The discovery of specific dietary insufficiencies as the cause of human disease played a central role in the development of modern nutritional science. In 1753, one of the first clinical trials showed that citrus fruit could prevent scurvy in sailors, leading to the identification of vitamin C as essential for health. By the mid-20th century, protective effects of many nutrients for deficiency diseases had been shown, including thiamine (beriberi), niacin (pellagra), vitamin D (rickets), vitamin A (night blindness), iron (anemia), and iodine (goiter).