Fat-Soluble Vitamins Overview

Fat Soluble Vitamins

• Fat-soluble vitamins differ from water-soluble vitamins in their digestion and absorption processes
• They require bile for digestion and absorption
• Fat-soluble vitamins travel through the lymphatic system
• Excesses are stored in the liver and adipose tissues
• They are not readily excreted, increasing the risk of toxicity
• Digestion and absorption follow a similar pathway to dietary fats
• Insoluble in water, packaged into chylomicrons
• Taken up by the liver, and can be stored
• Transported to other tissues via proteins
• Conditions that alter/hinder intestinal or fat absorption limit absorption

Vitamin A

• First fat-soluble vitamin recognized in 1913
• Precursor: beta-carotene
• Three active forms in the body: retinol, retinal, and retinoic acid
• Foods derived from plants provide carotenoids, some of which can be converted to vitamin A
• Carotenoids are pigments that give fruits and vegetables their yellow, orange, and red colors
• Beta-carotene, the most studied carotenoid, can be split to form retinol in the intestine and liver.
• 1 RAE = 1 µg retinol = 12 µg beta-carotene
• Two sources of vitamin A: pre-formed (retinyl ester) and pro-vitamin (beta-carotene)
• Vitamin A is converted to retinol
• Retinol is bound to RBP, then to retinal
• Retinal participates in vision
• Retinoic acid regulates growth
• Vitamin A sources: fortified milk, mango, spinach, carrots, apricots
• Function: vision, maintaining healthy epithelial tissue, reproduction, development, immunity, growth.
• Prevents damage to skin from the sun
• Maintains a clear cornea
• Converts light energy to nerve impulses in the retina
• Visual activity leads to repeated small losses of retinal, needing replenishment

Vitamin A Deficiency

• Large problem in developing countries
• Symptoms may not appear until after depletion of stores (1-2 years healthy adults, sooner for growing children)
• Liver stores 40-90% of total vitamin A
• Associated with adequacy of stores
• Retinol-binding protein (RBP) is important for vitamin transport
• Deficiency risks infectious diseases (like measles)
• Causes night blindness and blindness
• Bitot's spots: abnormal squamous cell proliferation and keratinization of the conjunctiva
• Possible cause of death
• Vitamin A deficiency causes keratinization in the epithelial cells in the skin, causing dry and scaly skin
• Reduced mucus production in the GI tract, decreasing digestion and absorption, and worsening malnutrition

Vitamin A Toxicity

• Develops when binding proteins are loaded
• Vitamin A is free to damage cells
• Concentrated amounts of preformed vitamin A (animal sources, fortified foods, supplements) are most vulnerable in children
• Can cause bone and birth defects

Vitamin D

• Not an essential nutrient (body synthesizes from cholesterol via sunlight)
• Requires two hydroxylation reactions in the liver and kidneys to become active
• Diseases affecting the liver or kidneys can interfere with Vitamin D activation
• Significant in bone making and maintenance
• Assists in calcium and phosphorous absorption, leading to denser and stronger bones
• Vitamin D influences parathyroid hormone levels, which affects vitamin D turnover rate
• Raises blood calcium concentrations in two ways: increase calcium synthesis and decrease calcium excretion
• Protects against cognitive decline in brain and nerve cells
• May protect against heart disease, inflammation, and brain disorders; type 2 diabetes
• There are misconceptions regarding a healthy diet's adequate Vitamin D amounts
• Latitude, season, time of day, cloud cover, skin melanin content, and sunscreen affect UV exposure, influencing Vitamin D synthesis.
• Adequate 5-30 minutes of unprotected sun exposure to face arms, hands, legs between 10 AM and 4 PM leads to sufficient synthesis
• Most people need some exposure to sunlight to maintain adequate Vitamin D levels
• Latitude, season, and time of day affect UV radiation exposure significantly
• Most of the world's population is at a risk for vitamin D deficiency
• Prolonged exposure to sun risks wrinkles and skin cancer, but reduced risks are possible with sunscreen
• Most People in the world meet at least some Vitamin D needs through sunlight exposure.
• Type B UV radiation with a wavelength between 290-320 nanometers penetrates the skin converting 7-dehydrocholesterol into previtamin D3. UVB radiation does not transmit through glass.

Vitamin D Deficiency

• Four contributing factors: lack of sunlight, dark skin, not consuming fortified milk, and lack of breastfeeding with supplementation
• Vitamin D deficiency leads to slower calbindin production.
• With insufficient calbindin, calcium cannot be absorbed adequately through GI tract
• Increases risks for several chronic diseases and osteoporosis- Vitamin D deficient adolescents don't reach their peak bone mass
• In rickets, the bones fail to calcify normally, leading to growth and skeletal abnormalities
• Bowed legs, and beaded ribs are symptoms

Vitamin D Deficiency: Specific Conditions

• Osteomalacia occurs in adults when there's poor bone mineralization
• Bones become increasingly soft, flexible, brittle, and deformed
• Osteoporosis occurs when there is failure to synthesize adequate Vitamin D or insufficient amounts received through foods.
• Leads to loss of calcium from bones and risk for fractures

Vitamin D Toxicity

• Most likely of the vitamins to have toxic effects- usually from supplements-
• Can raise blood calcium concentrations, form kidney stones, and harden blood vessels. Can cause death

Vitamin E

• Two categories: tocopherols (alpha, beta, gamma, delta) and tocotrienols
• Only alpha-tocopherol is maintained in the body
• Antioxidant that stops free radical reactions
• Protects cells and membranes and PUFA
• Dietary fats are necessary for absorption into the body
• Stored in adipose tissue, muscles, and cell membranes in the body
• a-tocopherol only one to have activity in human body
• Performs a key role as an antioxidant in the body
• Absorption requires dietary fats
• Stored in adipose tissue, muscles, and cell membrane of tissues
• Toxicity is rare; UL is 65 times greater than RDA for adults- Extremely high doses interfere with Vitamin K activity, causing hemorrhage
• RDA based on a-tocopherol form only
• Most of dietary vitamin E derives from vegetable oils and foods containing them

Vitamin E Deficiency

• Primary deficiency is rare
• Associated with diseases (specifically fat malabsorption, like cystic fibrosis)
• Prolonged deficiency leads to neuromuscular dysfunction, potentially affecting neurological symptoms
• Effects include split red blood cells as PUFA becomes oxidized, leading to erythrocyte hemolysis

Vitamin K

• Fat-soluble vitamin in two forms: phylloquinone (green leafy vegetables) and menaquinones (some animal foods and bacteria in the GI Tract)
• Plays a key role in blood coagulation (clotting)
• Essential for activation of clotting proteins (like prothrombin)
• Also helps with bone health- important for vitamin D dependent calcium regulation
• Important for blood clotting to help prevent and limit hemorrhaging
• A secondary vitamin K deficiency can occur due to fat absorption failure.
• Some drugs like antibiotics and anticoagulants may disrupt vitamin K synthesis
• Newborn infants often need a single dose of vitamin K at birth because their GI tract bacteria aren't established yet and placental and breast milk concentrations are low.

Vitamin K Toxicity

• Not common; no adverse effects with high intakes
• No set upper limit
• High doses may reduce the effectiveness of anticoagulant drugs

Vitamin and Mineral Supplements

• Healthy children and adults generally don't need Vitamin and Mineral supplements
• Meeting nutrient needs often through a variety of food sources is better
• Not consuming a diverse amount of fortified food may require supplement use.
• Who should not take supplements:
• Men and postmenopausal women (excess iron)
• Smokers (excess beta-carotene)
• Postmenopausal women (excess Vitamin A)
• Surgery patients (excess Vitamin E)
• Supplements are presumed safe until adverse reactions are documented.
• Supplements aren't obligated to meet any safety or effectiveness standards
• Products may not claim to "prevent, cure, diagnose, or mitigate" diseases.

This quiz covers essential information about fat-soluble vitamins, focusing on their sources, roles, and deficiency symptoms. Key topics include Vitamin A, its precursor beta-carotene, and the implications of vitamin deficiencies and toxicities. Test your knowledge on how these vitamins function in the body and their significance for growth and health.