The National Health and Nutrition Examination Survey (NHANES) is designed to assess the health and nutritional status of adults and children in the United States. The survey is unique in that it combines interviews with standardized physical examinations and laboratory tests. NHANES was conducted on a periodic basis from 1971 to 1994. In 1999 NHANES became continuous. Every year, approximately 5,000 people of all ages are interviewed in their homes and complete the health examination conducted in a mobile examination center. The NHANES interview includes demographic, socioeconomic, dietary, and health-related questions. The examination component consists of medical, dental, and physiological measurements, as well as the collection of biospecimens, such as blood and urine for laboratory testing.