Vitamin A Roles: Gene Regulation and Cell Differentiation

Roles of Vitamin A

• Hundreds of genes are regulated by the retinoic acid form of vitamin A
• Genes direct the synthesis of proteins that perform the metabolic work of tissues
• Vitamin A affects the metabolic activities of tissues and, in turn, the health of the body

Cell Differentiation

• Vitamin A is needed by all epithelial tissue (external skin and internal linings) such as protective linings of the lungs, intestines, vagina, urinary tract, and bladder
• Cell differentiation is when each type of cell develops to perform a specific function
• Example: When goblet cells mature, they specialize in synthesizing and releasing mucus to protect delicate tissues from toxins or other harmful elements

Roles of Vitamin A - Cell Differentiation

• If vitamin A is deficient, cells fail to make mucus and eventually die off, are displaced with Keratin
• As dead cells accumulate on the surface, the tissue becomes vulnerable to infection
• Examples:
  • Cornea → xerophthalmia
  • In the lungs, the displacement of mucus-producing cells makes respiratory infections likely
  • In the urinary tract → urinary tract infections

Immune Function

• Vitamin A has an "anti-infective" reputation
• With no sufficient Vitamin A, the body's defenses are weakened, and illness can become severe

Reproduction and Growth

• In men: Vitamin A participates in sperm development
• In women: Vitamin A supports normal fetal development during pregnancy
• In the developing embryo: Vitamin A is critical for the formation of the spinal cord, heart, and other organs
• Vitamin A is indispensable for growth; failure to grow is one of the first signs of poor vitamin A status in a child

Vitamin A Deficiency around the world

• An estimated 5 million children suffer from severe vitamin A deficiency
• 190 million more children have impaired immunity, leaving them open to infections

Vitamin A Toxicity

• Can occur when excess vitamin A is taken as supplements or fortified foods
• Pregnant women: especially, should be wary—excessive vitamin A can injure the spinal cord and other tissues of the developing fetus, causing birth defects
• Children: can be easily hurt by vitamin A excesses when they mistake chewable vitamin pills and vitamin-laced gum for treats
• Adolescents: at risk when they take high doses of vitamin A in misguided attempts to cure acne

Vitamin A Recommendations

• DRI for men is 900 micrograms
• DRI for women is 700 micrograms
• Tolerable Upper Intake Level is 3,000 micrograms

Food Sources of Vitamin A

• Active vitamin A is present in foods of animal origin
• Richest sources: liver and fish oil
• Good sources: milk and milk products, and other vitamin A–fortified foods such as enriched cereals
• Beta-carotene is naturally present in many vegetables and fruit varieties

Vitamin K

• The main function of vitamin K is to help activate proteins that help clot the blood
• Also necessary for the synthesis of key bone proteins
• Deficiency: few people have vitamin K deficiency, can be produced by intestinal bacteria
• Newborns need to be given Vitamin K at birth since they are born with a sterile intestinal tract

Vitamin K Toxicity

• Very rare
• No UL set for vitamin K
• However, in infants & pregnant women, vitamin K toxicity can result when supplements of a synthetic version of vitamin K are given → breakage of RBC and their release of their pigments → release of bilirubin by the liver into the blood → Jaundice

The Water-Soluble Vitamins

• Vitamins B & C
• Dissolve in water
• In food, easily dissolve and drain away with cooking water
• Some are destroyed on exposure to light, heat, or oxygen during processing
• In the body, easily absorbed and just as easily excreted in the urine
• A few can remain in the lean tissues for a month or more – but no real storage tissues exist

Roles of Vitamin C

• Assists enzymes involved in the formation and maintenance of collagen
• Participates in the production of carnitine
• Creation of certain hormones
• Antioxidant: protects substances found in foods and in the body from oxidation by being oxidized itself
• Example: Cells of the immune system maintain high levels of vitamin C to protect themselves from free radicals

Vitamin C Supplements

• Can Vitamin C Supplements cure a cold? Research most often fails to support those long-lived beliefs

Vitamin C Deficiency

• Scurvy symptoms are due to collagen breakdown
• Loss of appetite, growth cessation, tenderness to touch, bleeding gums, swollen ankles and wrists, anemia, red spots on skin, and weakness
• Persons at risk of deficiency are: smokers, people addicted to alcohol/drugs, infants fed cow’s milk only and receive no fruit juice and no vitamin C in formulas, and elderly

Explore the essential roles of Vitamin A in regulating genes and facilitating cell differentiation, impacting tissue health and overall bodily functions.