David Wonderly, age 70, of Palmerton, Pa., for his question:

HOW MANY KINDS OF VITAMINS ARE THERE?

A vitamin is a complex substance that is essential to the human body for growth and health. All of the functions of the vitamins are not completely known, but we do know they seem to have specific uses that one cannot be replaced for another. Lack of one vitamin in an otherwise complete diet can result in a deficiency disease, such as rickets orscruvy.

At the present time scientists say we may soon be adding more vitamins to the list of about 25 we can currently identify.

There are two general classes: fat soluble vitamins which include A, D, E and K and the water soluble group which include C and the B complex vitamins.

Vitamin A was the first fat soluble vitamin discovered. It helps maintain skin, eyes, urinary tract and the linings of the nervous, respiratory and digestive systems. It is needed for the normal growth of bones and teeth. We obtain vitamin A in sweet potatoes, milk, liver, eggs, butter, green and yellow vegetables.

Vitamin B complex is about 15 water soluble vitamins which at first were believed to be only one. B 1, called thiamine (found in meat, whole grain cereals, nuts, soybeans, peas, potatoes and most vegetables) is needed to help the heart and nervous system function properly. B 2, called riboflavin (found in milk, cheese, liver, fish and poultry) is needed to help body cells use oxygen, to promote tissue repair and to maintain healthy skin.

Vitamin C, called ascorbic acid, is essential for sound bones and teeth and is also needed for tissue metabolism and wound healing. It can be found in citrus fruits, tomatoes, raw cabbage, potatoes, strawberries and cantaloupe.

Vitamin D is a group of about 10 fat soluble vitamins that are essential for calcium and phosphorus metabolism. Use of the vitamin also prevents rickets. We obtain it in fish liver oils, fortified milk, eggs, tuna, salmon and sunlight.

Vitamin E (found in whole grain cereals, lettuce and vegetable oils) helps maintain heart and skeletal muscles while vitamin K (found in leafy vegetables and made by intestinal bacteria) is needed for normal blood clotting.

One of the earliest men in history to realize the harm of vitamin deficiency was Kanehiro Takaki, surgeon general of the Japanese Navy, who in 1882 was able to greatly reduce the number of beriberi cases on ships crews by adding meat and vegetables to their rice diets.