BOSTON -- It may not be enough to make your kids eats their vegetables every night. According to a new study out this month, more than 40 percent of children - from infants to teens - are vitamin D deficient. News Center 5's Liz Brunner reported Wednesday on the report.

Mike Stone and his brother Doug have always been healthy active boys. Their mom, Marla made sure they ate right, and drank their milk. But, at 14, after Stone complained of back pain, X-rays revealed a shocking discovery

VIDEO: Vitamin D Levels In Children Concerns Doctors

"He put it up to the light and you could essentially see right through the bones," said Stone.

Stone had a vitamin D deficiency. His bones were only 50 percent the density of a normal child his age. They could break at any moment. His younger brother, Doug, was also diagnosed with a vitamin D deficiency, but to a lesser degree.

"It's been estimated now that maybe 50 percent of children in US are at risk of vitamin D deficiency," said Dr. Michael Holick, of Boston University Medical Center.

Vitamin D is known as the "sunshine vitamin," and is produced by your skin in sunlight. It controls the amount of calcium absorbed from your diet and promotes materialization of teeth and bones.

"Vitamin D deficiency may increase risk for diabetes, arthritis, maybe cancers," Holick said.

Experts say the low levels of vitamin D in teens may be attributed to their lifestyle - more time spent on the computer than outside, and more kids using sun block. But according to a new study the problem may begin even earlier. Researchers at the Children's Hospital Boston found 12 percent of infants and toddlers were deficient in vitamin D, and 40 percent had below-optimal levels.

"Pediatricians believe human breast milk provides all nutrients infant requires, but it doesn't . They need vitamin D supplements," Holick said.

The good news is the problem can easily be reversed with supplements and treatment.