Epidemiology
The estimated percentage of the population with a vitamin D deficiency varies based on the threshold used to define a deficiency. Recommendations for 25(OH)D serum levels vary across authorities, and probably vary based on factors like age; calculations for the epidemiology of vitamin D deficiency depend on the recommended level used.A 2011 Institute of Medicine (IOM) report set the sufficiency level at 20 ng/mL (50 nmol/L), while in the same year The Endocrine Society defined sufficient serum levels at 30 ng/mL and others have set the level as high as 60 ng/mL. As of 2011 most reference labs used the 30 ng/mL standard. : 435 Applying the IOM standard to NHANES data on serum levels, for the period from 1988 to 1994 22% of the US population was deficient, and 36% were deficient for the period  between 2001 and 2004; applying the Endocrine Society standard,  55% of the US population was deficient between 1988 and 1994, and 77% were deficient for the period between 2001 and 2004.In 2011 the Centers for Disease Control and Prevention applied the IOM standard to NHANES data on serum levels collected between 2001 and 2006, and determined that 32% of Americans were deficient during that period (8% at risk of deficiency, and 24% at risk of inadequacy). History
The role of diet in the development of rickets was determined by Edward Mellanby between 1918 and 1920. In 1921, Elmer McCollum identified an antirachitic substance found in certain fats that could prevent rickets.
Mediastinal shift is the deviation of the mediastinal structures towards one side of the chest cavity, usually seen on chest radiograph. It indicates a severe asymmetry of intrathoracic pressures. Mediastinal shift may be caused by volume expansion on one side of the thorax, volume loss on one side of the thorax, mediastinal masses and vertebral or chest wall abnormalities. An emergent condition classically presenting with mediastinal shift is tension pneumothorax. It is also a useful indicator of malignant pleural effusion.Mediastinal shift may be detected on antenatal ultrasound in certain fetal conditions. == References ==