3.1 Fat-Soluble Vitamins

Fat-soluble vitamins A, D, E, and K are essential nutrients that dissolve in fat and store in our bodies. They play crucial roles in vision, bone health, immune function, and blood clotting. These vitamins work together to keep us healthy, but their fat-soluble nature means they can accumulate in our bodies.

While these vitamins are vital, both deficiency and excess can cause health issues. Vitamin A deficiency can lead to night blindness, while too much can cause toxicity. Vitamin D is crucial for strong bones, but deficiency is common in people with limited sun exposure. Balancing intake is key for optimal health.

Fat-Soluble Vitamins Overview

Characteristics of Fat-Soluble Vitamins

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• Fat-soluble vitamins dissolve in fat and get stored in fatty tissues and liver for extended periods
• Four main fat-soluble vitamins: A, D, E, and K work together to maintain various bodily functions
• Absorption occurs in small intestine, requires dietary fat for efficient uptake into bloodstream
• Toxicity risk increases due to potential accumulation in fatty tissues, excess intake leads to hypervitaminosis (vitamin poisoning)

Functions and Sources of Vitamin A

• Retinol (preformed vitamin A) found in animal products, carotenoids (provitamin A) in plant sources
• Supports vision by forming rhodopsin in retina, regulates immune system, promotes cell growth and differentiation, aids reproduction
• Animal sources include liver, eggs, dairy products while plant sources encompass orange and yellow fruits, dark green leafy vegetables (carrots, sweet potatoes, spinach)
• RDA measured in Retinol Activity Equivalents (RAE) varies by age and gender

Vitamin D: The Sunshine Vitamin

• Vitamin D2 (ergocalciferol) from plant sources, D3 (cholecalciferol) from animal sources and sunlight exposure
• UVB radiation converts 7-dehydrocholesterol to vitamin D3 in skin, process affected by latitude, season, time of day
• Enhances calcium and phosphorus absorption, maintains bone health, supports immune system function
• Dietary sources include fatty fish (salmon, mackerel), egg yolks, fortified foods (milk, cereals)
• Recommended intake measured in International Units (IU) or micrograms (μg), varies based on age and sun exposure

Vitamin E as an Antioxidant

• Tocopherols and tocotrienols are forms of vitamin E, with alpha-tocopherol being most biologically active
• Acts as powerful antioxidant protecting cell membranes from oxidative damage
• Supports immune system function, participates in cell signaling pathways
• Found in vegetable oils (sunflower, wheat germ), nuts (almonds, hazelnuts), seeds (sunflower seeds), whole grains
• Recommended intake measured in milligrams (mg) of alpha-tocopherol, varies by age and gender

Vitamin K and Blood Clotting

• Phylloquinone (K1) from plant sources, menaquinones (K2) produced by gut bacteria
• Essential for blood clotting by activating coagulation factors, plays role in bone metabolism
• Green leafy vegetables (kale, spinach), vegetable oils, fermented foods (natto) are rich sources
• Recommended intake measured in micrograms (μg), varies by age and gender

Deficiency and Toxicity

Vitamin A Deficiency and Toxicity

• Deficiency leads to night blindness, xerophthalmia (dry eyes), impaired immune function increasing infection risk
• Toxicity (hypervitaminosis A) causes nausea, headache, blurred vision, skin irritation, potential liver damage
• Deficiency risks: individuals with malabsorption disorders, vegans lacking diverse diet
• Toxicity risks: excessive supplement users, Arctic explorers consuming polar bear liver (extremely high in vitamin A)

Vitamin D Deficiency and Toxicity

• Deficiency results in rickets in children (soft, deformed bones), osteomalacia in adults (bone pain, muscle weakness)
• Toxicity (hypervitaminosis D) leads to hypercalcemia, kidney stones, soft tissue calcification
• Deficiency risks: older adults, limited sun exposure, dark skin reducing UV absorption
• Toxicity rare but possible with excessive supplement use, not from sun exposure or food sources

Vitamin E Deficiency and Toxicity

• Deficiency rare in healthy individuals, can cause neurological problems in severe malnutrition cases
• Generally considered safe at high doses, very high intakes may increase bleeding risk
• Deficiency risks: individuals with fat malabsorption disorders (cystic fibrosis, Crohn's disease)
• Toxicity rare, possible with excessive supplement use but not from food sources

Vitamin K Deficiency and Toxicity

• Deficiency impairs blood clotting, increases bleeding risk, may affect bone health
• No known toxicity from food sources, potential interaction with anticoagulant medications (warfarin)
• Deficiency risks: newborns (limited vitamin K transfer through placenta), long-term antibiotic therapy disrupting gut bacteria
• Toxicity not significant concern, caution advised for those on blood thinners due to vitamin K's role in clotting