Vincent Legenza, age 13, of Helena, Mont., for his question:

WHY DO SOME PEOPLE GET RICKETS?

Rickets is a bone disease that happens mostly in children under 3 years of age. It may be caused by a lack of calcium and vitamin D or by the inability of the body to use these substances properly.

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

Some of the symptoms of rickets are sweating, especially on the head, weakness, flabbiness, pain in the bones and misshapen bones. Doctors use X rays to diagnose rickets.

Eating foods that are rich in calcium and vitamin D usually prevents rickets. You obtain calcium by drinking plenty of milk and eating green vegetables each day. Your best sources of vitamin D are sunlight and cod liver oil.

Fortunately rickets isn't too common in the United States and Canada today because the standard of living and nutrition have improved from olden days. In the past, many children had rickets because they did not eat well balanced diets adequate in vitamins and minerals.