Chemical analysis of urine samples and tissues reveals that children who suffer night blindness are commonly deficient in several minerals but also have elevated sodium levels. Almost 14 million children worldwide have some degree of blindness because of a dietary deficiency of vitamin A, but the mineral profile of their tissues and urine samples reveals a marker that could be used to improve nutrition and help aid workers, particularly in the undeveloped world, reduce the risk of blindness.
via Nutritional deficiency and nightblindness.