Vitamin D promotes the body's absorption of calcium, which is essential for the normal development and maintenance of healthy teeth and bones. Calcium is also important to nerve cells, including the brain.

Vitamin D also helps maintain adequate blood levels of calcium and phosphorus.

Vitamin D is found in the following foods:

• Dairy products
  • Cheese
  • Butter and margarine
  • Cream
  • Fortified milk (all milk in the United States is fortified with vitamin D)
• Fish
• Oysters
• Fortified cereals

A vitamin D deficiency can lead to osteoporosis in adults or rickets in children.

Excessive doses of vitamin D can result in increased calcium absorption from the intestinal tract. This may cause increased calcium resorption from the bones, leading to elevated levels of calcium in the blood. Elevated blood calcium may then cause calcium deposition in soft tissues such as the heart and lungs. This can reduce their ability to function.

Kidney stones, vomiting, and muscle weakness may also occur due to the ingestion of too much vitamin D.

Recommended daily allowances (RDAs) are defined as the levels of intake of essential nutrients that, on the basis of scientific knowledge, the Food and Nutrition Board judges to be adequate to meet the known nutrient needs of practically all healthy persons.

The best way to get the daily requirement of essential vitamins is to eat a balanced diet that contains a variety of foods from the food guide pyramid.

Vitamin D is also known as the "sunshine vitamin" because the body manufactures the vitamin after being exposed to sunshine. Ten to 15 minutes of sunshine 3 times weekly is adequate to produce the body's requirement of vitamin D.

Specific recommendations for each vitamin depend on age, gender, and other factors (such as pregnancy). The U.S. Department of Agriculture has a PDF file that lists these recommendations.