B COMPLEX GROUP OF VITAMINS

The B complex group of vitamins is a category of vitamins that, although chemically unrelated, are grouped together due to their shared function as coenzymes in cellular activities. Notably, these vitamins do not provide energy directly, but they play crucial roles in the energy production processes of the body.

THIAMINE (VITAMIN B1)

Thiamine, also known as Vitamin B₁, is an essential nutrient involved in energy metabolism.

Coenzyme Form

• The active coenzyme form of thiamine is thiamine pyrophosphate (TPP).

Sources

• Good dietary sources of thiamine include whole grains (such as whole wheat flour and unpolished rice) and yeast.

Physiological Role of Thiamine

• Thiamine is sensitive to heat and can be destroyed through heating processes.
• It plays a pivotal role in several enzymatic reactions:
    - Pyruvate dehydrogenase: This enzyme catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA and carbon dioxide. This process is vital within the Krebs cycle (or citric acid cycle).
    - Alpha-ketoglutarate dehydrogenase: It facilitates the oxidative decarboxylation of alpha-ketoglutarate to succinyl-CoA and CO₂, also contributing to the Krebs cycle.
    - Transketolase: This enzyme is part of the hexose monophosphate shunt pathway of glucose metabolism and utilizes thiamine in its function.
    - Branched-chain alpha-keto acid dehydrogenase: Thiamine pyrophosphate assists in the oxidative decarboxylation of branched-chain amino acids, specifically valine, leucine, and isoleucine.
    - Additionally, thiamine is fundamental for peripheral nerve function.

Deficiency Manifestations of Thiamine

A deficiency in thiamine can lead to several nutritional and psychological disorders.

• Beriberi: A significant nutritional disorder characterized by early symptoms such as anorexia and the accumulation of pyruvic acid and lactic acid due to impaired metabolism. Symptoms can be categorized into:
    - Wet Beriberi: This form features prominent cardiovascular symptoms including edema in the legs and face, and ultimately leads to heart failure and tachycardia (abnormally fast resting heart rate).
    - Dry Beriberi: Here, central nervous system manifestations predominate, leading to peripheral neuritis with sensory disturbances and might result in complete paralysis with no edema.
• Wernicke-Korsakoff Syndrome: Known as cerebral beriberi, this syndrome presents with clinical features associated with encephalopathy such as confusion, memory loss, visual disturbances, ataxia, and psychosis. It is often seen in individuals with severe nutritional deficiencies, particularly alcoholics.
• Lactic acidosis: This condition arises due to the impaired oxidative decarboxylation of pyruvate, resulting in the accumulation of lactic acid in the bloodstream.

RIBOFLAVIN (VITAMIN B2)

Riboflavin (Vitamin B₂) is a water-soluble vitamin that plays a critical role in energy production and metabolism.

Structure of Riboflavin

• Riboflavin is converted into its active coenzyme forms in the body, which are flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), facilitated by ATP.
• The main physiological role of these coenzymes revolves around electron transport in cellular respiration.

Dietary Sources of Riboflavin

• Rich sources of riboflavin include organ meats such as liver, dried yeast, eggs, and whole milk. Other good sources include fish, whole cereals, legumes, and green leafy vegetables.

Coenzyme Activity of Riboflavin

• Riboflavin is involved in various enzymatic processes:
    - It binds with enzymes to form flavoproteins, which are enzymes requiring riboflavin derivatives (FMN and FAD) for their activity.
    - During oxidation processes, FAD accepts two hydrogen atoms from substrates, leading to its reduction to FADH₂.
    - When FADH₂ is oxidized in the electron transport chain, it generates up to 2 ATP molecules.

Riboflavin Deficiency

• Natural deficiency of riboflavin in humans is uncommon, as it can be synthesized by intestinal flora. However, it usually occurs concomitantly with other nutritional deficiencies, such as those found in beriberi and kwashiorkor, which is a severe form of malnutrition arising from protein deficiency, particularly affecting children.
• Symptoms of riboflavin deficiency include:
    - Dermatitis: An inflammatory skin condition characterized by itchy, dry, red, or blistered skin.
    - Glossitis: Inflammation of the tongue, which may appear magenta-colored (smooth and swollen).
    - Cheilosis: Painful, cracked, and red sores located at the corners of the mouth (angular stomatitis).
    - Seborrheic dermatitis: Scaly lesions can appear around the nasolabial folds, ears, and eyelids.