Water-Soluble Vitamins: Energy-Releasing B-Complex Vitamins

Vitamins

A group of organic nutrients required in small quantities for the maintenance of normal metabolic integrity that generally cannot be synthesized by the human body and must be supplied in the diet.

Endogenously Synthesized Vitamins

Vitamins that can be produced within the human body: vitamin D (synthesized in skin upon exposure to sunlight), niacin (synthesized from tryptophan), and vitamin K and biotin (synthesized by gut bacteria).

Energy-Releasing B-Complex Vitamins

The subcategory of water-soluble B vitamins that function primarily as coenzymes in catabolic and energy-yielding pathways, comprising thiamin ($B_1$), riboflavin ($B_2$), niacin ($B_3$), pantothenic acid ($B_5$), pyridoxine ($B_6$), and biotin ($B_7$).

Hematopoietic B-Complex Vitamins

The subcategory of water-soluble B vitamins critical for blood cell development and maturation, consisting of folic acid ($B_9$) and cobalamin / cynacobalamin ($B_{12}$).

Thiamin Diphosphate (TDP)

The biologically active coenzyme form of thiamin (vitamin $B_1$), also known as thiamin pyrophosphate (TPP), essential for oxidative decarboxylation and transketolase reactions.

Thiamin Diphosphotransferase

The specific enzyme responsible for converting free thiamin to its active form, thiamin diphosphate (TDP), within the liver and brain.

Beriberi

A severe chronic deficiency syndrome of thiamin ($B_1$) resulting in neurological and/or cardiovascular symptoms, classified primarily into dry beriberi and wet beriberi.

Dry Beriberi

A chronic form of thiamin ($B_1$) deficiency affecting the nervous system, characterized by peripheral neuropathy, loss of knee and foot reflexes, paresthesia, muscle tenderness, wrist drop, foot drop, and severe emaciation.

Wet Beriberi

A manifestation of thiamin ($B_1$) deficiency affecting the cardiovascular system, characterized by dyspnea, orthopnea, dilatation of the right heart, high-output heart failure, and dependent peripheral edema.

Lactic Acidosis (in Thiamin Deficiency)

A life-threatening complication of thiamin deficiency caused by impaired pyruvate dehydrogenase activity, leading to systemic accumulation of pyruvate and lactate.

Riboflavin (Vitamin $B_2$)

A water-soluble vitamin consisting of an isoalloxazine ring linked to a D-ribitol chain, used as an intense yellow food additive and serving as the precursor for FMN and FAD.

Flavin Coenzymes (FMN and FAD)

Flavin mononucleotide and flavin adenine dinucleotide; active prosthetic groups derived from riboflavin that act as two-electron carriers in oxidoreduction reactions catalyzed by flavoproteins.

Cheilosis

A classical manifestation of riboflavin ($B_2$) deficiency characterized by painful swelling, erythema, and fissuring at the angles of the mouth and on the lips.

Glossitis

Painful inflammation and swelling of the tongue, presenting with a smooth or magenta-colored appearance, typical of riboflavin ($B_2$) deficiency.

Seborrheic Dermatitis

An inflammatory scaling erythematous dermatosis seen in riboflavin ($B_2$) deficiency, predominantly affecting the nasolabial folds, ears, eyelids, scrotum, or labia majora.

Niacin (Vitamin $B_3$)

A water-soluble B vitamin encompassing nicotinic acid and nicotinamide that can be synthesized endogenously from tryptophan, where $60\text{ mg}$ of dietary tryptophan yields $1\text{ mg}$ of niacin in a pathway requiring vitamins $B_1$, $B_2$, and $B_6$.

Active Forms of Niacin ($NAD^+$ and $NADP^+$)

Nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate; essential cofactors in cellular oxidoreduction reactions, reductive fatty acid synthesis (NADPH), and ADP-ribose donors for DNA repair.

Pellagra

A severe deficiency syndrome caused by lack of niacin and tryptophan, classically described by the four Ds: diarrhea, photosensitive dermatitis, dementia (with depressive psychosis), and eventual death.

Secondary Causes of Pellagra

Etiologies independent of primary dietary niacin deficiency, including deficiency of vitamin $B_2$ or $B_6$, carcinoid syndrome (diversion of tryptophan to serotonin), and Hartnup disease (defective tryptophan absorption).

Niacin Toxicity

Adverse clinical manifestations from excessive intake: daily intakes of $\ge 500\text{ mg/day}$ cause diarrhea, easy bruising, and increased bleeding, while high intakes of $\ge 3{,}000\text{ mg/day}$ induce nausea, vomiting, and liver damage.

Pantothenic Acid (Vitamin $B_5$)

A water-soluble vitamin composed of $\beta$-alanine linked to pantoic acid, with a recommended dietary allowance (RDA) of $5\text{ mg/day}$.

Coenzyme A (CoA)

A pantothenic acid-containing coenzyme essential for cellular energy production, the citric acid cycle, $\beta$-oxidation, acetylation reactions, and cholesterol biosynthesis.

Acyl Carrier Protein (ACP)

A pantothenic acid-containing protein that acts as an acyl-group shuttle during fatty acid biosynthesis.

Burning Foot Syndrome

A rare peripheral nerve manifestation characterized by painful burning sensations and numbness in the lower extremities, attributed to pantot