Scientists have discovered thirteen kinds of vitamins. They say vitamins help to carry out chemical changes within cells. If we do not get enough of the vitamins we need in our food, we are at risk of developing a number of diseases. Which foods should be eaten to keep us healthy? Let us look at some important vitamins. Vitamin A helps prevent skin and other tissues from becoming dry. People who do not get enough vitamin A cannot see well in darkness. Vitamin A is found in fish liver oil and the yellow part of eggs. Vitamin B-1 is also called thiamine. Thiamine changes starchy foods into energy. Thiamine is found not just in whole grains like brown rice, but also in beans and peas, nuts, and meat and fish. Vitamin B-12 is needed so folic acid can do its work. Together, they help produce red blood cells. Folic acid has been shown to prevent physical problems in babies when taken by their mothers during pregnancy. Vitamin B-12 is found naturally in foods like eggs, meat, fish and milk products. Vitamin B-12 is found in green leafy vegetables and other foods, like legumes and citrus fruits  . Vitamin C is needed for strong bones and teeth. The body stores little vitamin C. So we must get it every day in foods such as citrus fruits, tomatoes and uncooked cabbage. Vitamin D prevents the children's bone disease rickets  . Ultraviolet light from the sun changes a substance in the skin into vitamin D. Fish liver oil also contains vitamin D. Vitamin K is needed for healthy blood. It thickens the blood around a cut to stop bleeding. It can also be found in pork products, liver and in vegetables like cabbage, kale and spinach  . Vitamins are important to our health. A lack of required vitamins can lead to health problems. What is the main idea of the passage?
There are thirteen kinds of vitamins in total. One can not live without enough vitamins. Vitamins can carry out chemical changes within cells. Enough vitamins are vital to keep healthy.