnant women. Maternal riboflavin intake was positively associated with foetal growth in a study of 372 pregnant women (60).

The additional riboflavin requirement of 0.3 mg/day for pregnancy is an estimate based on increased growth in maternal and foetal compartments. For lactating women, an estimated 0.3 mg riboflavin is transferred in milk daily and, because utilisation for milk production is assumed to be 70 percent efficient, the value is adjusted upward to 0.4 mg/day.

Recommendations

The recommendations for riboflavin are given in Table 7.