Eugene Downey, age 14, of Pocatello, Idaho, for his question:

WHAT CAUSES RICKETS?

Rickets is a bone disease that mostly strikes children under 3 years of age. Often it is caused by a lack of calcium and vitamin D or by the body's inability to use these substances properly.

The bones are so soft that they bend into abnormal shapes. Rickets result in conditions called bowlegs, knock knees, chicken breast, funnel chest, rosary ribs and knobbed forehead. As the child grows, bones harden but the abnormal shape usually remains.

Doctors use X rays to diagnose rickets.

Eating foods rich in calcium and vitamin D usually prevents rickets. Calcium can be obtained by drinking plenty of milk and eating green vegetables. The best sources of vitamin D are sunlight and fish oils.