Chapter 10: The Water-Soluble Vitamins - B Vitamins and Vitamin C

Comprehensive vocabulary flashcards covering the concepts, coenzymes, metabolic functions, deficiency disorders, clinical signs, and dietary supplement regulations for the water-soluble vitamins (B vitamins and vitamin C).

Bioavailability

The rate at and the extent to which a nutrient is absorbed and used by the body, which depends on digestive efficiency, GI transit time, previous nutrient intake, preparation method, nutrient source, and other foods consumed simultaneously.

Precursors

Vitamins available from foods in an inactive form that can be converted into active vitamins within the body (e.g., beta-carotene is a precursor to vitamin A).

Tolerable Upper Intake Level (UL)

The highest amount of a nutrient that is likely not to harm most healthy people when consumed daily.

Water-Soluble Vitamins

Vitamins (the B-complex vitamins and vitamin C) that are absorbed directly into the blood, circulate freely in fluids, have excess excreted by the kidneys, and must be consumed more regularly.

Fat-Soluble Vitamins

Vitamins (A, D, E, and K) that are absorbed via the lymphatic system, require protein carriers for transport, are stored in the liver and adipose tissue, and can accumulate to toxic levels if consumed in excess.

Dose Levels and Effects Principle

The principle that as nutrient intake increases, the biological effect reaches an optimum at an intermediate dose and then declines, demonstrating that excessive intake can be as harmful as insufficient intake for most nutrients.

Coenzymes

Complex organic molecules that work in tandem with enzymes to enable them to dismantle or synthesize compounds; the vitamin portion allows the chemical reaction to occur, while the remaining portion binds to the enzyme.

Thiamin (Vitamin $B_1$)

A water-soluble B vitamin that forms the active part of the coenzyme TPP (thiamin pyrophosphate), which assists in energy metabolism; exceptionally rich sources include foods in the pork family and grains.

Beriberi

The thiamin-deficiency disease occurring in two forms: 'dry' beriberi, which reflects nervous system damage characterized by muscle weakness in the arms and legs, and 'wet' beriberi, which causes cardiovascular dilation, fluid retention, and edema.

Riboflavin (Vitamin $B_2$)

A water-soluble B vitamin functioning as part of the coenzymes FAD (flavin adenine dinucleotide) and FMN (flavin mononucleotide), both of which accept and donate two hydrogens during energy metabolism.

FAD (Flavin Adenine Dinucleotide)

A riboflavin-derived coenzyme that picks up two hydrogens during the TCA cycle to become $FADH_2$, transporting them to the electron transport chain where two ATP are generated for each $FADH_2$ oxidized.

Niacin (Vitamin $B_3$)

A B vitamin occurring in two chemical forms—nicotinic acid and nicotinamide—that serve in the metabolic coenzymes NAD and NADP; it can be synthesized endogenously from the amino acid tryptophan.

Niacin Equivalent (NE)

The unit of measurement used to express total niacin intake, based on the conversion ratio that $60\,\text{mg}$ of dietary tryptophan yields $1\,\text{mg}$ of niacin.

Pellagra

The severe niacin-deficiency disease characterized by 'the four Ds': diarrhea, dermatitis (scaly skin lesions on areas exposed to sunlight), dementia, and eventually death.

Niacin Flush

A pharmacological reaction caused by large supplemental doses of nicotinic acid that dilates capillaries, resulting in a painful burning, tingling, and itching sensation.

Biotin

A B vitamin required in very small amounts that functions as a coenzyme in the TCA cycle, gluconeogenesis, fatty acid synthesis, and amino acid breakdown; found in egg yolks and synthesized by GI bacteria.

Pantothenic Acid (Vitamin $B_5$)

A water-soluble B vitamin that forms the structural backbone of coenzyme A (CoA), which is involved in key steps of synthesizing lipids, neurotransmitters, steroid hormones, and hemoglobin.

Vitamin $B_6$

A vitamin existing in three forms—pyridoxal, pyridoxine, and pyridoxamine—whose active coenzyme is PLP; high doses ($2\,\text{g}$ daily for 2 months or more) cause neurological damage.

Folate

Also known as folacin or folic acid, a B vitamin whose coenzyme form THF (tetrahydrofolate) transfers 1-carbon units in metabolism, activates vitamin $B_{12}$, synthesizes DNA, and regenerates methionine from homocysteine.

Polyglutamate vs. Monoglutamate Folate

Natural food folate occurs with up to six glutamate units attached (polyglutamate), whereas synthetic folate found in fortified foods and supplements carries a single glutamate molecule (monoglutamate) and is $1.7$-fold more bioavailable.

Dietary Folate Equivalents (DFE)

A measurement standard that accounts for the higher bioavailability of synthetic monoglutamate folate compared to naturally occurring food polyglutamates.

Neural Tube Defects

Severe congenital malformations of the brain and spinal cord (e.g., spina bifida) that arise early in embryonic development and can be prevented by daily maternal supplementation of $400\,\mu\text{g}$ of folate before conception and through the first trimester.

Macrocytic (Megaloblastic) Anemia

Anemia resulting from folate or vitamin $B_{12}$ deficiency, marked by interrupted DNA synthesis that prevents normal cell division, producing large, irregularly shaped red blood cells that often retain nuclei and cannot properly transport oxygen.

Vitamin $B_{12}$ (Cobalamin)

A cobalt-containing vitamin that activates folate by removing a methyl group and maintains the myelin sheath surrounding nerve fibers; the adult RDA is $2.4\,\mu\text{g}$, found almost exclusively in foods of animal origin.

Intrinsic Factor

A glycoprotein secreted by stomach cells that binds to dietary vitamin $B_{12}$ in the stomach, allowing the complex to be recognized and absorbed by specific receptors in the small intestine.

Atrophic Gastritis

A chronic condition damaging the stomach mucosa that reduces stomach acid and intrinsic factor production, often caused by iron deficiency or Helicobacter pylori infection, resulting in impaired vitamin $B_{12}$ absorption.

Pernicious Anemia

A blood disorder caused by the combination of atrophic gastritis and a complete lack of intrinsic factor, preventing adequate absorption of vitamin $B_{12}$.

Choline

An essential nutrient that can be synthesized from methionine and is used by the body to produce the neurotransmitter acetylcholine and the phospholipid lecithin; excessive intake causes life-threatening hypotension.

Inositol and Carnitine

Nonvitamin compounds that can be manufactured by the body: inositol serves as a structural component of cell membranes, while carnitine transports fatty acids into mitochondria.

Glossitis and Cheilosis

Classic clinical signs of B vitamin deficiency; glossitis is inflammation of the tongue that renders it smooth and swollen, whereas cheilosis causes reddened lips and painful cracks at the corners of the mouth.

Free Radical

An unstable, highly reactive molecule bearing one or more unpaired electrons that inflicts oxidative stress and tissue damage unless neutralized by antioxidants.

Ascorbic Acid (Vitamin C)

A water-soluble antioxidant vitamin that protects against oxidative cellular damage by donating two hydrogens and their electrons to free radicals, thereby converting reversibly into dehydroascorbic acid.

Collagen Hydroxylation

The biochemical assembly of collagen fibrils where vitamin C serves as a cofactor by keeping iron in its reduced, active state, enabling the hydroxylation of proline and lysine residues.

Scurvy

The classic vitamin C-deficiency disease characterized by defective collagen synthesis, symmetrical scorbutic gums without infection, pinpoint hemorrhages from spontaneous internal bleeding, bone fragility, and failure of wound healing.

Vitamin C Smoker Requirement

An additional daily recommendation of $35\,\text{mg}$ of vitamin C beyond the baseline RDA, required because the oxidants in cigarette smoke rapidly deplete this antioxidant in the body.

US Pharmacopeia (USP) Seal

A designation on a supplement label certifying that the product contains declared ingredients in stated amounts, dissolves properly in the body, is manufactured under sanitary conditions, and lacks harmful contaminants.

Structure-Function Claim Disclaimer

A mandatory statement accompanying unapproved structure-function claims on dietary supplement containers stating: 'This statement has not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.'

Nutrient Antagonism

An adverse interaction where high doses of one nutrient supplement hinder the absorption or action of another, such as iron hindering zinc absorption, calcium hindering magnesium/iron, and excess vitamin E antagonizing vitamin K.