Vitamins are essential organic compounds required in minute quantities for proper growth and nutrition. As vitamins cannot be synthesized by the human body and must be supplied through the diet.
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Fat soluble vitamins
Fat soluble vitamins are soluble in lipids. They have common isoprene structure; 5 carbon unsaturated branched compounds. Although they have common structure, they do not have common function. Due to their lipid solubility property, they are not excreted by kidneys. They are absorbed from intestine and absorption depends on bile emulsification, pancreatic secretion, condition of ileum.
Deficiency can occur by malabsorption syndrome, steatorrhea, mineral oil intake, conditions like cystic fibrosis, celiac disease, post ileectomy condition etc.
They accumulate in fat and can be stored. Toxicity is more common than that of water soluble vitamins.
Fat soluble vitamins are
- Vitamin A
- Vitamin D
- Vitamin E
- Vitamin K
Water soluble vitamins
Water soluble vitamins are not soluble in fat. These do not have common structure but have common function. Most of the water soluble vitamins have co-enzyme role or precursor to co-enzyme role in metabolism (Vitamin K is fat soluble but have co-enzyme function). Due to their lipid insolubility, they easily get excreted by kidneys except Vitamin B9, B12.
Water soluble vitamins are
- Vitamin B1 (Thiamine, Thiamine Pyrophosphate)
- Vitamin B2 (Riboflavin, FAD, FMN)
- Vitamin B3 (Niacin, NAD)
- Vitamin B5 (Pantothenic acid, CoA)
- Vitamin B6 (Pyridoxine, Pyridoxal 5´-phosphate)
- Vitamin B7 (Biotin)
- Vitamin B9 (folate)
- Vitamin B12 (cobalamine)
- Vitamin C (Ascorbic acid)
- Menadione (Vitamin K3 , water soluble form of vitamin K)
Atypical vitamins
Atypical vitamins are those vitamins which can be synthesized on body by human enzymes.
- Vitamin D: from cholesterol.
- Vitamin B3 (Niacin, NAD): from tryptophan.
Dietary supplementation of vitamins in special dietary conditions:
| Supplementation required: | Diet |
| Vitamin B2, B12, Vitamin D | Vegetarian/ vegan diet. Vitamin B12 and Vitamin D have no plant source. |
| Vitamin B7 | Raw egg white. Avidin present in eggs white interferes with vitamin B7 absorption. |
| Vitamin B3 | When majority of diet is corn. |
References:
- Harper’s Illustrated Biochemistry Thirty Second Edition.
- Lippincott’s Illustrated Reviews – Biochemistry.
