Fat-Soluble Vitamins: E & K Study Notes

Introduction to Fat-Soluble Vitamins E & K

This session, led by Dr. Leah Cub, will review two fat-soluble vitamins: E and K. The discussion will begin with the structure of the cell membrane, followed by the physiological roles, food sources, recommended intake guidelines, and signs and symptoms of deficiency and toxicity for each vitamin. The lecture will conclude with a definition of medication-nutrient interactions and a review of a key interaction.

Cell Membrane Structure

• The cell membrane consists of two layers of phospholipids, forming a phospholipid bilayer.

• The phosphate portion is hydrophilic (water-loving) and faces the aqueous solutions both inside and outside the cell.

• The fatty acid tails are hydrophobic (water-fearing) and face the interior of the bilayer.

• This structure is highly relevant to the antioxidant activity of vitamin E.

Vitamin E: Physiological Roles

• Blood Clot Prevention & Vessel Dilation: Vitamin E increases the production of two distinct enzymes that are involved in both preventing blood clot formation and dilating blood vessels.

• Antioxidant Activity:

  • Vitamin E acts as an antioxidant, neutralizing reactive oxygen species (ROS) produced by normal metabolism.

  • Adequate intake may help prevent conditions related to chronic oxidative stress, such as obesity, cardiovascular disease, and certain cancers.

  • Its antioxidant activity is largely confined to the phospholipid bilayer of the cell membrane, where it is integrated into the phospholipid portion.

Vitamin E: Forms and Biological Activity

• Naturally occurring vitamin E exists in 8 chemical forms.

• Alpha-tocopherol is the only form recognized to meet human requirements, making it the most biologically active.

• Naturally occurring vitamin E: Also known as RRR-alpha-tocopherol, commonly labeled as D-alpha-tocopherol.

• Synthetic vitamin E: Also known as RACK-alpha-tocopherol, commonly labeled as DL-alpha-tocopherol.

• There is ongoing concern within the scientific community regarding high-dose synthetic vitamin E supplementation.

Vitamin E: Requirements and Food Sources

• An RDA (Recommended Dietary Allowance) exists for vitamin E, measured in milligrams (mg) of alpha-tocopherol.

• Conversion to International Units (IU) for food labels:

  • 1 ext{ IU} = 0.67 ext{ mg D-alpha-tocopherol}

  • 1 ext{ IU} = 0.45 ext{ mg DL-alpha-tocopherol}

• Food Sources: Many plant oils are excellent sources. Since fat increases its absorption, these sources are particularly effective.

  • Sunflower oil (and therefore sunflower seeds)

  • Hazelnuts

Vitamin E: Deficiency

• In the US, vitamin E deficiency is relatively rare, estimated at less than 1 ext{%} among the general population by the CDC.

• Individuals with fat malabsorption are at an increased risk of deficiency for all fat-soluble vitamins, including vitamin E, as dietary fat enhances their absorption.

Vitamin E: Toxicity and Supplementation Concerns

• Recent scientific literature suggests that high-dose vitamin E supplementation is associated with increased mortality risk (increased risk of death).

• Considerations when interpreting literature:

  • Often, the form supplemented is the synthetic form, although not always.

  • Most literature shows a correlation rather than a causation relationship.

  • When the causational aspect is discussed, the increased bleeding risk associated with vitamin E supplementation is frequently mentioned. This aligns with vitamin E's role in increasing enzymes that prevent blood clot formation.

• A tolerable upper intake level (UL) has been established for vitamin E due to the increased risk of bleeding and overall increased mortality risk associated with high intakes.

Vitamin K: Physiological Roles

• Blood Clotting: Plays a crucial role in blood clotting by facilitating the function of prothrombin, an inactive protein essential for forming a blood clot.

• Bone Metabolism: Involved in both adding minerals to bone and removing minerals from bone when needed for the bloodstream.

  • Osteocalcin, a protein that facilitates these processes, is highly dependent on vitamin K for its activity.

• Other Proteins: Assists various other proteins throughout the body, an ongoing area of nutrition research.

Vitamin K: Blood Clotting Cascade

• The blood clotting cascade is a series of steps leading to clot formation:

  1. Vitamin K facilitates the conversion of inactive prothrombin to active thrombin. This occurs when adequate vitamin K is consumed.

  2. Concurrently, platelets are formed to assist in clot formation.

  3. Once activated, thrombin facilitates the conversion of inactive fibrinogen to active fibrin.

  4. Fibrin is a sticky protein that forms a mesh-like structure, allowing platelets to gather on it, leading to the formation of a blood clot.

• Vitamin K performs an extremely important function in this cascade.

Vitamin K: Forms, Sources, and Intake

• The term