Vitamins and Micronutrients

Study Notes

Vitamins are organic compounds required in trace amounts (microgram to milligram quantities per day) in the diet for health, growth, and reproduction.
They cannot be synthesized in adequate quantities by humans.
Vitamins are classified as micronutrients because they are required in lesser amounts than macronutrients (carbohydrates, proteins, and lipids).

Vitamins are classified into two categories: water-soluble and fat-soluble.
Water-soluble vitamins: include folic acid, cobalamin, ascorbic acid, pyridoxine, thiamine, niacin, riboflavin, biotin, and pantothenic acid.
Fat-soluble vitamins: include vitamins A, D, K, and E.
Fat-soluble vitamins are released, absorbed, and transported with dietary fat, and are not readily excreted.

Water-soluble vitamins are readily excreted in the urine, and toxicity is rare.
Deficiencies can occur quickly.
Many water-soluble vitamins are precursors of coenzymes for the enzymes of intermediary metabolism.

Fat-soluble vitamins are stored in the liver and adipose tissue.
Consumption of vitamins A and D in excess of the Dietary Reference Intakes can lead to accumulation of toxic quantities of these compounds.
Only one fat-soluble vitamin (vitamin K) has a coenzyme function.

Vitamin A serves many important functions in the body, including its role in vision, reproduction, growth, and embryonic development, as well as immune function.
Dietary sources: animal-derived foods, such as liver, other organ meats, and fish oils, and plant sources like pumpkin, carrots, and most green vegetables.
Deficiency: may cause night blindness, very dry, rough skin, decreased resistance to infections, faulty tooth development, and slower bone growth.
Toxicity: nausea, vomiting, diarrhea, dizziness, drowsiness, and fatigue.

Vitamin D plays an essential role as a hormone in the control of calcium and phosphorous metabolism.
Vitamin D is also essential for dental health, preventing tooth decay and loss, strengthening the gums, and reducing the risk of oral infections.
Dietary sources: vegetables like mushrooms, fortified foods like breakfast cereals and oatmeal, and animal sources like egg yolk, cod liver oil, salmon, and tuna.
RDA: 600 IU (15 mcg) daily for adults 19 years and older, and 800 IU (20 mcg) daily for adults >70 years.
Deficiency: may cause rickets, osteomalacia, osteoporosis, alopecia areata, type 2 diabetes, and depression.