328 Chapter 13 Nutrition Copyright Goodheart-Willcox Co., Inc. An excess of vitamin A from food is not common. However, an excessive intake of vitamin pills containing vitamin A can be dangerous. People who get too much vitamin A over a long period may experience fatigue, headaches, and vomiting. Vitamin D Vitamin D is often called the “sunshine vitamin.” This is because your body can manufacture vitamin D when your skin is exposed to sunlight. However, foods such as eggs and fortifi ed milk are more reliable sources. (Fortified means nutrients have been added to a food to improve its nutritional value.) Vitamin D that is not used is stored in the body. Excessive amounts of vitamin D may cause diarrhea, nausea, and headaches. Vitamin E The main function of vitamin E in the human body is to act as an antioxidant. This is a substance that protects compounds from the damaging effects of oxygen. Vitamin E protects blood cells and cells in the lungs from oxygen damage. It also protects vitamin A and fats in the body. Vitamin E is so widely distributed in foods that developing a defi ciency is rare. Because excess vitamin E is stored in the body, large doses from supplements may be harmful. Vitamin K A vitamin K defi ciency is rare because vitamin K is widely available in most diets. If a severe defi ciency occurs, however, it could cause bleeding. Although a vitamin K excess is also rare, it can be toxic. Bacteria in the human digestive tract make about half of the body’s needed vitamin K. The remaining need must be met by food sources. Water-Soluble Vitamins The B vitamins and vitamin C make up the second group of vitamins—the water-soluble vitamins. Excess amounts of water-soluble vitamins are excreted in the urine rather than stored in the body. Therefore, you need to eat good sources of these vitamins every day. Because these vitamins dissolve in water, it is best to cook most foods quickly in as little water as possible. After cooking, do not throw away cooking liquid. Instead, save it for use in a sauce or soup. Science Connection An Increasing Need for Vitamin D Recent research indicates that many children, teens, and adults are deficient in vitamin D. Extreme shortages of this vitamin may result in conditions called rickets in children and osteomalacia in older adults, both of which involve softening and weakening of the bones. The best way to find out if you are vitamin D deficient is to see your doctor. Treatment may include consuming dairy products and foods rich in vitamin D, taking supplements, and getting adequate sun exposure. (Note: Because sun exposure is linked to skin cancer, consult your doctor about the best way to make sure you get enough vitamin D.)