THE CONTEXT
Vitamins are organic nutrients needed in small quantities for biochemical functions. They generally cannot be synthesized by the body and therefore require dietary supply.
Lipid-soluble vitamin absorption and transport
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Lipid-soluble vitamins are hydrophobic and require normal fat absorption for efficient absorption.
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They circulate in lipoproteins or attached to specific binding proteins.
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Dietary inadequacy, very-low-fat diets, steatorrhea, and biliary disorders can lead to deficiencies by limiting supply or interfering with digestion and absorption.
Lipid-soluble vitamin functions and deficiencies
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Vitamin A supports vision and cell differentiation; deficiency causes night blindness and xerophthalmia.
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Vitamin D supports calcium and phosphate metabolism and cell differentiation; deficiency causes rickets in young children and osteomalacia in adults.
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Vitamin E acts as an antioxidant; deficiency is associated with neurologic disorders and hemolytic anemia of the newborn.
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Vitamin K supports blood clotting; deficiency is associated with hemorrhagic disease of the newborn.
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Excessive intake of vitamins A and D can cause toxicity.
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Vitamin A, carotenes, and vitamin E have antioxidant activity and possible roles in preventing atherosclerosis and cancer, but in excess may act as damaging pro-oxidants.
Water-soluble vitamin functions and deficiencies
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The water-soluble vitamins listed are vitamins B and C, folic acid, biotin, and pantothenic acid. Their main functions are as enzyme cofactors.
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Folic acid carries one-carbon units.
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Isolated deficiency of one B-complex vitamin is rare because poor diets commonly produce multiple deficiencies.
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Thiamin deficiency causes beriberi; riboflavin deficiency causes cheilosis, glossitis, and seborrhea; niacin deficiency causes pellagra.
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Vitamin B12 deficiency is associated with megaloblastic anemia, methylmalonic aciduria, and pernicious anemia.
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Folic acid deficiency is associated with megaloblastic anemia, while vitamin C deficiency causes scurvy.
Dietary mineral requirements
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Inorganic mineral elements with bodily functions must be supplied in the diet.
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Insufficient iron intake can cause anemia, while insufficient iodine intake can cause cretinism and goiter.
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Excessive mineral intakes may be toxic.