Vitamins: vital dietary components

• Definition- Essential organic substances needed in small amounts in the diet for normal function, growth and maintenance of the body

• Yield no energy to the body, they often participate in energy-yielding reactions

• A, D, E, K are fat soluble

• B, C are water soluble

• B, K function as parts of coenzymes (compounds that help enzymes function)

• Can’t be synthesized in the human body

• To be classified as a vitamin, a compound must meet criteria

  • Body is unable to synthesize enough of the compound to maintain health

  • Absence of the compound from the diet for a defined period of time produces deficiency symptoms

• Few vitamins have also proved useful in treating several nondeficiency diseases

• These medical applications require administration of mega doses (well above typical human needs for the vitamins

• Mega doses of a form of niacin can be used as part of blood cholesterol-lowering treatment for certain individuals

• Other examples of medical use include forms of vitamin D in the treatment of psoriasis

STORAGE OF VITAMINS IN THE BODY

• Fat-soluble vitamins are not readily excreted from the body

• Excess amounts of the water-soluble vitamins are generally lost from the body quite rapidly, partly because the water in cells dissolves these vitamins and excretes them out of the body via the kidneys

• Water-soluble vitamin B-6 and vitamin B-12 are exceptions

• An occasional lapse in the intake of even water-soluble vitamins generally causes no harm

• Symptoms of a vitamin deficiency occur only when that vitamin is lacking in the diet and body stores are essentially exhausted

• Average person must consume no thiamin for 10 days or no vitamin C for 20-40 days before developing the first symptoms of deficiency of these vitamins

VITAMIN TOXICITY

• Fat-soluble vitamins can easily accumulate in the body and cause toxic effects

• Toxicities of the fat-soluble vitamin A is the most frequently observed

• ‘one-a-day’ type of multivitamin and mineral supplement usually contains less than 2 times the Daily Values of the components regular use of these products is unlikely to cause toxic effects in men

• but highly potent sources of vitamin A can cause problems

PRESERVATION OF VITAMINS IN FOODS

• substantial amounts of vitamins can be lost from the time a fruit or vegetable is picked until it is eaten

• water-soluble vitamins can be destroyed with improper storage and excessive cooking

• heat, light, exposure to the air, cooking in water, and alkalinity are all factors that can destroy vitamins

• the sooner a food is eaten after harvest, the less chance of nutrient loss

• if the food is not eaten within a few days, freezing is the best preservation method to retain nutrients

• frozen vegetables and fruits are often as nutrient-rich as freshly picked ones

• fruits and vegetables are often frozen immediately after harvesting

Category: Biochemistry Notes