Vitamins

Topic 5: Micronutrients

Learning Objectives

• Distinguish between two categories of vitamins:

  • Fat-soluble

  • Water-soluble

• Distinguish between two categories of minerals:

  • Major/Macro minerals

  • Minor/Micro minerals

• Identify food sources of vitamins and minerals.

• Explain factors affecting the bioavailability of minerals.

• Explain the functions of vitamins and minerals to health.

• State dietary recommendations for vitamins and minerals.

• Describe effects of deficiency and toxicity.

Key Concepts

• Types of Vitamins: Fat-soluble vs Water-soluble

• Classification of Minerals: Major minerals vs Trace minerals

• Each vitamin and mineral:

  • Function

  • Food sources

  • Bioavailability

  • Deficiency

  • Toxicity

Definition of Vitamins

Vitamins are organic compounds that are essential nutrients, meaning the body cannot produce enough of them on its own. Inadequate intake can lead to deficiency symptoms. They do not yield energy and are required in small amounts to support specific functions for health and life.

General Facts & Overview

• Organic Nutrients: Contain C-C or C-H bonds (includes carbohydrates, proteins, lipids, vitamins)

• Inorganic Nutrients: Do not contain C-C or C-H bonds (includes minerals, water)

Comparison of Vitamins

• Vitamins differ from carbohydrates, proteins, and lipids as they are individual units and not made up of subunits.

• They assist enzymes in releasing energy from carbs, fats, and proteins but are not energy-yielding themselves.

• Daily intake of vitamins is small, typically measured in mg or μg.

To Qualify as a Vitamin

• The body must be unable to synthesize the compound, and the absence from the diet for a defined period will produce deficiency symptoms.

Vitamins in Foods

• Vitamins are found naturally in fresh foods and can also be added to processed foods as inactive precursors or provitamins, which get converted into their active forms inside the body.

Addition of Vitamins in Foods

• Enrichment: Replacing vitamins lost during processing.

• Fortification: Adding vitamins that are not originally present in a food to prevent deficiencies and balance nutrient profiles.

Bioavailability

Refers to the rate and extent to which a nutrient is absorbed and used by the body, influenced by factors such as digestion efficiency, previous nutrient intake, food consumed, food preparation method, and source of the nutrient.

Toxicity

Some vitamins, especially fat-soluble ones like A & D, can accumulate in the body and lead to toxicity when taken in large amounts. Tolerable Upper Intake Levels have been established to prevent harm.

Classification of Vitamins and Their Functions

• Fat-soluble Vitamins: A, D, E, K

• Water-soluble Vitamins: The B vitamins and Vitamin CDifferences include absorption, storage, retention, and risk of toxicity. Fat-soluble vitamins are stored in the body, while water-soluble vitamins must be consumed regularly to meet requirements.

Vitamin A

• Sources: Preformed vitamin A (animal sources) and provitamin A carotenoids (plant sources).

• Functions: Important for vision, reproduction, cell development, and antioxidant properties.

• Deficiencies: Can lead to night blindness, xerophthalmia, and increased susceptibility to infections.

• Toxicity: Can occur from excessive intake of preformed vitamin A leading to symptoms like headache, liver damage, and bone pain.

Vitamin D

• Sources: Primarily from animal sources and fortifications, also synthesized in the body from sunlight.

• Functions: Promotes cell growth, immune function, and calcium absorption.

• Deficiencies: Can result in rickets in children and osteomalacia in adults.

• Toxicity: Rare but can lead to hypercalcemia and soft tissue calcification.

Vitamin E

• Source: Abundant in vegetable oils, nuts, seeds, and green leafy vegetables.

• Functions: Acts as an antioxidant, protecting unsaturated fats in cell membrane structures.

• Deficiency: Rare, can cause erythrocyte hemolysis in infants.

• Toxicity: Rare but can inhibit vitamin K and affect blood clotting.

Vitamin K

• Sources: Green leafy vegetables, some oils, and bacterial synthesis in the gut.

• Functions: Essential for blood clotting and bone mineralization.

• Deficiency: Rare in adults, but can occur leading to hemorrhage and is a concern for newborns.

• Toxicity: Not common, but high intake can interfere with anticoagulant medications.

Water-Soluble Vitamins

B Vitamins Overview

• Vitamin B1 (Thiamine)

  • Sources: Whole grains, pork, legumes, seeds, and nuts.

  • Bioavailability: Water-soluble nature allows it to be easily absorbed, but cooking can reduce levels in food.

  • Deficiencies: Can result in beriberi and Wernicke-Korsakoff syndrome, characterized by neurological symptoms.

  • Toxicity: Rare due to its water-soluble nature; excess is typically excreted via urine.

• Vitamin B2 (Riboflavin)

  • Sources: Dairy products, eggs, lean meats, green leafy vegetables, and fortified cereals.

  • Bioavailability: Well-absorbed, but absent in significant amounts in most plant foods unless fortified.

  • Deficiencies: Can cause ariboflavinosis, characterized by sore throat, redness, and swelling of the lining of the mouth and throat.

  • Toxicity: No known toxicity; excess is excreted in urine.

• Vitamin B3 (Niacin)

  • Sources: Meat, fish, poultry, enriched and whole-grain breads, and cereals.

  • Bioavailability: Can be synthesized from the amino acid tryptophan, enhancing availability in protein-rich diets.

  • Deficiencies: Leads to pellagra, with symptoms including dermatitis, diarrhea, dementia, and death (the four D's).

  • Toxicity: Excess intake from supplements can cause flushing, gastrointestinal issues, and liver damage.

• Vitamin B5 (Pantothenic Acid)

  • Sources: Chicken, beef, potatoes, oats, and whole grains.

  • Bioavailability: Readily absorbed from both animal and plant food sources.

  • Deficiencies: Rare, but can cause fatigue, irritability, and impaired coordination.

  • Toxicity: No known toxicity; excess amounts are excreted.

• Vitamin B6 (Pyridoxine)

  • Sources: Fish, beef liver, potatoes and other starchy vegetables, and non-citrus fruits.

  • Bioavailability: Easily absorbed but sensitive to processing and cooking.

  • Deficiencies: Can lead to anemia, depression, and confusion.

  • Toxicity: High doses from supplements may cause nerve damage.

• Vitamin B7 (Biotin)

  • Sources: Eggs, fish, meat, seeds, nuts, and certain vegetables like sweet potatoes.

  • Bioavailability: Biotin is well absorbed, while raw egg whites contain avidin, which can inhibit its absorption.

  • Deficiencies: Rare, but can cause symptoms like hair loss, skin rashes, and neurological issues.

  • Toxicity: No known toxicity; excess is typically excreted.

• Vitamin B9 (Folate)

  • Sources: Leafy greens, legumes, seeds, and fortified foods.

  • Bioavailability: Synthetic folic acid (in supplements and fortified foods) is more bioavailable than natural dietary folate.

  • Deficiencies: Can lead to macrocytic anemia and neural tube defects during pregnancy.

  • Toxicity: Excessive amounts can mask vitamin B12 deficiency.

• Vitamin B12 (Cobalamin)

  • Sources: Animal products, meat, dairy, fish, and fortified cereals.

  • Bioavailability: Requires intrinsic factor for absorption; primarily absorbed in the ileum of the intestine.

  • Deficiencies: Can result in pernicious anemia and neurological issues.

  • Toxicity: Rare; no known adverse effects from high intakes.

Deficiency Symptoms

Deficiency symptoms for each vitamin vary but may include muscle weakness, nausea, or anemia while toxicity is rare.

Vitamin C

• Sources: Fruits and vegetables, particularly citrus fruits, strawberries, bell peppers, and broccoli.

• Functions: Essential for collagen synthesis, antioxidant protection, and enhancing iron absorption.

• Deficiencies: Can lead to scurvy, which is characterized by symptoms such as fatigue, gum disease, and skin issues.

• Toxicity: Rare, but excessive intake can cause gastrointestinal disturbances and kidney stones.