water-Soluble Vitamins

We have so far studied the fat-soluble vitamins. Let  us now move on to the water-soluble  ones. Vitamin C and  vitamins  of the B-complex group are known as water-soluble vitamins owing to their solubility in water. Unlike the fat-soluble vitamins,  these vitamins cannot be stored in our body  in  considerable amounts. The excess amount of these vitamins is instead  excreted from the body in the urine. 

Vitamins of the  B-Complex Group 

As the name indicates, this  is a group of vitamins with  similar  functions. Vitamins of the B-Complex group include: thiamine(B1),  riboflavin (B2), folic acid, niacin and vitamin B12 They usually occur together in foods. The B vitamins act as coenzymes and help in the metabolism of carbohydrates, proteins and fats. You are already  familiar with enzymes. What  are coenzymes? Coenzymes are substances which are needed by enzymes to do their job  effectively. Hence they can be considered as the helpers of specific  enzymes. In fact these  enzymes cannot function in the absence of their specific coenzymes.

Enzymes  and coenzymes act together 

Let us now learn more about the food  sources, absorption, storage and functions of each of these  vitamins.

Thiamine or B1: Thiamine or B1 is  widely distributed in animal and plant foods. Almost  all  the  foodstuffs  except fats, oils and  sugar contain small amounts of  thiamine.  Plant  foods such as whole grain cereals (i.e. wheat and rice) and whole pulses are also rich sources of thiamine. 

Among  the foods of animal origin lean meats,  poultry  and egg yolk are good sources. One point that needs to  be emphasized  here is  that the processing of cereals  and pulses can  significantly alter  their  thiamine content as well as the content of some of the  other  vitamins. You  will find more information on this aspect in  Highlight.  The discussion is  relevant not  just to thiamine but to other vitamins as well. 

• Processing of wheat: Wheat is usually not consumed in the  form of wheat grains as such  but in the processed form e.g. whole wheat flour (atta), refined wheat flour (maida and suji/rawa). Most of the thiamine and  other B vitamins are present in  the outer covering  or bran and the germ layer of the wheat grain. Atta or whole  wheat flour has most of the  bran and part of the germ  layer in  it and is a good source of thiamine. However, maida and suji have very  little bran and germ and hence are poor sources of thiamine and other B-complex vitamins in general. 
• Processing of rice: Polished rice is very poor in  B-complex vitamins thiamine in particular. What do we mean by polishing? Paddy (or rice with husk) is either ground in machines or pounded by hands to remove the outer husk. After this the grain is further cleaned to give it a  white, polished appearance. Removal of husk and polishing both cause heavy losses of thiamine as well as some of the other B vitamins Rice is also  available in another form called parboiled (sela) rice.  Parboiled rice is prepared by soaking raw rice in water for 2 to 3 days. boiling or steaming and then drying. During this process most of the  nutrients present in the outer layers of the  grain move to its interior. Thus thiamine and the other vitamins are  not lost when the outer layers of rice are removed during subsequent processing. 
• Sprouting  and  fermentation: Sprouting and fermentation of whole  grain cereals or pulses  increases their content of B-complex vitamins and vitamin C. Sprouting, as you  know, is the process of growing or germination of seeds or grains by  first soaking them in water and  then leaving the grains moist for about 24 hours by wrapping them in moist cloth. You can sprout whole pulses like green gram and use them for making raita  (a curd preparation), stuffed paranthas or eat  them as such in  the form of salads.

  

  Sprouting of grains

Fermentation, on the other  hand, refers to the chemical changes taking place in certain foods when mixed  in a ground form with added fluid and kept overnight at a  suitable temperature. During this time certain beneficial bacteria multiply and grow in the fad mixture and bring about some desirable  changes in  it.  You may already be familiar with these  changes. 

Fermentation  makes the mixture light and fluffy in appearance and more digestible.  Let  us now  talk about some fermented foods. Idlis are commonly consumed in the  south and are made by steaming a  fermented mixture of rice and urad dal. Similarly dhokla, a dish consumed in West India (Gujarat), is prepared by steaming  a  fermented mixture of curd  and besan  (bengal gram flour). 

After  ingestion, thiamine is absorbed and enters the  bloodstream.  It is utilized to perform several important functions. Excess thiamine (i.e. the amount in excess of the  body  needs) is excreted in the  urine. 

You would  now be interested in finding  out  what  exactly thiamine does in  the body. Thiamine plays an important role in the metabolism of carbohydrates. We mentioned  coenzymes before. Thiamine forms a part of a specific coenzyme involved  mainly  in carbohydrate metabolism. The main function of this  coenzyme is its role in the  burning or oxidation of glucose to produce  energy. 

Riboflavin or B2: Riboflavin or B2 is widely distributed in plant and animal foods. Milk, liver, kidney, eggs and green leafy vegetables are good sources of riboflavin. Whole grain cereals and pulses contain fair amounts. On refining there is some loss of the vitamin.  However, sprouting and fermentation of whole grain cereals and pulses can markedly increase their content of riboflavin and other B vitamins as mentioned in Highlight. An average mixed diet including milk, green leafy vegetables, whole cereals and pulses (especially when sprouted) can take care of the riboflavin needs  of vegetarians. Non-vegetarians can also obtain riboflavin from animal foods. 

The riboflavin which we ingest  is absorbed from the upper part of the  small intestine into  the bloodstream and is taken to various body  tissues to perform specific functions. Like other water-soluble vitamins, excess riboflavin is  excreted in the urine. 

How is  riboflavin used by the body? Riboflavin plays an important role in  the metabolism of carbohydrates, fats  and proteins. This is because of the  fact  that it forms part of  two  distinct coenzymes  which help to release energy from the end products of digestion of carbohydrates,  fats and proteins. 

Niacin: Niacin is another member of the B-complex  family. The good sources of niacin  include meat, fish, poultry, cereals, pulses, nuts and oilseeds. One interesting  point about niacin is  that it can also be formed in  the  body from an amino acid called tryptophan. Milk is a good example of a food rich in tryptophan but not in  niacin. The tryptophan present in milk protein can be converted to niacin  in the  body. Thus milk provides appreciable amounts of niacin. 

Niacin  (like riboflavin) is also part of coenzymes which help to release energy from  the end products of the digestion of carbohydrates, fats  and proteins. It thus helps in their metabolism. 

Folic acid: Folic acid is also widely-distributed in foods. Green leafy vegetables and organ meats (like liver ,and kidney) are very  rich sources of folic acid. Whole grain cereals, pulses,  eggs and dairy products are also good sources of folic acid. 

After absorption folic acid is taken to various  body tissues through the bloodstream  for specific functions. Normally  some amount of folic acid is stored in  the body. The principal storage organ is the liver. Under  normal circumstances, the body stores of folic acid are sufficient to meet the requirements  of the body for several months even if  no folic acid  is available through the diet. Folic acid  plays an important role in blood formation. You may be aware that blood has three kinds of cells red blood cells, white blood cells and platelets  suspended in a  fluid called plasma. Folic acid is important for the proper development of  red blood cells. 

Vitamin B12 or Cobalamin: Vitamin BI2 or cobalamin is present only in the foods of animal origin. Liver, kidney, milk, eggs and sea foods (e.g. shrimps, crabs, lobsters) are rich sources of vitamin BI2. Plant  foods do not contain the  vitamin. Vitamin B12 is also synthesized  in our body in the intestinal tract by certain helpful bacteria. 

Vitamin B12 can only be absorbed in the presence of a specific chemical substance called intrinsic factor. This substance is secreted by the cell of the stomach. Vitamin B12 ingested combines with  intrinsic factor and is absorbed  from the small  intestine. Bacteria  present in the intestine can  also  produce vitamin B12. But this cannot be absorbed  without the intrinsic factor which is found only in the stomach. The vitamin B12 produced by the bacteria is hence excreted from the body through faeces. 

Our body's requirement for vitamin B12 is very  small. Consumption of even small amounts of animal foods like milk can take care of the vitamin B12 needs  of the body. 

Vitamin B12 is necessary for the proper functioning  of  the digestive  tract, nervous system  and the bone marrow. In the bone  marrow, vitamin B12 (like folic acid) is also involved in the formation  of normal red blood cells.

Vitamin C 

Vitamin  C or ascorbic acid  is also termed as the "fresh food vitamin" because fresh fruits and vegetables are its major sources. Fresh  citrus fruits (like orange, lime and lemon) and other  fruits  and vegetables  like guava, amla, papaya, green  leafy vegetables, tomatoes, green  chillies and capsicum are some of the excellent sources of vitamin C. Root vegetables  like potato and sweet potato contain small amounts of  the vitamin and they contribute significant amounts only when consumed in  large quantities.  Cereals and pulses as such are poor  in vitamin  C  but  when sprouted and fermented become good  sources.  Animal foods like fish, meat, milk, poultry and eggs contain little or no ascorbic acid. 

Vitamin C is a fresh food vitamin

Fruits like amla, guava,  green leafy  vegetables and green chillies are examples of some of the  cheap sources of vitamin C. In fact, amla is the cheapest source and provides 20 times or more  ascorbic acid as compared to the expensive citrus fruits. 

Ascorbic acid  is  readily absorbed  from the digestive tract  and is  then  distributed to various  body tissues. Organs and glands like the spleen, bone marrow, liver, pancreas,  kidney and the retina of the eye  have a high concentration of ascorbic acid. 

Functions: Do you know that vitamin C 

• plays a role in healing of wounds 
• aids in the absorption of iron (a mineral which  plays a role in blood formation) 
• helps to overcome conditions of injury, infection and other stresses and 
• prevents destruction of certain substances present in the body as well as in some foodstuffs. 

These are some of the interesting facts about the functions of vitamin C. Wouldn't you like to know more about them? Let us now take each of the above mentioned functions  and study them in some detail. Vitamin C plays a  role in:

1. Wound healing: Vitamin C plays an important role in the formation of a special kind of protein called collagen. The formation of collagen at the site of wound or injury aids in its healing. This protein is found in the connective tissue which holds together different other tissues much like cement holds bricks together. Forexample, collagen present in blood vessels makes them firm. Deficiency of vitamin C in the diet may result in fragile blood vessels which can easily rupture. 
2. Dealing with stress: Ascorbic acid  plays an important role in the release of two hormones epinephrine and norepinephrine from the adrenal glands of the body. These hormones help the  body to deal with stressful situations like day-to-day tensions, stresses of infections and injury. 
3. Absorption of iron: Iron is an essential component of  red blood cells. Vitamin C aids absorption of iron by converting it into a more suitable form for absorption. 
4. Protecting certain substances from destruction: Like vitamin E, vitamin C protects certain substances e.g. vitamin A and unsaturated fatty acids from being destroyed.