When the body doesn't get the nutrients it needs, its health may suffer. The lack of essential nutrients in the system is called a nutritional deficiency. As the pellagra video demonstrates, a vitamin deficiency, such as too little niacin, can lead to serious disease. Vitamins are organic substances found in minute amounts in many foods. They are essential to the body's normal metabolic functioning.

A vitamin deficiency occurs when the body is deprived of a particular vitamin for a period of time. If the deficiency persists, disease can set in. People at risk of developing a vitamin deficiency include those who rarely eat fruits and vegetables, those who are under high amounts of stress, those experiencing or recovering from illness that causes decreased appetites, those dieting to lose weight, and pregnant or nursing women. Today, most vitamin deficiencies can be detected through a simple blood test.

Vitamin deficiency diseases act on the body in different ways. For example, scurvy, one of the oldest recorded vitamin deficiency diseases, is caused by a lack of vitamin C. It famously afflicted sailors exploring the New World, and its symptoms include fatigue; irritability; depression; and bleeding from the gums, under the skin, and around bones and vital organs. The body needs vitamin C to form healthy connective tissue and gums, strengthen blood vessels, and produce red blood cells. Good sources of vitamin C are citrus fruits, strawberries, cantaloupe, and broccoli.

Other vitamin deficiency diseases besides scurvy and pellagra include rickets, a bone disease caused by too little vitamin D; night blindness, or difficulty seeing in dim light, which is caused by a lack of vitamin A; and pernicious anemia, a condition in which the body does not make enough red blood cells because of a lack of vitamin B₁₂. Since vitamin B₁₂ is not produced by the body and is only found in animal sources, including beef, pork, seafood, and cheeses, those who refrain from eating meats and milk products need to take B₁₂ supplements.

The best way to avoid vitamin deficiency is to eat a variety of foods that include fruits, vegetables, lean meats, complex carbohydrates, and healthy fats. Avoiding alcohol and not smoking can help by decreasing the risk of nutrient depletion. Taking supplements can make up for vitamins that a diet might lack. However, because a vitamin overdose can lead to dangerous medical conditions, only physicians or licensed nutritionists should determine appropriate supplement levels.

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