Vitamin

A nutrient that the body needs in small amounts to function and stay healthy. Sources of vitamins are plant and animal food products and dietary supplements. Some vitamins are made in the human body from food products. Vitamins are either fat-soluble (can dissolve in fats and oils) or water-soluble (can dissolve in water). Excess fat-soluble vitamins are stored in the body’s  fatty tissue, but excess water-soluble vitamins are removed in the urine. Examples are vitamin A, vitamin C, and vitamin E.

Effect of cooking on vitamin content

Shown below is percentage loss of vitamins after cooking averaged for common foods such as vegetables, meat, fish.

Vitamin	C	B1	B2	B3	B5	B6	Folate	B12	A	E
Average %loss	16	26	-3	18	17	3	20	?	11	11

Table below shows effects of heat such as heat from boiling, steaming, cooking etc. and other agents on various vitamins. Effect of cutting vegetables can be seen from exposure to air and light. Water soluble vitamins such as B and C seep into the water when boiling a vegetable.

Vitamin	Soluble in Water	Exposure to Air	Exposure to Light	Exposure to Heat
Vitamin A	no	partially	partially	relatively stable
Vitamin C	very unstable	yes	yes	yes
Vitamin D	no	no	no	no
Vitamin E	no	yes	yes	no
Vitamin K	no	no	yes	no
Thiamine (B1)	highly	no	?	> 100°C
Riboflavin (B2)	slightly	no	in solution	no
Niacin (B3)	yes	no	no	no
Pantothenic Acid (B5)	quite stable	?	?	yes
Vitamin B6	yes	?	yes	?
Biotin (B7)	somewhat	?	?	no
Folic Acid B-9	yes	?	when dry	at high temp
Vitamin B-12	yes	?	yes	no

^{Source, Medical Dictionary, Wikepedia}