Introduction to Vitamins

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Image : “Medicine” by PIXNIO. License: Public Domain

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Overview

There are 13 vitamins in total that a human body needs. They are as follows:

1. Vitamin A
   • B vitamins:
2. Vitamin B1 – Thiamine
3. Vitamin B2 – Riboflavin
4. Vitamin B3 –  Niacin
5. Vitamin B5 – Pantothenic acid
6. Vitamin B6 – Pyridoxine
7. Vitamin B7 – Biotin
8. Vitamin B9 – Folate (Folic Acid)
9. Vitamin B12 – Cobalamin
10. Vitamin C
11. Vitamin D
12. Vitamin E
13. Vitamin K

They are classified based on the biological and chemical activity that they perform. They are classified as:

• Fat-soluble (vitamins A, D, E, and K)
• Water-soluble (B vitamins, vitamin C and vitamin A in its beta-carotene form)

Fat-soluble vitamins are hydrophobic and lipid-soluble. They travel to the general body circulation through the lymphatics of small intestine absorbed in fat globules known as the chylomicrons. These are easily stored in the body.

Therefore, an increased intake of fat-soluble vitamins predisposes a person to hypervitaminosis. Main storage sites are liver and fat tissue. Only a small quantity of these vitamins is required, but a deficiency can lead to certain diseases, such as rickets.

Digestion of these vitamins is by the pancreatic enzymes. Absorption of fat-soluble vitamins requires adequate liver and pancreatic secretions. Too much fat in the stool, i.e., steatorrhea can be caused by:

• Pancreatitis
• Pancreatic cancer
• Liver disease
• Crohn’s disease
• Celiac disease
• Cystic fibrosis
• Gallstones

Common causes of steatorrhea

Basically, anything that reduces enzymes secretion from THE pancreas leads to steatorrhea.

Water-soluble vitamins cannot be stored in the body, and a daily intake of these vitamins is necessary. They are hydrophilic and dissolve in the body where they travel freely. Any excess of these vitamins is simply excreted by the kidneys and later via urine; therefore, toxicity is less common.

Vitamin A – Retinol, Retinoic Acid, Retinal

It is a name referring to many molecules such as Retinol, Retinoic Acid, and Retinal. They are all known as retinoids. It is found in fruits and vegetables as pro-vitamin A carotenoid.

• Dietary source: butter, milk, cheese, egg yolk, tomatoes, carrots, spinach, mangoes, and corn
• Daily requirement: 400 µg for 2,000 calorie intake
• There is a higher requirement for growing children, pregnant women, and in hepatic disease.

Functions

• Role in a vision: rhodopsin has a role in night vision, and retinal is a part of it
• Role in epithelialization: it prevents keratinization of epithelial cells
• Helps in bone and teeth formation
• Required for growth
• Plays a role in the metabolism of DNA and protein synthesis
• Skin becomes dry and scaly in a deficiency of vitamin A

Therapeutic uses

• Oral leukoplakia
• Acute myeloid leukemia
• Acne

Deficiency

• Nyctalopia (poor night vision)
• Dry and scaly skin
• Decreased endochondral bone formation and osteoblastic activity

Toxicity

• Nausea
• Headaches
• Irritability
• Teratogenicity
• Skin and hair problems

Vitamin E – Tocopherols

It refers to a group of compounds that include tocopherols and tocotrienols. Of all the types ƴ-tocopherol is the most common in the diet while α-tocopherol is the most active type.

• Dietary source: wheat, sunflower, grape seed, canola, almond, margarine, cottonseed oil, spinach, and corn oil
• Daily requirement: 10 mg for 2,000 calorie intake
• There is a higher requirement in pregnancy and lactation

Functions

• It has antioxidant properties and contributes to the oxidation of free fatty acids.
• Involved in aerobic cellular respiration
• Combines with reactive oxygen species and works in conjugation with vitamin C
• More oxygen to RBCs

Therapeutic uses

• Nocturnal muscle cramps
• Atherosclerosis
• Fibrocystic breast disease
• Intermittent claudication

Deficiency

• Hemolytic anemia
• Muscular dystrophy
• Hepatic necrosis
• Immune impairment

Excessive intake

• Interferes with vitamin K and impacts clotting. Consider to be synergistic with warfarin and can lead to blood loss
• May can increase in oxidant activity, cell breakdown and increased mortality in cancer
• Leads to vitamin K deficiency due to inhibition in the synthesis

Vitamin K – Quinone

• Dietary source: fish, meat, broccoli, parsley, lettuce, kale, collards
• It is synthesized in the body by the normal intestinal flora. Newborns cannot produce vitamin K due to the sterile gut
• Daily requirement: 80 µg for 2,000 calorie intake

Functions

• Promotes blood coagulation. Factor II, VII, IX, and X require vitamin K
• It is an important co-factor in oxidative phosphorylation
• It enhances the capacity of calcium-binding proteins to deposit calcium in the concerned tissues
• Deficiency: There is a rare chance of deficiency. Prolonged use of antibiotics and other drugs such as warfarin

Vitamin D – Calciferol, Calcitriol

• Dietary source: fish liver oil, egg yolk, margarine, lard
• Daily requirement: 5 µg for 2,000 calorie intake. Sun exposure is very important for conversion into an active form.
• There is a higher requirement in infants, children, pregnant and lactating women.

Activation

From the surface of the skin, 7-dehydrocholesterol is converted into cholecalciferol (vitamin D3) in the presence of sunlight. It then combines with vitamin D2 (ergocalciferol) and gets converted to 25-hydroxyvitamin D3 (calcidiol) in the liver. A process is known as hydroxylation that is further carried out in the kidney to convert it into 1,25-dihydroxy vitamin D3 (calcitriol). This is the active form.

Functions

• Absorption of calcium and phosphate from the intestines
• Enhanced mineralization of the bones
• Absorption of calcium and phosphate from the renal system
• Vitamin D lowers the pH in the colon
• It has a role in increasing the citrate content of blood and bones
  

  Image: “Vitamin D deficiency causes rickets in children.” by http://wellcomeimages.org/indexplus/obf_images/41/45/54127c3cb9dbd83c3e5ca87e90e6.jpg Gallery: http://wellcomeimages.org/indexplus/image/L0014375.html License: CC BY 4.0

Deficiency

• Rickets in children
• Osteomalacia in adults
• Renal osteodystrophy

Toxicity

Hypervitaminosis D occurs if it is taken in large doses, 500 times that of the normal dose. Toxicity produces immediate and delayed effects.

• Immediate effects: anorexia, constipation, lassitude, thirst, polyuria, nausea, vomiting, diarrhea
• Delayed effects: metastatic calcification, urinary lithiasis

Vitamin B1 – Thiamine

• Dietary source: rice, peas, beans, whole white bread, bran, prunes, nuts, liver, meat, eggs, and milk. It is also synthesized by the intestinal flora
• Daily requirement: 1.4 mg. This is related to the carbohydrate content taken in the diet, not the caloric value of food
• Dietary requirements increase in the case of hemorrhage, increased alcohol intake, prolonged illness and the use of antibiotics, increased caloric burnout, fever, hyperthyroidism and pregnancy and lactation.

Functions

• It is a coenzyme in multiple metabolic reactions of the body, e.g., oxidative decarboxylation, the trans-ketolation reaction in glucose metabolism, etc.
• Required for the activity of enzyme tryptophan pyrolyse (tryptophan metabolism)

Deficiency

Deficiency is rare due to the wide distribution of foods. Beriberi is the result of thiamine deficiency. It has the following three types:

1. Dry Beriberi
   • Symmetrical muscle wasting
   • Peripheral neuropathy
   • Confusion
   • Difficulty in speech
   • Involuntary eye movements

2. Wet Beriberi
   • Signs and symptoms of dry Beriberi, along with shortness of breath, rapid heart rate, edema in lower legs and cardiac failure.

3. Wernicke-Korsakoff
   • Confusion
   • Nystagmus
   • Ataxia
   • Confabulation
   • Mammary body damage
   • Aphasia

Vitamin B2 – Riboflavin

• Dietary source: yeasts, beans, peas, green vegetables, nuts, liver, kidney, milk, crab meat, and eggs
• Daily requirement: 1.6 mg for 2,000 calorie intake
• There is a higher requirement in the case of burns, acute illness, broad-spectrum antibiotics use, pregnancy, and lactation.

Functions

• Acts as a coenzyme in certain H-transfer reactions in the metabolism
• Red blood cell production

Deficiency

Vitamin B2 deficiency is rare but may manifest as the following:

• Stomatitis
• Chapped and fissured lips
• Angular stomatitis
• Scaly skin rashes (scrotum, nasolabial folds, vulva)
• Photophobia
• Normochromic normocytic anemia

Vitamin B3 – Niacin

• Dietary source: liver, meat, fish, kidney, legumes, coffee, tea and nuts
• It is also synthesized from tryptophan and in a limited amount by the gut flora.
• Daily requirement: 18 mg for 2,000 calorie intake
• There is a higher requirement in illness, infection, high corn or maize diet, pregnancy, and lactation.

Functions

• Synthesis and formation of NAD⁺ and NADP which further act as co-enzymes in different metabolic reactions
• Nicotinamide formation
• Cholesterol production
• Nerve function

Deficiency

• Dermatitis
• Diarrhea
• Dementia: It can result from B3 or tryptophan. It results in a disease called Pellagra. The following are the clinical features of Pellagra which are known as the 4Ds of pellagra
• Death

Therapeutic use

• To treat high cholesterol

Toxicity

• Skin irritation
• Liver damage
• Flushing of skin

Vitamin B5 – Pantothenic Acid

• Dietary source: kidney, yeast, egg yolk, liver, skimmed milk, chicken, royal jelly (richest source) and molasses
• Daily requirement: 6 mg for 2,000 calorie intake
• There is a higher requirement in case of burns, acute illness, severe injury, use of broad-spectrum antibiotics, growing children, in convalescence, pregnancy, and lactation

Functions

• Formation of active acetate, acetyl Co-A
• Formation of succinyl Co-A which is involved in heme synthesis and degradation of ketone bodies
• Involved in the oxidation of fatty acids
• Plays a role in adrenal cortical function

Deficiency

It is rarely seen due to the wide distribution in food and its supply and synthesis by the gut flora but can lead to burning feet syndrome.

Vitamin B6 – Pyridoxine

• Dietary source: yeast, rice polishings, egg yolk, royal jelly, and cereal grains
• Daily requirement: 2 mg for 2,000 calorie intake
• There is a higher requirement in the second half of pregnancy and in antituberculous treatment with isoniazid

Functions

• Co-enzyme in transamination reaction and decarboxylation reactions
• Co-enzyme for deaminases and kynureninase
• Takes part in the transsulfuration
• Co-enzyme for desulfhydrase
• Neurotransmitter production
• Protein metabolism (transaminases)
• Production of RBCs

Therapeutic uses

• Morning sickness of pregnancy
• Muscular dystrophies
• Hyperoxaluria
• Recurring oxalate stones of the kidney
• Radiation sickness

Deficiency

The deficiency of vitamin B6 does not cause any disease, but the following clinical manifestations are seen:

• Decreased immunity
• Oxaluria
• Peripheral neuropathy
• Epileptiform convulsions in infants
• Anemia

Most common cause of deficiency is isoniazid treatment.

Vitamin B7 – Biotin

• Dietary source: liver, milk, kidney, milk products, molasses, legumes, vegetables and royal jelly. Bacterial flora of intestines can also synthesize this vitamin.
• Daily requirement: 30 µg for 2,000 calorie intake
• There is a higher requirement in pregnancy and lactation and long-term antibiotic therapy.

Functions

• It is a coenzyme for carboxylases enzyme
• Involved in CO₂ fixation reactions
• Fatty acid metabolism
• Cellular growth
• RBC production

Deficiency

There is no specific deficiency disease, but two conditions are related to biotin deficiency. These are:

• Genetic deficiency of holocarboxylase synthase
• Leiner’s disease

Vitamin B9 – Folate (Folic Acid)

• Dietary source: liver, kidney, yeast, green leafy vegetables, cauliflower, spinach, wheat, meat, and fish
• Daily requirement: 400 µg for 2,000 calorie intake
• There is a higher requirement in pregnancy and lactation, cancers and hemolytic anemia.

Functions

• Role in one-carbon metabolism reactions. One carbon moiety can be utilized to form several compounds
• An important role in hematopoiesis
• Myelination
• DNA nucleotide production

Deficiency

• Macrocytic anemia
• Weakness
• Growth retardation
• Granulocytopenia
• Thrombocytopenia
• Megaloblastic anemia (decreased RBCs and hematocrit, increased homocysteine levels, increased MCV)
• Trimethoprim and methotrexate are the drugs that inhibit folate production

Excessive intake

• Vitamin B12 deficiency
• Renal damage

Vitamin B12 – Cobalamin

• Dietary source: liver, fish, egg, meat, and kidney. It is not present in plants
• Daily requirement: 6 µg for 2,000 calorie intake
• There is a higher requirement in pregnancy, lactation and pernicious anemia

Absorption

Stomach acid and digestive enzymes are necessary to remove vitamin B12 from proteins. It then binds to intrinsic factor released by parietal cells of the stomach. Intrinsic factor chaperones B₁₂ to the terminal ileum where it is absorbed.

Functions

• Important for the conversion of homocysteine to methionine
• Nerve cell function
• RBCs production
• Fatty acid oxidation

Deficiency

It is due to the following factors:

• Pernicious anemia (an autoimmune disease affecting parietal cells)
• Metformin use
• Crohn’s disease
• Bowel resection
• Use of antacid and proton pump inhibitors

Deficiency of B₁₂ leads to megaloblastic anemia because folate cannot be recycled.

Nervous system issues arise because of methylmalonic acid which causes demyelination. Peripheral numbness, spasticity, and loss of proprioception are seen in the case of deficiency.

Vitamin C – Ascorbic Acid

• Dietary source: citrus fruits, papaya, pineapple, banana, strawberry, cabbage, cauliflower, green peas, tomatoes, and potatoes. Amla has the highest concentration of vitamin C.
• Daily requirement: 75 mg for 2,000 calorie intake
• There is a higher requirement during infections

Functions

• Involved in cellular oxidation-reduction reactions
• Important for collagen synthesis
• Required for the activity of osteoblasts and fibroblasts
• Cofactor in the hydroxylation of tryptophan
• Tyrosine metabolism
• Helps in the maturation of RBCs along with folic acid
• Formation of tissue ferritin
• Iron absorption
• Important in the electron transport system of the body
• Actives arginase and papain enzymes and inhibits beta-amylase and urease activity
• Co-enzyme for dopamine hydroxylase
• Carnitine formation in the liver
• Fatty acids alpha-oxidation
• Plays an important role during stress

Therapeutic uses

• Treatment of scurvy
• Methaemoglobinaemia
• Wound healing
• Treatment of infectious diseases

Deficiency

A low intake of vitamin C leads to a disease known as scurvy. It has the following clinical manifestations:

• Delayed wound healing
• Poor dentine formation
• Fragile capillaries
• Swollen and bleeding gums
• Poorly laid osteoid of bone
• Hypochromic microcytic anemia
• Painful swelling of joints and bones
• Loose teeth
• Bruising