Introduction to Water-Soluble Vitamins

Water-Soluble Vitamins: An Introduction

Learning Objectives

• Review nutrient classifications.

• List the water-soluble vitamins and relevant intake terminology.

• Define terms related to water-soluble vitamin activity (e.g., coenzyme).

• Describe how a coenzyme facilitates enzyme activity.

• Outline populations at risk for water-soluble vitamin deficiency and toxicity.

Nutrient Classifications: The Nutrient Roadmap Revisited

• Nutrients are broadly divided into:

  • Macronutrients: Carbohydrate, protein, and fat.

  • These are kilocalorie-containing (energy-yielding).

  • Micronutrients: Vitamins and minerals.

  • These are not kilocalorie-containing (not energy-yielding), a key differentiator from macronutrients.

• Vitamins are further categorized as:

  • Water-soluble vitamins (focus of this discussion).

  • Fat-soluble vitamins.

• Minerals are further categorized as:

  • Major minerals.

  • Trace minerals.

Terminology for Micronutrient Intake Recommendations

• While Acceptable Macronutrient Distribution Ranges (AMDRs) guide general macronutrient intake, Dietary Reference Intakes (DRIs) guide general micronutrient intake.

• The DRIs are an umbrella term encompassing several specific recommendations:

  • Estimated Average Requirement (EAR): Guides minimum intake recommendations.

  • Recommended Dietary Allowance (RDA):

  • Often used to guide minimum intake for individuals.

  • Implies a large body of scientific literature exists for that micronutrient.

  • Adequate Intake (AI):

  • Can be set instead of an RDA if insufficient scientific literature is available.

  • Still guides minimum intake recommendations.

  • Tolerable Upper Intake Level (UL): Guides maximum intake recommendations to prevent toxicity.

List of Water-Soluble Vitamins

Many water-soluble vitamins have multiple names, often reflecting their different chemical structures during various biochemical processes.

• Thiamin

• Riboflavin

• Niacin

• Biotin

• Pantothenic acid

• Pyridoxine

• Folate

• Vitamin B12

• Vitamin C

Key Terms: Enzymes, Coenzymes, and Co-actors

• Enzymes:

  • Proteins that facilitate (speed up) chemical reactions.

  • They are not changed in the process.

  • They either break down or build substances in the body (e.g., digestive enzymes breaking down macronutrients).

• Coenzymes:

  • Complex organic molecules that work with enzymes.

  • Their primary role is to facilitate the enzyme's activity.

  • Many coenzymes have water-soluble vitamins as part of their structure.

• Co-actors:

  • Have similar functions to coenzymes.

  • While there are chemical differences, for the purposes of this course, they can be discussed interchangeably with coenzymes.

• Water-soluble vitamins' direct involvement:

  • Coenzyme activity: Thiamin, riboflavin, niacin, biotin, pantothenic acid, pyridoxine, and folate.

  • Co-actor activity: Vitamin B12 and vitamin C.

• Overall Role: All water-soluble vitamins facilitate biochemical reactions by participating in either coenzyme or co-actor activity. They act as