MN17 - Lipid-Soluble Vitamins

What are the lipid-soluble vitamins?

Vitamins A, D, E, and K.

What are key characteristics of lipid-soluble vitamins?

They are absorbed with dietary fat, require bile salts and pancreatic enzymes, are stored in liver and adipose tissue, and have a higher risk of toxicity.

What conditions commonly cause deficiency of lipid-soluble vitamins?

Malabsorption, liver disease, pancreatic disease, bariatric surgery, and alcoholism.

What forms is vitamin A consumed in?

Retinol and retinyl esters from animal sources and beta-carotene from plant sources.

What happens during vitamin A absorption in the small intestine?

Bile salts emulsify fats, pancreatic enzymes break down retinyl esters, vitamin A is incorporated into micelles and absorbed into intestinal epithelial cells.

What happens to vitamin A inside intestinal cells?

Retinol is converted to retinyl esters and packaged into chylomicrons.

How is vitamin A transported after absorption?

Chylomicrons enter the lymphatic system, then bloodstream, then liver.

Where is vitamin A stored?

About 90% is stored in the liver as retinyl esters, with smaller amounts in adipose tissue and retina.

What role does the liver play in vitamin A metabolism?

Storage, release, and regulation of vitamin A levels.

What are causes of vitamin A deficiency related to absorption?

Cystic fibrosis, Crohn’s disease, celiac disease, chronic pancreatitis, pancreatic insufficiency, gallbladder disease, bile duct obstruction, bariatric surgery, and fat malabsorption syndromes.

What conditions affect vitamin A storage?

Liver disease, alcoholism, cirrhosis, hepatitis, protein malnutrition, and zinc deficiency.

What is vitamin A’s role in the visual system?

11-cis retinal combines with opsin to form rhodopsin, enabling phototransduction and night vision.

What is vitamin A’s role in the ocular surface?

Maintains conjunctival and corneal epithelium, goblet cells, and tear film mucin layer.

What is vitamin A’s role in immune function?

Prevents infection and maintains epithelial tissue.

What are the steps of the visual cycle involving vitamin A?

Retinol converts to retinal, retinal combines with opsin to form rhodopsin, light converts 11-cis retinal to all-trans retinal, phototransduction occurs, signal is sent to brain, retinal is recycled in the retinal pigment epithelium.

What happens to vision in vitamin A deficiency?

Rhodopsin cannot regenerate, leading to night blindness.

What are ocular signs of vitamin A deficiency?

Night blindness, xerophthalmia, Bitot spots, conjunctival keratinization, dry eye, corneal ulcer, keratomalacia, poor epithelial healing, and increased infection risk.

What are systemic signs of vitamin A deficiency?

Dry skin, frequent infections, and growth delay.

What are symptoms of vitamin A toxicity?

Headache, blurred vision, dizziness, liver damage, bone pain, pseudotumor cerebri, papilledema, and teratogenic effects.

When should vitamin A deficiency be suspected clinically?

In dry eye, night blindness, bariatric surgery, liver disease, alcoholism, malnutrition, malabsorption, corneal disease, and poor healing.

What patient care steps should be taken for suspected vitamin A deficiency?

Assess diet, ask about GI disease or surgery, refer to PCP, provide nutritional counseling, supplement if needed, and manage ocular surface disease.

What are key points about vitamin A transport?

It is transported in blood via retinol-binding protein and requires fat absorption mechanisms.

What are sources of vitamin D?

Sunlight (UVB), fatty fish, egg yolks, fortified milk, and supplements.

Where is vitamin D stored?

In fat tissue and liver and released slowly.

How is vitamin D activated?

UVB converts 7-dehydrocholesterol to vitamin D3 in skin, liver converts it to 25-hydroxyvitamin D, and kidneys convert it to active calcitriol.

What are functions of vitamin D?

Increases calcium and phosphate absorption, promotes bone mineralization, maintains bone strength, supports muscle function, regulates immune system, and has anti-inflammatory effects.

What causes vitamin D deficiency?

Limited sun exposure, malabsorption, kidney disease, liver disease, obesity, aging, and poor diet.

What conditions result from vitamin D deficiency?

Rickets, osteomalacia, osteoporosis, bone pain, muscle weakness, fracture risk, and fatigue.

Who is at risk for vitamin D deficiency?

Elderly, dark-skinned individuals, indoor lifestyles, chronic illness, malabsorption disorders, and kidney disease.

What ocular diseases are associated with vitamin D deficiency?

Dry eye disease, age-related macular degeneration, diabetic retinopathy, myopia progression, and inflammatory ocular disease.

What are symptoms of vitamin D toxicity?

Hypercalcemia, kidney stones, confusion, muscle weakness, nausea, arrhythmias, and tissue calcification.

What is the main cause of vitamin D toxicity?

Excess supplementation, not sunlight exposure.

How is vitamin E absorbed and transported?

Absorbed with fat, requires bile salts and pancreatic enzymes, stored in fat and liver, and transported via lipoproteins.

What causes vitamin E deficiency?

Fat malabsorption conditions.

What are the functions of vitamin E?

Acts as a major antioxidant, protects cell membranes, prevents lipid peroxidation, and protects retina, photoreceptors, nervous system, and red blood cells.

What are causes of vitamin E deficiency?

Cystic fibrosis, Crohn’s disease, celiac disease, pancreatic disease, liver disease, and prematurity.

What are symptoms of vitamin E deficiency?

Peripheral neuropathy, ataxia, muscle weakness, hemolytic anemia, retinopathy, and vision problems.

Who is at risk for vitamin E deficiency?

Premature infants and individuals with fat malabsorption disorders.

What is the ocular relevance of vitamin E?

Protects against retinal oxidative stress, supports photoreceptors, helps prevent AMD, and provides neuroprotection.

How is vitamin K absorbed and stored?

Absorbed with fat, requires bile salts, produced by gut bacteria, stored in the liver, and used for clotting factor production.

What are the functions of vitamin K?

Required for synthesis of clotting factors II, VII, IX, and X, prevents excessive bleeding, and supports bone metabolism.

What causes vitamin K deficiency?

Liver disease, malabsorption, antibiotic use, warfarin therapy, and newborn status.

What are symptoms of vitamin K deficiency?

Easy bruising, bleeding, hemorrhage, prolonged clotting time, surgical bleeding, and newborn hemorrhage.

Who is at risk for vitamin K deficiency?

Liver disease patients, antibiotic users, malabsorption conditions, and those on warfarin.

What is the ocular relevance of vitamin K deficiency?

Subconjunctival hemorrhage, retinal hemorrhages, vitreous hemorrhage, and increased surgical bleeding risk.

What should optometrists assess regarding vitamin K?

Medication history (anticoagulants), liver disease, and unexplained bleeding disorders.

What are general deficiency patterns of lipid-soluble vitamins?

Vitamin A causes night blindness and xerophthalmia, vitamin D causes rickets and osteomalacia, vitamin E causes neuropathy and hemolysis, and vitamin K causes bleeding disorders.

What are general storage locations of lipid-soluble vitamins?

Vitamin A in liver, vitamin D in fat and liver, vitamin E in fat and liver, and vitamin K in liver.