Scurvy is a disease that sailors commonly died from. It is caused by a lack of Vitamin C in your diet. Vitamin C is found in citrus fruits and some vegetables.
Ships had to carry enough food on long voyages to feed the crew. Without refrigeration, ships carried little fresh food, and sailors had very poor diets. The connection between scurvy and eating a healthful diet that included fruits and vegetables was not understood until late in the 18th century.