Rickets is a deficiency disease caused by a lack of minerals in the bones. In the 1800s the disease was widespread in the poor districts of industrial cities in Great Britain and the United States.
Minerals are used to strengthen bones - without them bones become soft and bent. The symptoms of rickets usually started showing in young children who grew up with twisted and bent limbs. The body needs vitamins and sunlight to be able to absorb minerals into the skeleton. Therefore, rickets was particularly common among the poor, whose diet did not provide enough vitamins, and among people who did not get a lot of sunlight.
In the early 1900s researchers discovered the role of vitamins and sunlight in the development of bones. Measures such as enriching milk with vitamin D, and the regular intake of cod-liver oil or frequent exposure to sunlight, helped prevent further outbreaks.