10.2: Vitamins Important for Metabolism and Blood Function

Learning Objectives

• Summarize the role of the B vitamins in metabolism.
• Describe the role of the B vitamins in blood function.
• Explain how Vitamin K supports blood function.

While the macronutrients (carbohydrates, lipids, and proteins) and alcohol can be broken down (catabolized) to release energy, vitamins and minerals play a different kind of role in energy metabolism; they are required as functional parts of enzymes involved in energy release and storage. In other words, they're necessary for obtaining energy from the macronutrients (vitamins and minerals don't directly provide energy/calories). Vitamins and minerals that make up part of enzymes are referred to as coenzymes and cofactors, respectively. Coenzymes and cofactors are required by enzymes to catalyze a specific reaction. They assist in converting a substrate to an end-product (Figure \(\PageIndex{1}\)). Coenzymes and cofactors play many roles in catabolic and anabolic pathways.

Figure \(\PageIndex{1}\): Coenzymes and cofactors are the particular vitamin or mineral required for enzymes to catalyze a specific reaction. (CC BY 4.0; by OpenStax)

In addition to being essential for metabolism, many vitamins and minerals are required for blood to function properly. At insufficient levels in the diet these vitamins and minerals impair the health of blood and consequently the delivery of nutrients and removal of wastes. In this section we will focus on the vitamins that take part in metabolism and blood function.

Thiamin (Vitamin B₁)

The water-soluble vitamin, thiamin, is especially important in glucose metabolism. It acts as a coenzyme for enzymes that break down glucose and branched chain amino acids for energy production. Additionally, thiamin plays a role in the synthesis of ribose from glucose and is therefore required for RNA, DNA, and ATP synthesis. The brain and heart are most affected by a deficiency in thiamin. Thiamin deficiency, also known as beriberi, can cause symptoms of fatigue, confusion, muscle wasting, nerve damage, movement impairment, pain in the lower extremities, swelling, and heart failure. The DRIs for thiamin are listed in Table \(\PageIndex{1}\). A Tolerable Upper Intake Level (UL) for thiamin has not been set. Food sources of thiamin include whole grains, meat, fish, and enriched or fortified grains. Other good food sources of thiamin are included in Table \(\PageIndex{2}\).

Table \(\PageIndex{1}\): Dietary Reference Intakes for Thiamin¹

Age Group	RDA (mg/day)
Infants (0–6 months)	0.2*
Infants (7–12 months)	0.3*
Children (1–3 years)	0.5
Children (4–8 years)	0.6
Children (9–13 years)	0.9
Adolescents (14–18 years)	1.2 (males), 1.0 (females)
Adults (> 19 years)	1.2 (males), 1.1 (females)
* denotes Adequate Intake

 

Table \(\PageIndex{2}\): Dietary Sources of Thiamin²

Food	Thiamin (mg)	% Daily Value
Rice, white, enriched, cooked (1/2 cup)	1.4	117
Breakfast cereals, fortified (1 serving)	1.2	100
Pork chop (3 ounces)	0.4	33
Black beans, boiled (1/2 cup)	0.4	33

Learn even more about this nutrient by reading the Thiamin Fact Sheet from the National Institutes of Health, Office of Dietary Supplements.

Riboflavin (Vitamin B₂)

Riboflavin is a water-soluble vitamin that is an essential component of flavoproteins, which are coenzymes involved in many metabolic pathways of carbohydrate, lipid, and protein metabolism. Furthermore, the functions of other B-vitamin coenzymes, such as vitamin B₆ and folate, are dependent on the actions of flavoproteins. In addition, riboflavin is part of the antioxidant enzyme glutathione peroxidase. The “flavin” portion of riboflavin gives a bright yellow color to riboflavin, an attribute that led to its discovery as a vitamin. Riboflavin is destroyed when exposed to light. Riboflavin deficiency (ariboflavinosis) is rare but when it occurs is often accompanied by other dietary deficiencies (most notably protein) and can be common in people that suffer from alcoholism. Signs and symptoms of riboflavin deficiency include dry, scaly skin, mouth inflammation and sores, sore throat, itchy eyes, fatigue, muscle weakness, and light sensitivity. The DRIs for riboflavin are listed in Table \(\PageIndex{3}\). A Tolerable Upper Intake Level (UL) for riboflavin has not been set. Food sources of riboflavin include eggs, meat, and milk. Other good food sources of riboflavin are included in Table \(\PageIndex{4}\).

Table \(\PageIndex{3}\): Dietary Reference Intakes for Riboflavin¹

Age Group	RDA (mg/day)
Infants (0–6 months)	0.3*
Infants (7–12 months)	0.4*
Children (1–3 years)	0.5
Children (4–8 years)	0.6
Children (9–13 years)	0.9
Adolescents (14–18 years)	1.3 (males), 1.0 (females)
Adults (> 19 years)	1.3 (males), 1.1 (females)
* denotes Adequate Intake

 

Table \(\PageIndex{4}\): Dietary Sources of Riboflavin³

Food	Riboflavin (mg)	% Daily Value
Beef liver (3 ounces)	2.9	223
Breakfast cereals, fortified (1 serving)	1.3	100
Yogurt, plain, fat free (1 cup)	0.6	46
Portabella mushrooms (1/2 cup)	0.3	23
Almonds (1 ounce)	0.3	23

Learn even more about this nutrient by reading the Riboflavin Fact Sheet from the National Institutes of Health, Office of Dietary Supplements.

Niacin (Vitamin B₃)

Niacin is a water-soluble vitamin that is a component of coenzymes involved in the catabolism and/or anabolism of carbohydrates, lipids, and proteins. Niacin deficiency is commonly known as pellagra and is characterized by diarrhea, dermatitis, dementia, and sometimes death. Niacin toxicity may result from taking niacin supplements; symptoms include flushing (burning, tingling, itching, and red skin). The DRIs for niacin are listed in Table \(\PageIndex{5}\). Niacin is present in a wide variety of foods including those listed in Table \(\PageIndex{6}\).

Table \(\PageIndex{5}\): Dietary Reference Intakes for Niacin¹

Age Group	RDA (mg/day)	UL (mg/day)
Infants (0–6 months)	2*	ND
Infants (7–12 months)	4*	ND
Children (1–3 years)	6	10
Children (4–8 years)	8	15
Children (9–13 years)	12	20
Adolescents (14–18 years)	16 (males), 14 (females)	30
Adults (> 19 years)	16 (males), 14 (females)	35
* denotes Adequate Intake; ND=not determined

 

Table \(\PageIndex{6}\): Dietary Sources of Niacin⁴

Food	Niacin (mg)	% Daily Value
Beef liver (3 ounces)	14.9	93
Chicken breast (3 ounces)	10.3	64
Salmon (3 ounces)	8.6	54
Peanuts (1 ounce)	4.2	26
Potato, baked (1 medium)	2.3	14

Learn even more about this nutrient by reading the Niacin Fact Sheet from the National Institutes of Health, Office of Dietary Supplements.

Vitamin B₆

Vitamin B₆ is a water-soluble vitamin and coenzyme involved in nitrogen transfer between amino acids (transamination) and therefore plays a role in non-essential amino acid synthesis and catabolism. Also, it functions to release glucose from glycogen in the catabolic pathway of glycogenolysis and is required by enzymes for the synthesis of multiple neurotransmitters and hemoglobin. A deficiency in vitamin B₆ can cause signs and symptoms of muscle weakness, dermatitis, mouth sores, fatigue, and confusion. Vitamin B₆ is a required coenzyme for the synthesis of hemoglobin. A deficiency in vitamin B₆ can cause a type of anemia where the red blood cell size is normal or somewhat smaller but the hemoglobin content is lower. This means each red blood cell has less capacity for carrying oxygen, resulting in muscle weakness, fatigue, and shortness of breath. A deficiency of vitamin B₆ is also associated with an increased risk of cardiovascular disease due to elevated homocysteine levels. Vitamin B₆ toxicity may result from supplements and lead to nerve damage. The DRIs for vitamin B₆ are listed in Table \(\PageIndex{7}\). Vitamin B₆ is present in a wide variety of foods including those listed in Table \(\PageIndex{8}\).

Table \(\PageIndex{7}\): Dietary Reference Intakes for Vitamin B₆¹

Age Group	RDA (mg/day)	UL (mg/day)
Infants (0–6 months)	0.1*	ND
Infants (7–12 months)	0.3*	ND
Children (1–3 years)	0.5	30
Children (4–8 years)	0.6	40
Children (9–13 years)	1.0	60
Adolescents (14–18 years)	1.3 (males), 1.2 (females)	80
Adults (19-50 years)	1.3	100
Adults (> 50 years)	1.7 (males), 1.5 (females)	100
* denotes Adequate Intake; ND=not determined

 

Table \(\PageIndex{8}\): Dietary Sources of Vitamin B₆⁵

Food	Vitamin B6 (mg)	% Daily Value
Chickpeas (1 cup)	1.1	65
Yellowfin tuna (3 ounces)	0.9	53
Chicken breast (3 ounces)	0.5	29
Potatoes, boiled (1 cup)	0.4	25
Banana (1 medium)	0.4	25

Learn even more about this nutrient by reading the Vitamin B₆ Fact Sheet from the National Institutes of Health, Office of Dietary Supplements.

Biotin

Biotin, a water-soluble vitamin, is required as a coenzyme in lipid metabolism. It is also required as an enzyme in the synthesis of glucose and some nonessential amino acids. Biotin is important for gluconeogenesis (the generation of new glucose from amino acids when carbohydrate intake is low). Biotin deficiency is rare, but can be caused by eating large amounts of raw egg whites over an extended period of time. This is because a protein in raw egg whites tightly binds to biotin making it unavailable for absorption. The Adequate Intakes (AIs) for biotin are listed in Table \(\PageIndex{9}\). A Tolerable Upper Intake Level (UL) for biotin has not been set. Food sources of biotin include eggs, meat, and fish (Table \(\PageIndex{10}\)).

Table \(\PageIndex{9}\): Dietary Reference Intakes for Biotin¹

Age Group	AI (mcg/day)
Infants (0–6 months)	5
Infants (7–12 months)	6
Children (1–3 years)	8
Children (4–8 years)	12
Children (9–13 years)	20
Adolescents (14–18 years)	25
Adults (> 19 years)	30

 

Table \(\PageIndex{10}\): Dietary Sources of Biotin⁶

Food	Biotin (mcg)	% Daily Value
Beef liver (3 ounces)	30.8	103
Egg, whole, cooked (1 large)	10.0	33
Salmon, canned (3 ounces)	5.0	17
Pork chop (3 ounces)	3.8	13
Sunflower seeds (1/4 cup)	2.6	9

Learn even more about this nutrient by reading the Biotin Fact Sheet from the National Institutes of Health, Office of Dietary Supplements.

Folate

Folate, a water-soluble vitamin, is a required coenzyme for the synthesis of the amino acid methionine as well as RNA and DNA synthesis. Therefore, rapidly dividing cells are most affected by folate deficiency. Folate is especially essential for the growth and specialization of cells of the central nervous system. Children whose mothers were folate-deficient during pregnancy have a higher risk of neural-tube birth defects such as spina bifida, a neural-tube defect that occurs when the spine does not completely enclose the spinal cord (Figure \(\PageIndex{2}\)). Observational studies show that the prevalence of neural-tube defects in the United States decreased after the fortification of enriched cereal grain products with folate began in 1996 compared to before grain products were fortified with folate.

Figure \(\PageIndex{2}\): Spina bifida is a neural-tube defect that can have severe health consequences. (CC0; by Centers for Disease Control and Prevention via Wikimedia Commons)

Folate deficiency can lead to macrocytic (also called megaloblastic) anemia. Macrocytic and megaloblastic mean “big cell,” and anemia refers to fewer red blood cells or red blood cells containing less hemoglobin. Macrocytic anemia is characterized by larger and fewer red blood cells. It is caused by red blood cells being unable to produce DNA and RNA fast enough—cells grow but do not divide, making them large in size. Folate toxicity can occur when taking supplements. Excess folate can mask a vitamin B₁₂ deficiency which can lead to nerve damage. The DRIs for folate are listed in Table \(\PageIndex{11}\). Folate is present in a wide variety of foods including those listed in Table \(\PageIndex{12}\). Folate is sensitive to heat and can lost when foods are cooked.

Table \(\PageIndex{11}\): Dietary Reference Intakes for Folate¹

Age Group	RDA (mcg/day)	UL (mcg/day)
Infants (0–6 months)	65*	ND
Infants (7–12 months)	80*	ND
Children (1–3 years)	150	300
Children (4–8 years)	200	400
Children (9–13 years)	300	600
Adolescents (14–18 years)	400	800
Adults (> 18 years)	400	1,000
* denotes Adequate Intake; ND=not determined

 

Table \(\PageIndex{12}\): Dietary Sources of Folate⁷

Food	Folate (mcg)	% Daily Value
Spinach, boiled (1/2 cup)	131	33
Black-eyed pea, boiled (1/2 cup)	105	26
Rice, white, cooked (1/2 cup)	90	22
Asparagus (4 spears)	89	22
Lettuce, romaine (1 cup)	64	16

Learn even more about this nutrient by reading the Folate Fact Sheet from the National Institutes of Health, Office of Dietary Supplements.

Vitamin B₁₂

Vitamin B₁₂ is a water-soluble vitamin and an essential part of coenzymes necessary for fat and protein catabolism, for folate coenzyme function, and for hemoglobin synthesis. In addition, vitamin B₁₂ is required for proper nerve functioning. Vitamin B₁₂ works with folate to convert homocysteine into methionine; by preventing a build-up of homocysteine these nutrients help reduce cardiovascular disease risk. An enzyme requiring vitamin B₁₂ is needed by a folate-dependent enzyme to synthesize DNA. Thus, a deficiency in vitamin B₁₂ has similar consequences to health as folate deficiency. In children and adults, vitamin B₁₂ deficiency causes macrocytic anemia; in babies born to vitamin B₁₂-deficient mothers there is an increased risk for neural-tube defects.

In order for the human body to absorb vitamin B₁₂, the stomach, pancreas, and small intestine must be functioning properly. Cells in the stomach secrete a protein called intrinsic factor that is necessary for vitamin B₁₂ absorption, which occurs in the small intestine. Impairment of secretion of this protein can lead to either atrophic gastritis or pernicious anemia. Atrophic gastritis, a condition where there is chronic inflammation of the stomach (often due to an H. pylori  infection or an autoimmune disorder), can lead to reduced stomach acid production and then in turn less vitamin B₁₂ absorption. Atrophic gastritis becomes more common in people over the age of 50. Pernicious anemia, a type of macrocytic anemia, is treated by large oral doses of vitamin B₁₂ or by putting the vitamin under the tongue (sublingual), where it is absorbed into the blood stream without passing through the intestine. In patients that do not respond to oral or sublingual treatment, vitamin B₁₂ is given by injection. Individuals consuming a vegan diet or older than 50 years of age are advised to eat foods fortified with vitamin B₁₂, take vitamin B₁₂ supplements, or receive vitamin B₁₂ injections. There are no known adverse effects related to vitamin B₁₂ toxicity.

The DRIs for vitamin B₁₂ are listed in Table \(\PageIndex{13}\). A Tolerable Upper Intake Level (UL) for vitamin B₁₂ has not been set. Vitamin B₁₂ is naturally found in animal products (Table \(\PageIndex{14}\)).

Table \(\PageIndex{13}\): Dietary Reference Intakes for Vitamin B₁₂¹

Age Group	RDA (mcg/day)
Infants (0–6 months)	0.4*
Infants (7–12 months)	0.5*
Children (1–3 years)	0.9
Children (4–8 years)	1.2
Children (9–13 years)	1.8
Adolescents (14–18 years)	2.4
Adults (> 19 years)	2.4
* denotes Adequate Intake

 

Table \(\PageIndex{14}\): Dietary Sources of Vitamin B₁₂⁸

Food	Vitamin B12 (mcg)	% Daily Value
Rainbow trout, wild (3 ounces)	5.4	225
Salmon (3 ounces)	4.8	200
Tuna, light, canned in water (3 ounces)	2.5	104
Milk, low-fat (1 cup)	1.2	50
Egg (1 large)	0.6	25

Learn even more about this nutrient by reading the Vitamin B₁₂ Fact Sheet from the National Institutes of Health, Office of Dietary Supplements.

B Vitamin Summary

B vitamins are water-soluble and are not stored in significant amounts in the body. Therefore, they must be continuously obtained from the diet. B vitamins are naturally present in numerous foods, and many other foods are enriched with them. In the United States, B-vitamin deficiencies are rare. A summary of the prominent functions of the B vitamins in metabolism and blood function, and their deficiency syndromes is given in Table \(\PageIndex{15}\).

Table \(\PageIndex{15}\): B-Vitamin Functions in Metabolism and Blood, and Deficiency Syndromes

B Vitamin	Function	Deficiency: Signs and Symptoms
B1 (thiamin)	Coenzyme: assists in glucose metabolism, RNA, DNA, and ATP synthesis	Beriberi: fatigue, confusion, movement impairment, swelling, heart failure
B2 (riboflavin)	Coenzyme: assists in glucose, fat and carbohydrate metabolism, electron carrier, other B vitamins are dependent on	Ariboflavinosis: dry scaly skin, mouth inflammation and sores, sore throat, itchy eyes, light sensitivity
B3 (niacin)	Coenzyme: assists in glucose, fat, and protein metabolism, electron carrier	Pellagra: diarrhea, dermatitis, dementia, death
Vitamin B6 (pyridoxine)	Coenzyme; assists in amino-acid synthesis, glycogenolysis, neurotransmitter and hemoglobin synthesis	Muscle weakness, dermatitis, mouth sores, fatigue, confusion
Biotin	Coenzyme; assists in glucose, fat, and protein metabolism, amino-acid synthesis	Muscle weakness, dermatitis, fatigue, hair loss
Folate	Coenzyme; amino acid synthesis, RNA, DNA, and red blood cell synthesis	Diarrhea, mouth sores, confusion, anemia, neural-tube defects
B12 (cobalamin)	Coenzyme; fat and protein catabolism, folate function, red-blood-cell synthesis	Muscle weakness, sore tongue, anemia, nerve damage, neural-tube defects

Vitamin K

Vitamin K is a fat-soluble vitamin. As discussed in Chapter 9, Vitamin K is required for optimal bone metabolism. Vitamin K is also critical for blood function, as it is a coenzyme for enzymes involved in blood clotting. Blood-clotting proteins are continuously circulating in the blood. Upon injury to a blood vessel, platelets stick to the wound forming a plug. The clotting factors circulating close by respond in a series of protein-protein interactions resulting in the formation of the fibrous protein, fibrin, which reinforces the platelet plug. A deficiency in vitamin K causes bleeding disorders. Signs and symptoms include nosebleeds, easy bruising, broken blood vessels, bleeding gums, and heavy menstrual bleeding in women. The function of the anticoagulant drug warfarin is impaired by excess vitamin K intake from supplements. The Adequate Intakes (AIs) for vitamin K are listed in Table \(\PageIndex{16}\). A Tolerable Upper Intake Level (UL) for vitamin K has not been set. Vitamin K is present in many foods and most highly concentrated in green leafy vegetables. Desirable intestinal bacteria also produce vitamin K in the large intestine. See Table \(\PageIndex{17}\) for a list of dietary sources of vitamin K.

Table \(\PageIndex{16}\): Dietary Reference Intakes for Vitamin K¹

Age Group	AI (mcg/day)
Infants (0–6 months)	2.0
Infants (7–12 months)	2.5
Children (1–3 years)	30
Children (4–8 years)	55
Children (9–13 years)	60
Adolescents (14–18 years)	75
Adults (> 19 years)	120 (males), 90 (females)

 

Table \(\PageIndex{17}\): Dietary Sources of Vitamin K⁹

Food	Vitamin K (mcg)	% Daily Value
Natto (3 ounces)	850	708
Collards, frozen, boiled (1/2 cup)	530	442
Spinach, raw (1 cup)	145	121
Broccoli, boiled (1/2 cup)	110	92
Soybeans, roasted (1/2 cup)	43	36
Edamame (1/2 cup)	21	18

Learn even more about this nutrient by reading the Vitamin K Fact Sheet from the National Institutes of Health, Office of Dietary Supplements.

Key Takeaways

• Vitamins play a different kind of role in energy metabolism; they are required as functional parts of enzymes involved in energy release and storage.
• The water-soluble B vitamins are involved as coenzymes in the breakdown of nutrients and in the building of macromolecules, such as protein, RNA, and DNA.
• B-vitamin deficiencies are relatively rare especially in developed countries; although the health consequences can be severe as with folate deficiency during pregnancy and the increased risk of neural-tube defects in offspring.
• The B vitamins, pyridoxine (B₆), folate, and cobalamin (B₁₂) are needed for blood-cell renewal and/or function.
• Vitamin K is necessary for blood clotting.

References

1. Summary Report of the Dietary Reference Intakes. nationalacademies.org. www.nationalacademies.org/our-work/summary-report-of-the-dietary-reference-intakes. Accessed July 4, 2020.
2. Thiamin - Health Professional Fact Sheet. ods.od.nih.gov.https://ods.od.nih.gov/factsheets/Thiamin-HealthProfessional/. Accessed July 4, 2020.
3. Riboflavin - Health Professional Fact Sheet. ods.od.nih.gov.https://ods.od.nih.gov/factsheets/Riboflavin-HealthProfessional/. Accessed July 4, 2020.
4. Niacin - Health Professional Fact Sheet. ods.od.nih.gov.https://ods.od.nih.gov/factsheets/Niacin-HealthProfessional/. Accessed July 4, 2020.
5. Vitamin B₆ - Health Professional Fact Sheet. ods.od.nih.gov.https://ods.od.nih.gov/factsheets/VitaminB6-HealthProfessional/. Accessed July 4, 2020.
6. Biotin - Health Professional Fact Sheet. ods.od.nih.gov.https://ods.od.nih.gov/factsheets/Biotin-HealthProfessional/. Accessed July 4, 2020.
7. Folate - Health Professional Fact Sheet. ods.od.nih.gov.https://ods.od.nih.gov/factsheets/Folate-HealthProfessional/. Accessed July 4, 2020.
8. Vitamin B₁₂ - Health Professional Fact Sheet. ods.od.nih.gov.https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/. Accessed July 4, 2020.
9. Vitamin K - Health Professional Fact Sheet. ods.od.nih.gov.https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/. Accessed July 4, 2020.