13.2: Water-Soluble Vitamins

Water-soluble vitamins are ones that can dissolve in water. They are carried throughout the body into the tissues, but they are not stored in them. They get excreted when they are not needed, which means the body needs to get these more often to utilize them in the body. The water-soluble vitamins are made up of mainly vitamin C and the B complex vitamins.

Vitamin C

Vitamin C is also called ascorbic acid. Vitamin C functions to help with wound healing. It helps form collagen, an important protein in many body tissues. It also is known for aiding in the absorption of iron in the body. Vitamin C is very fragile, so it may be broken down or destroyed easily. Cooking (with high heat and for a long duration) and exposure to oxygen are two common instances where Vitamin C can be destroyed. Scurvy is the deficiency disease associated with vitamin C. Sailors who traveled on long voyages across the sea did not have access to fresh foods while on the water for an extended period of time. The sailors suffered from poor wound healing and bleeding gums, and in fact, many died. It was discovered that sailors who consumed citrus did were healthier and lived. Vitamin C is typically found in citrus, peppers, potatoes, papaya, kiwi, dark green, and yellow vegetables. The RDA for vitamin C is 75 mg for adult women and 90 mg for adult men.

Thiamine (B1)

Thiamine is essential in glucose metabolism. It acts as a cofactor for enzymes that break down glucose for energy production. Additionally, thiamine 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 thiamine. Thiamine deficiency, also known as beriberi, can cause fatigue, confusion, movement impairment, pain in the lower extremities, swelling, and heart failure. It is prevalent in societies whose main dietary staple is white rice. During the processing of white rice, the bran is removed, along with what were called in the early nineteenth century, “accessory factors,” vital for metabolism. Dutch physician Dr. Christiaan Eijkman cured chickens of beriberi by feeding them unpolished rice bran in 1897. The recommended intake for thiamine is 1.1 mg for females and 1.2 mg for males. Thiamine can be found in grains, wheat germ, pork, liver, salmon, black beans, and enriched foods.

Riboflavin (B2)

Riboflavin is an essential component of flavoproteins, coenzymes involved in many metabolic pathways of carbohydrate, lipid, and protein metabolism. Flavoproteins aid in the transfer of electrons in the electron transport chain. Furthermore, the functions of other B-vitamin coenzymes, such as vitamin B6 and folate, are dependent on the actions of flavoproteins. The “flavin” portion of riboflavin gives a bright yellow color to riboflavin, an attribute that helped lead to its discovery as a vitamin. Riboflavin deficiency, sometimes referred to as ariboflavinosis, is often accompanied by other dietary deficiencies (most notably protein) and can be common in people that suffer from alcoholism. Its signs and symptoms include dry, scaly skin, mouth inflammation and sores, sore throat, itchy eyes, and light sensitivity. The recommended intake is 1.1 mg for females and 1.3 mg for males. Riboflavin can be found in beef liver, kidneys, meat, milk, egg, green vegetables, and cheese.

Niacin (B3)

Niacin is a component of the coenzymes NADH and NADPH, which are involved in the breakdown and/or synthesis of carbohydrates, lipids, and proteins. NADH is the predominant electron carrier and transfers electrons to the electron-transport chain to make ATP. NADPH is also required for the anabolic pathways of fatty-acid and cholesterol synthesis. In contrast to other vitamins, niacin can be synthesized by humans from the amino acid tryptophan in an anabolic process requiring enzymes dependent on riboflavin, vitamin B6, and iron. Niacin is made from tryptophan only after tryptophan has met all of its other needs in the body. The contribution of tryptophan-derived niacin to niacin needs in the body varies widely, and a few scientific studies have demonstrated that diets high in tryptophan have minimal effect on niacin deficiency. Niacin deficiency is commonly known as pellagra and is characterized by diarrhea, dermatitis, dementia, and sometimes death. The recommended intake for niacin is 14 mg for women and 16 mg for men daily. Niacin containing foods are peanuts, ready-to-eat cereals, chicken, rice, yeast, and milk.

Pantothenic Acid (B5)

Pantothenic acid forms coenzyme A, which is the main carrier of carbon molecules in a cell. Acetyl-CoA is the carbon carrier of glucose, fatty acids, and amino acids into the citric acid cycle. Coenzyme A is also involved in the synthesis of lipids, cholesterol, and acetylcholine (a neurotransmitter). Vitamin B5 deficiency is exceptionally rare. Signs and symptoms include fatigue, irritability, numbness, muscle pain, and cramps. You may have seen pantothenic acid on many ingredient lists for skin and hair care products; however, there is no good scientific evidence that pantothenic acid improves human skin or hair. The recommended intake for pantothenic acid is 5 mg a day for an adult. Foods containing vitamin B5 are meats, fish, dairy, poultry, grains, and legumes.

Pyroxidine (B6)

Pyroxidine is the coenzyme involved in nitrogen transfer between amino acids and plays a role in 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 anemia, but it is of a different type than that caused by insufficient folate, cobalamin, or iron, although the symptoms are similar. The size of red blood cells 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. The recommended intake for pyroxidine is 1.3 mg per day for an adult. Foods containing vitamin B6 are pork, liver, wheat, corn, yeast, ready-to-eat cereals, banana, sweet potatoes, and avocados.

Cobalamin (B12)

Cobalamin contains cobalt, making it the only vitamin that contains a metal ion. Cobalamin is an essential part of coenzymes. It is necessary for fat and protein catabolism, folate coenzyme function, and hemoglobin synthesis. A folate-dependent enzyme needs an enzyme requiring cobalamin to synthesize DNA. Thus, a cobalamin deficiency has similar consequences to health as folate deficiency. In children and adults, cobalamin deficiency causes macrocytic anemia, and in babies born to cobalamin-deficient mothers, there is an increased risk for neural tube defects. Cells in the stomach secrete a protein called intrinsic factor necessary for cobalamin absorption, which occurs in the small intestine. Impairment of secretion of this protein either caused by an autoimmune disease or by chronic inflammation of the stomach (such as that occurring in some people with H.pylori infection), can lead to the disease pernicious anemia, a type of macrocytic anemia. Vitamin B12 malabsorption is most common in the elderly, who may have impaired digestive organs, a normal consequence of aging. Pernicious anemia is treated by large oral doses of vitamin B12 or by putting the vitamin under the tongue, where it is absorbed into the bloodstream without passing through the intestine. In patients that do not respond to oral or sublingual treatment, vitamin B12 is given by injection. The recommended intake for cobalamin is 2.4 mcg per day for an adult. Foods containing vitamin B12 are animal foods like meat, eggs, and dairy.

Biotin

Biotin is required as a coenzyme in the citric acid cycle and lipid metabolism. It is also required as an enzyme in the synthesis of glucose and some nonessential amino acids. A specific enzyme, biotinidase, is required to release biotin from protein to be absorbed in the gut. Biotin deficiency is rare but can be caused by eating large amounts of egg whites over an extended period of time. This is because a protein in egg whites tightly binds to biotin, making it unavailable for absorption. A rare genetic disease-causing malfunction of the biotinidase enzyme also results in biotin deficiency. Symptoms of biotin deficiency are similar to those of other B vitamins but may also include hair loss when severe. The recommended intake of biotin is 30 mcg a day for adults. Foods that contain biotin are liver, kidney, egg yolk, and yeast.

Folate

Folate is a required coenzyme to synthesize the amino acid methionine and make RNA and DNA. Therefore, rapidly dividing cells are most affected by folate deficiency. Red blood cells, white blood cells, and platelets are continuously being synthesized in the bone marrow from dividing stem cells. A consequence of folate deficiency is 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 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 congenital disabilities. Folate deficiency is causally linked to the development of spina bifida, a neural-tube defect that occurs when the spine does not completely enclose the spinal cord.

Spina bifida can lead to many physical and mental disabilities. Observational studies show that the prevalence of neural-tube defects was decreased after the fortification of enriched cereal grain products with folate in 1996 in the United States compared to before grain products were fortified with folate. Results of clinical trials have demonstrated that neural-tube defects are significantly decreased in the offspring of mothers who began taking folate supplements one month before becoming pregnant and throughout the pregnancy. The RDA for folate is 600 mcg per day for pregnant women and 400 mcg for an adult. Food sources for folate include fortified dry cereal, liver, kidney beans, green leafy vegetables, brussels sprouts, and broccoli.

Summary of the water-soluble vitamins

B Vitamin	Function	Deficiency: Signs and Symptoms
B1 (thiamine)	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
B5 (pantothenic acid)	Coenzyme: assists in glucose, fat, and protein metabolism, cholesterol and neurotransmitter synthesis	Muscle numbness and pain, fatigue, irritability
B6 (pyroxidine)	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

Lets Practice – Water Soluble Vitamins

Match the word in the correct statement.

1. __________ deficiency can lead to spina bifida.
2. Blood clots need __________ to form.
3. __________ is bright yellow.
4. Eating too many egg whites can cause a __________ deficiency.
5. __________ forms coenzyme A.

Vitamin K

Pantothenic acid

Riboflavin

Biotin

Folate

Answer

1. Folate deficiency can lead to spina bifida.
2. Blood clots need Vitamin K to form.
3. Riboflavin is bright yellow.
4. Eating too many egg whites can cause a Biotin deficiency.
5. Pantothenic acid forms coenzyme A.