Chapter 10: Micronutrients Overview and Role as Antioxidants

10.1 Vitamins

The name vitamin comes from Casimir Funk, who in 1912 thought vital amines (NH3) were responsible for preventing what we know now are vitamin deficiencies. He coined the term ‘vitamines’ to describe these compounds. Eventually it was discovered that these compounds were not amines and the ‘e’ was dropped to form vitamins.[1]

Vitamins are organic compounds that are traditionally assigned to two groups fat-soluble (hydrophobic) or water-soluble (hydrophilic). This classification determines where they act in the body. Water-soluble vitamins act in the cytosol of cells or in extracellular fluids such as blood; fat-soluble vitamins are largely responsible for protecting cell membranes from free radical damage. The body can synthesize some vitamins, but others must be obtained from the diet. The table below shows the two categories of vitamins, and also shows both the common names and numbers of the B vitamins.  Most B vitamins are known by their common names, except for vitamin B6 and vitamin B12.

Table 10.11 Fat-soluble and water-soluble vitamins

Fat-Soluble Vitamins Water-Soluble Vitamins
  • Vitamin A
  • Vitamin D
  • Vitamin E
  • Vitamin K
  • Vitamin C
  • All B Vitamins:
    • Thiamin (B1)
    • Riboflavin (B2)
    • Niacin (B3)
    • Pantothenic acid (B5)
    • Pyridoxine (B6)*
    • Biotin (B7)
    • Folate (B9)
    • Cobalamin (B12)*
* Vitamins B6 and B12 are known by their numbers

Before they even knew that vitamins existed, a scientist named E.V. McCollum recognized that a deficiency in what he called ‘fat-soluble factor A’ resulted in severe ophthalmia (inflammation of the eye). In addition, a deficiency in ‘water-soluble factor B’ resulted in beriberi (a deficiency discussed more later).

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Figure 10.11 Factor A deficiency led to ophthalmia, factor B deficiency led to beriberi

Factor A is what we now know as vitamin A. However, researchers soon realized that factor B actually consisted of two factors that they termed B1 and B2. Then they realized that there are multiple components in B2, and they began identifying the wide array of B vitamins that we know today.[2]

You might be thinking “but the numbers on the B vitamins still do not add up.” You are right, vitamins B4, B8, B10, and B11 were discovered and then removed leaving us with the B vitamins shown in Table 10.11.

Relative to other scientific milestones, the discovery of vitamins is a fairly recent occurrence, as shown in Table 10.12.

Table 10.12 Vitamin, year proposed, isolated, structure determined, and synthesis achieved up to 1944[3]

Vitamin

Year Proposed

Isolated

Structure Determined

Synthesis Achieved

Thiamin

1901

1926

1936

1936

Vitamin C

1907

1926

1932

1933

Vitamin A

1915

1939

1942

–

Vitamin D

1919

1931

1932

1932

Vitamin E

1922

1936

1938

1938

Niacin

1926

1937

1937

1867*

Biotin

1926

1939

1942

1943

Vitamin K

1929

1939

1942

1943

Pantothenic Acid

1931

1939

1939

1940

Folate

1931

1939

–

–

Riboflavin

1933

1933

1934

1935

Vitamin B6

1934

1936

1938

1939

* Was established long before it was known to be a vitamin

Vitamin Absorption[4]

One major difference between fat-soluble vitamins and water-soluble vitamins is the way they are absorbed in the body. Vitamins are absorbed primarily in the small intestine and their bioavailability is dependent on the food composition of the diet. Fat-soluble vitamins are absorbed along with dietary fat. Therefore, if a meal is very low in fat, the absorption of the fat-soluble vitamins will be impaired. Once fat-soluble vitamins have been absorbed in the small intestine, they are packaged and incorporated into chylomicrons along with other fatty acids and transported in the lymphatic system to the liver. Water-soluble vitamins on the other hand are absorbed in the small intestine but are transported to the liver through blood vessels.  (Figure 10.12 “Absorption of Fat-Soluble and Water-Soluble Vitamins”).

Process of vitamin absorption in body
Figure 10.12 Absorption of Fat-Soluble and Water-Soluble Vitamins

The following two tables give an overall summary of the vitamins.  You’ll be learning more about each in detail over the next few chapters.

Table 10.13 Fat-Soluble Vitamins

Vitamin Sources Recommended Intake for adults Major functions Deficiency diseases and symptoms Groups at risk of deficiency Toxicity UL
Vitamin A (retinol, retinal, retinoic acid,carotene, beta-carotene) Retinol: beef and chicken liver, skim milk, whole milk, cheddar cheese; Carotenoids: pumpkin, carrots, squash, collards, peas 700-900 mcg/day Antioxidant,vision, cell differentiation, reproduction, immune function Xerophthalmia, night blindness, eye infections; poor growth, dry skin, impaired immune function People living in poverty (especially infants and children), premature infants, pregnant and lactating women people who consume low-fat or low-protein diets Hypervitaminosis A: Dry, itchy skin, hair loss, liver damage, joint pain, fractures, birth defects, swelling of the brain 3000 mcg/day
Vitamin D Swordfish, salmon, tuna, orange juice (fortified), milk (fortified), sardines, egg, synthesis from sunlight 600-800 IU/day (15-20 mcg/day) Absorption and regulation of calcium and phosphorus, maintenance of bone Rickets in children: abnormal growth, misshapen bones, bowed legs, soft bones; osteomalacia in adults Breastfed infants, older adults people with limited sun exposure, people with dark skin Calcium deposits in soft tissues, damage to the heart, blood vessels, and kidneys 4000 IU/day (100 mcg/day)
Vitamin E Sunflower seeds, almonds, hazelnuts,peanuts 15 mg/day Antioxidant, protects cell membranes Broken red blood cells, nerve damage People with poor fat absorption, premature infants Inhibition of vitamin K clotting factors 1000 mcg/day from supplemental sources
Vitamin K Vegetable oils, leafy greens, synthesis by intestinal bacteria 90-120 mcg/day Synthesis of blood clotting proteins and proteins needed for bone health and cell growth Hemorrhage Newborns, people on long term antibiotics Anemia, brain damage ND

Table 10.14 Water-Soluble Vitamins

Vitamin Sources Recommended Intake for adults Major Functions Deficiency diseases and symptoms Groups at risk of deficiency Toxicity UL
Vitamin C (ascorbic acid) Orange juice, grapefruit juice, strawberries, tomato, sweet red pepper 75-90 mg/day Antioxidant, collagen synthesis, hormone and neurotransmitter synthesis Scurvy, bleeding gums, joint pain, poor wound healing, Smokers, alcoholics, elderly Kidney stones, GI distress, diarrhea 2000 mg/day
Thiamin (B1) Pork, enriched and whole grains, fish, legumes 1.1-1.2 mg/day Coenzyme: assists in glucose metabolism, RNA, DNA, and ATP synthesis Beriberi: fatigue, confusion, movement impairment, swelling, heart failure Alcoholics, older adults, eating disorders None reported ND
Riboflavin (B2) Beef liver, enriched breakfast cereals, yogurt, steak, mushrooms, almonds, eggs 1.1-1.3 mg/day Coenzyme: assists in glucose, fat and carbohydrate metabolism, electron carrier, other B vitamins are dependent on Ariboflavinosis: dry scaly skin, mouth inflammation and sores, sore throat, itchy eyes, light sensitivity None None reported ND
Niacin (B3) Meat, poultry,  fish, peanuts, enriched grains 14-16 NE/day Coenzyme: assists in glucose, fat, and protein metabolism, electron carrier Pellagra: diarrhea, dermatitis, dementia, death Alcoholics Nausea, rash, tingling extremities 35 mg/day from fortified foods and supplements
Pantothenic Acid (B5) Sunflower seeds, fish, dairy products, widespread in foods 5 mg/day Coenzyme: assists in glucose, fat, and protein metabolism, cholesterol and neurotransmitter synthesis Muscle numbness and pain, fatigue, irritability Alcoholics Fatigue, rash ND
B6(Pyridoxine) Meat, poultry, fish, legumes, nuts 1.3-1.7 mg/day Coenzyme; assists in amino-acid synthesis, glycogenolysis, neurotransmitter and hemoglobin synthesis Muscle weakness, dermatitis, mouth sores, fatigue, confusion Alcoholics Nerve damage 100 mg/day
Biotin Egg yolks, fish, pork, nuts and seeds 30 mcg/day Coenzyme; assists in glucose, fat, and protein metabolism, amino-acid synthesis Muscle weakness, dermatitis, fatigue, hair loss Those consuming raw egg whites None reported ND
Folate Leafy green vegetables, enriched grains, orange juice 400 mcg/day Coenzyme; amino acid synthesis, RNA, DNA, and red blood cell synthesis Diarrhea, mouth sores, confusion, anemia, neural-tube defects Pregnant women, alcoholics Masks B12 deficiency 1000 mcg/day from fortified foods and supplements
B12(cobalamin) Meats, poultry, fish 2.4 mcg/day Coenzyme; fat and protein catabolism, folate function, red-blood-cell synthesis Muscle weakness, sore tongue, anemia, nerve damage, neural-tube defects Vegans, elderly None reported ND
Choline Egg yolk, wheat, meat, fish, synthesis in the body 425-550 mg/day Synthesis of neurotransmitters and cell membranes, lipid transport Non-alcoholic fatty liver disease, muscle damage, interfered brain development in fetus None Liver damage, excessive sweating, hypotension 3500 mg/day
  1. Carpenter K. (2003) A short history of nutritional science: Part 3 (1912-1944). J Nutr 133(10):3023-3032. https://academic.oup.com/jn/article/133/10/3023/4687555 ↵
  2. Carpenter K. (2003) A short history of nutritional science: Part 3 (1912-1944). J Nutr 133(10):3023-3032 ↵
  3. Carpenter (2003) ↵
  4. Fialkowski-Revilla, et al. Human Nutrition ↵
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