Vitamin A and D PDF

Vitamin A and D by Prof. Dr. Ahmed Ameen Prof. Of Nutrition Fat-soluble Vitamins ◼ Stored in the liver and adipose tissue ◼ Excess may accumulate and cause toxicity ◼ Cases of toxicity with vitamin A and D have been reported ◼ Do not need to be consumed each day du...

Vitamin A and D by Prof. Dr. Ahmed Ameen Prof. Of Nutrition Fat-soluble Vitamins ◼ Stored in the liver and adipose tissue ◼ Excess may accumulate and cause toxicity ◼ Cases of toxicity with vitamin A and D have been reported ◼ Do not need to be consumed each day due to storage in the body ◼ Absorbed slowly with fats ◼ Diseases due to deficiency are rare as large amounts are stored in the body Fat-soluble vitamins are not destroyed by normal cooking methods. They are stable to heat and light. They are destroyed by alkalis, such as baking soda. Some cooks add small amounts of baking soda when cooking vegetables to improve flavors and brighten colors.  Vitamin A from animal sources (Retinol) retinol is readily absorbed from those dietary sources in the small intestine. Three preformed compounds called retinoids that are metabolically active and found in animal products ❖ In the body retinol can be oxidized to retinal or retinoic acid which have 2 specific functions: ❑ Retinal plays a central role in the function of retina. ❑ Retinoic acid helps regulate gene expression and cell development  Vitamin A from plant sources (Provitamin) ◼ Plants do not contain vitamin A, but many dark- green or dark-yellow plants contain carotenoids that are ‘precursors’ of Vitamin A. They can be converted to Vitamin A (retinol) within the intestinal mucosa just prior to absorption. Carotenoids are yellow, orange, and red pigments present in plants. Green vegetables also contain carotenoids, though the pigment is masked by the green pigment of chlorophyll. Beta-carotene is the name of a carotenoid.  Conversion of Carotenoids to Retinoids ◼ Enzymatic conversion of carotenoids occurs in liver or intestinal cells, forming two molecules of retinol and finally retinal and retinoic acids. ◼ Provitamin A carotenoids ❑ Beta-carotene ❑ Alpha carotene ❑ Beta-cryptoxanthin Functions of Vitamin A ◼ Vision ◼ Gene transcription ◼ Immune function ◼ Embryonic development and reproduction ◼ Bone metabolism ◼ Skin health ◼ Antioxidant activity Primary functions of Vitamin A... 1. Maintains and strengthens the skin 2. Maintains health of specialized tissues such as the retina of the eye 3. Maintenance of the mucosal tissues and secretions, which in turn are responsible for normal functioning of the immune system; 4. Normal bone development 5. Maintenance of the reproductive system: required for sperm production in the male and regulate reproductive cycles in the female.  Functions of Vitamin A 1. Vision: Vit. A plays a central role in the transformation of light energy into nerve impulses which perceived by brain as vision. Deficiency: Night blindness Role of Vitamin A in Vision ◼ Normal vision depends on the retina and on adequate vitamin A ◼ In the retina, vitamin A in the form of retinal binds to a protein called opsin to make rhodopsin (in rod cells) and iodopsin (in cone cells) Rhodopsin and iodopsin are light-sensitive pigments Role of Vitamin A in Vision ◼ Retinal turns visual light into nerve signals in retina of eye. ◼ Retinoic acid required for structural components (Cones and Rods) of eye : ❑ Cones in the retina ◼ Responsible for vision under bright lights ◼ Translate objects to color vision ❑ Rods in the retina ◼ Responsible for vision in dim lights ◼ Translate objects to black and white vision Role of Vitamin A in Vision Dark Adaptation time ◼ Bright light depletes rhodopsin ◼ Sudden shift from bright light to darkness causes difficulty in seeing ◼ Rhodopsin is synthesized in a few minutes and vision is improved in the dark ◼ The time required to synthesize rhodopsin in the dark is called dark adaptation time ◼ It is increased in vitamin A deficiency 2. Skin and mucus membrane health : Vit. A promotes proper growth of skin epithelial cells and mucous membranes of the respiratory, gastrointestinal, and genitourinary tracts. Deficiency: Xerosis (mucus-secreting cells are replaced by keratin producing cells) dry skin and dry eye (xerophthalmia). Xerophthalmia Dry Skin CEWG, 2006 Recommended Dietary Allowance (RDA) Vitamin A for Adults ◼ Women: 700 µg or 2,330 IU µg ◼ Men: 900 µg or 3,000 IU ◼ UL Men or Women: 3,000 µg or 10,000 IU Source and Concentration of Vit. A and β-Carotene Foods rich in vitamin A (retinol ) Serving size μg Beef liver 100g 9100 Cod liver oil (very rich source) 10g 2550 Egg 1 whole 110 Others: kidney, dairy products, butter, fortified margarine. Foods rich in β- and other carotenoids Serving size μg Vit. A Carrot 1, large 810 Sweet potato 1, large 920 Spinach and broccoli 100mg 460 Others: red palm oil apricots, peaches, melon, pumpkin.  Vitamin A Deficiency and Diseases ◼ Xerophthalmia (zîr'əf-thăl'mē-ə) is a major cause of preventable blindness in children, especially in developing countries. It is an inflammation of the cornea (the clear covering of the eye). ◼ Night Blindness is a condition making it difficult or impossible to see in dim light. ◼ Vitamin A deficiency causes hardening and roughening of the skin, acne, birth defects, and degeneration of mucous membranes. ◼ Bitot's Spots (′bē·tōs ′späts) are distinct elevated white patches on the conjunctiva, the membrane that covers most of the visible part of the eye. Excess Vitamin A in the diet... Excess Vitamin A is stored in the liver. In a well-nourished person, there may be a 2 - 12 month supply stored at any given time. A large surplus will accumulate in the liver and may be harmful. Such excessive intakes are less likely to result from over-eating than through the over-use of manmade vitamin pills or dietary supplements. Overdoses of manmade Vitamin A is called ‘Hypervitaminosis A’.  PEOPLE AT GREATER RISK OF DEVELOPING VITAMIN A TOXITITY 1.Infants and children are more susceptible than adults to vitamin A toxicity. 2.Vitamin A is a teratogen and high doses (more than 10000 μg retinol) may produce birth defects, even with exposure for 1week in early pregnancy. 3.Pregnant women should avoid excess intake of vitamin A from supplements and from vitamin A- rich foods, such as liver (100 g contains nearly 10000 μg retinol). 4.Daily dose should not exceed 2500 μg during pregnancy or better replaced by cartenoids (their conversion to Vit. A in the body is tightly regulated, thus carotenes do not produce vitamin A toxicity). ◼ Side effects of vitamin A excess/overdose include nausea, itchiness, irritability, vomiting, headaches, menstrual problems, dizziness, pimples, and birth defects. Long term vitamin A overdose can lead to liver damage, pain in the muscles and bone. Signs and Symptoms of Vitamin A toxicity 1. Bone pain and joint swelling. 2.Nausea , vomiting and diarrhea. 3.Dry skin and lips. 4.Hair loss. 5.Headache and blurred vision. 6.Enlargement of the liver and spleen. 7.Reduced thyroid activity. 8.High blood calcium  Vitamin D ◼ Vitamin D is another fat-soluble vitamin. It is essential for maintaining normal calcium metabolism. Vitamin D can be synthesized by humans in the epidermis of the skin upon exposure to ultraviolet-B (UVB) radiation from sunlight, or it can be obtained from the diet. ◼ Vitamin D works hand-in-hand with calcium. Neither can work alone.  Sources of Vitamin D. ◼ As little as 5-10 minutes of sun exposure on arms and legs or face and arms three times weekly between 11:00 am and 2:00 pm during the spring, summer, and fall should provide a light-skinned individual with adequate vitamin D and allow for storage of any excess for use during the winter with minimal risk of skin damage ◼ Vitamin D is found naturally in very few foods: some fatty fish (mackerel, salmon, sardines), fish liver oils, and eggs. In the U.S. and Canada, it is a common nutritional additive to milk, orange juice, and cereals. Check product labels. The “vitamin D winter” extends from mid-October to mid- March in the midwest, and this is the time to take Vitamin D supplements Recommended dietary allowances... The issue of sunlight exposure confounds the existing data on vitamin D requirements, making it impossible to accurately calculate daily needs. The Recommended Dietary Allowances, therefore, have be set with the assumption that no vitamin D is being synthesized in the skin through exposure to sunlight. Life Stage Age Males Females Adolescents 14-50 5 mcg /day 5 mcg /day and adults years 200 IU/day 200 IU/day Adults 51-70 10 mcg /day 10 mcg /day years 400 IU/day 400 IU/day Food Serving Size Vitamin D (mcg) Vitamin D (IU) Pink Salmon 3 ounces 13.3 530 Cow’s milk, 8ounces 2.5 98 fortified with Vitamin D Cereal, enriched 1 serving 1.0-1.3 40-50 Egg yolk 1 large 0.53 21 Primary functions of Vitamin D... 1. Vitamin D is essential for the efficient metabolism and utilization of calcium by the body. Maintenance of calcium levels within a narrow range is vital for normal functioning of the nervous system. 2. Works with calcium for bone growth and maintenance of bone density. 3. Adequate vitamin D levels may be important for decreasing the risk of high blood pressure. 4. Plays a role in insulin secretion under conditions of increased insulin demand. Excess Vitamin D in the diet ◼ Vitamin D toxicity, known as Hypervitaminosis D, induces abnormally high calcium levels (Hypercalcemia), which could result in bone loss, kidney stones, and calcification of organs like the heart and kidneys if untreated over a long period of time. Excessive exposure to sunlight does not lead to vitamin D toxicity. Excesses are usually attributed to overdoses of dietary supplements ◼ Like Vitamin A, a surplus of Vitamin D is stored in the liver and body fat ◼ An individual experiencing vitamin D poisoning may complain of weakness, fatigue, loss of appetite, nausea, and vomiting. In infants and children there may be growth failure 20070912_vitamins Vitamin D deficiency... ◼ In infants and children, severe vitamin D deficiency results in the failure of bone to mineralize, a disease called Rickets. Rapidly growing bones are most severely affected by rickets. The growth plates of bones continue to enlarge, but in the absence of adequate mineralization, weight-bearing limbs (arms and legs) become bowed. ◼ Vitamin D deficiency causes muscle weakness and pain in children and adults. In adults it may develop into osteomalacia, a disease characterized by poorly calcified, softened bones ◼ Vitamin D deficiencies increase the risk of osteoporosis, which is a progressive loss of bone density. Risk Factors for vitamin D deficiency... There are numerous factors that place people at a higher risk of having a vitamin D deficiency: 1. Infants that are exclusively breast-fed 2. Individuals with dark skin, as they don’t synthesize Vitamin D as well as those with light skin 3. Elderly individuals, as they have reduced ability to synthesize Vitamin D when exposed to UVB radiation and they stay indoors more. 4. Individuals covering all exposed skin or using sunscreen whenever outside 5. People with malabsorption syndromes such as cystic fibrosis or cholestatic liver disease 6. People with inflammatory bowel disease, like Crohn’s disease 7. People who are obese. 8. People who live in cloudy climates or cities with contaminated air that may lack sufficient amounts of ultraviolet rays. 9. Individuals who consume mineral oil, and the fat substitute Olestra, as they interfere with absorption of Vitamin D.