Overview
This lecture introduces vitamins as essential micronutrients, discusses their characteristics, the concept of antioxidants, and compares fat-soluble and water-soluble vitamins.
Introduction to Vitamins
- Vitamins are the fourth essential nutrient and the first of the micronutrients.
- There are 13 vitamins: 4 fat-soluble (A, D, E, K) and 9 water-soluble.
- Vitamins are organic, contain carbon, and provide no calories.
- They are absorbed intact (no digestion required) but must be released from food.
- Vitamin deficiencies can be marginal (mild) or severe, with mild forms more common in developed countries.
- Vitamins can be destroyed by heat, light, oxidation, and water.
Vitamin Preservation Tips
- Use minimal water when cooking vegetables to prevent vitamin loss.
- Prefer steaming or microwaving over frying to preserve vitamins.
- Add vegetables to boiling water, not cold water.
- Store oils in a dark cabinet and keep produce in a cool environment for best vitamin retention.
Types and Functions of Vitamins
- Provitamins are inactive forms converted to active vitamins in the body; pre-formed vitamins are active when ingested.
- Vitamins often work together, making whole foods better sources than supplements.
- B vitamins act as coenzymes for metabolic reactions, essential for energy metabolism.
Antioxidants and Free Radicals
- Antioxidants (like vitamins C, E, and beta-carotene) neutralize free radicals—unstable molecules that can damage cell DNA and membranes.
- Excess free radicals lead to oxidative stress, contributing to chronic diseases.
- Free radicals come from metabolism, UV exposure, pollution, processed foods, alcohol, and smoking.
- Plant-based foods are rich in antioxidants and phytochemicals.
Fat-Soluble vs. Water-Soluble Vitamins
- Bioavailability is how well a vitamin is absorbed and used; affected by food source and factors like fiber.
- Fat-soluble vitamins (A, D, E, K) are less bioavailable and require bile and fat for absorption; absorbed via the lymphatic system; stored in liver and fat tissue.
- Water-soluble vitamins are more bioavailable, easily absorbed into the bloodstream, and not stored (except B12); excess amounts are excreted in urine.
- Daily intake: fat-soluble vitamins do not need daily intake due to storage, but water-soluble vitamins should be consumed daily.
- Fat-soluble vitamins have a higher risk of toxicity due to storage; toxicity is generally defined as intake over 10 times the RDA.
Key Terms & Definitions
- Micronutrient — a nutrient needed in small amounts for normal body function.
- Provitamin — an inactive vitamin precursor that the body converts to an active form.
- Antioxidant — a compound that neutralizes harmful free radicals.
- Free radical — an unstable molecule that can damage cells.
- Bioavailability — the degree to which a nutrient is absorbed and utilized by the body.
- Fat-soluble vitamins — vitamins A, D, E, K that dissolve in fat and are stored in the body.
- Water-soluble vitamins — vitamins that dissolve in water and are not stored in the body (except B12).
Action Items / Next Steps
- Review textbook sections on vitamin preservation methods.
- Prepare for the next lecture on vitamin A.