Nutrition: Micronutrients and Vitamins Overview

Introduction to Vitamins and Phytochemicals

Vitamins are essential organic compounds that the body requires in small amounts for various physiological functions. They are critical for metabolism, immunity, and overall health. Vitamins are classified into two main categories: water-soluble and fat-soluble. Water-soluble vitamins consist of the B vitamins and vitamin C, while fat-soluble vitamins include vitamins A, D, E, and K.

Much of our understanding of vitamins has been derived from the accidental observations made in humans and animals. For instance, the B vitamins were originally thought to be a single substance but were later identified as numerous distinct compounds. Additionally, phytochemicals, which are non-nutritive compounds found in plants, are not classified as essential but are known to provide various health benefits, such as antioxidant and anti-inflammatory properties.

Importance of Vitamins and Phytochemicals

There are several key reasons why vitamins and phytochemicals are vital to human health:

1. Maintaining Overall Health: Vitamins play essential roles in energy metabolism, immune response, and tissue repair.

2. Preventing Diseases: Certain vitamins, like vitamin C, enhance immune function and reduce infection risk. Vitamin D may lower the risk of osteoporosis and some cancers.

3. Supporting Vital Functions: Vitamins are crucial for functions such as vision, blood clotting, and reducing inflammation.

4. Enhancing Nutrient Absorption: For example, vitamin C enhances the absorption of iron from plant sources.

Sources of Vitamins in Foods

Vitamins can be found in a variety of food sources:

• Whole vegetables and fruits: Rich in several B vitamins, vitamin C, and vitamin A.

• Grains: Whole grains provide a wide range of B vitamins.

• Protein Sources: Include eggs, dairy, meat, and legumes, which are high in thiamin, riboflavin, and other essential vitamins.

• Healthy Fats: Certain oils and nuts are good sources of fat-soluble vitamins.

Fortified and Enriched Foods

Fortification refers to adding nutrients to foods, where those nutrients were not originally present, such as adding calcium to orange juice. Enrichment involves restoring nutrients that were lost due to processing, like adding B vitamins back to white rice. Health Canada regulates which foods must be fortified to help prevent nutritional deficiencies and promote public health.

Digestion and Absorption of Vitamins

The absorption of vitamins occurs primarily in the small intestine:

1. Mouth: Chewing breaks food into smaller particles, releasing vitamins.

2. Stomach: Digestion continues, and some water-soluble vitamins are absorbed here.

3. Gallbladder: Releases bile to emulsify fats for fat-soluble vitamin absorption.

4. Pancreas: Secretes enzymes that aid in vitamin release from food.

5. Small Intestine: Fat-soluble vitamins are incorporated into micelles to be absorbed by diffusion, while water-soluble vitamins are absorbed directly into the bloodstream.

6. Large Intestine: Some bacteria synthesize vitamins, which can also be absorbed.

Bioavailability of Vitamins

For vitamins to exert their effects, they must be adequately absorbed by the body, with absorption rates between 40-90% occurring in the intestine. Bioavailability can be affected by several factors, including:

• Dietary fat: Essential for the absorption of fat-soluble vitamins.

• Transport molecules: Needed for some water-soluble vitamins.

• Inactivity of precursors: Some vitamins exist in precursors that must be activated in the body.

Thiamin (Vitamin B1)

Thiamin, the first B vitamin discovered, is crucial for carbohydrate metabolism and energy production. A deficiency known as beriberi can lead to severe weakness and neurological complications. While thiamin is commonly found in enriched grains, legumes, and nuts, alcoholics are particularly at risk of deficiency due to impaired absorption. Symptoms of low thiamin include fatigue and nerve damage.

Riboflavin (Vitamin B2)

Key sources of riboflavin include dairy products, whole grains, and leafy greens. It plays a pivotal role in energy production, acting as an antioxidant, and maintaining healthy skin and eyes. Riboflavin deficiency, though rare due to fortification, can lead to symptoms such as fatigue and skin disorders.

Niacin (Vitamin B3)

Niacin plays a critical role in energy production and cholesterol management. It was historically linked to the condition pellagra, characterized by dermatitis, diarrhea, and dementia. Unlike other vitamins, niacin can be synthesized from the amino acid tryptophan, making deficiencies less common in a well-balanced diet. High intake of niacin supplements can lead to toxicity, manifesting as elevated blood pressure and liver damage.

Pantothenic Acid (Vitamin B5)

Found abundantly in meat, eggs, and whole grains, pantothenic acid is essential for energy metabolism and hormone synthesis. Deficiencies are rare but can occur as part of broader B vitamin deficiencies.

Vitamin B6

Vitamin B6 is involved in amino acid metabolism and neurotransmitter synthesis, with deficiencies leading to symptoms such as anemia and neurological issues. Overuse of supplements can lead to toxicity, though this is uncommon.

Folate (Vitamin B9)

Folate is crucial for DNA synthesis and is especially important during pregnancy to reduce neural tube defect risks. While fortification has helped reduce deficiency rates, concerns have been raised regarding potential links to increased cancer risk due to excessive folate.

Vitamin B12

Essential for DNA synthesis and red blood cell formation, vitamin B12 is primarily found in animal products. Deficiencies can occur in vegans and individuals with absorption issues, leading to significant health concerns such as anemia and neurological disorders.

Vitamin C

Known for its antioxidant properties, vitamin C supports immune function and collagen production. While deficiencies are rare, severe cases can result in scurvy. Many Canadians use vitamin C supplements, but research suggests they do not effectively prevent the common cold.

Fat-Soluble Vitamins Overview

Fat-soluble vitamins (A, D, E, K) are absorbed along with dietary fat and can be stored in body fat, which raises the potential risks of toxicity from high intake. Key functions include vision health (vitamin A), calcium absorption (vitamin D), and blood clotting (vitamin K). Dietary sources vary, but common ones include leafy greens and fortified foods. Toxicity is usually a concern with supplements rather than from natural food sources.

In summary, vitamins are crucial for maintaining health, supporting vital bodily functions, and preventing nutritional deficiencies. A well-rounded diet rich in fruits, vegetables, whole grains, and lean proteins is typically the best way to ensure adequate vitamin intake.