If you thought making your kids eat their veggies every night was enough to keep them healthy, this story may help change your mind.

According to a new study out this month, more than 40 percent of children, from infants to teens, are Vitamin D deficient.

You're about to meet one young man who found out the hard way.

Mike Stone and his brother Doug have always been healthy active boys.

Their mom Marla made sure they ate right, drank their milk and regularly saw their pediatrician.

Then at age 14, after Mike complained of back pain, x-rays revealed a shocking discovery.

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

Doctors told him that he was seriously Vitamin D deficient.

His bones were only 50 percent the density of a normal child his age and in risk of a fracture at any moment.

His younger brother Doug, who was just seven at the time, was also diagnosed as having Vitamin D deficiency, but to a lesser degree.

"It's been estimated now that maybe 50 percent of children in U.S. are at risk of Vitamin D deficiency," said Dr. Michael Holick, of the 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 mineralization of teeth and bones.

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

Experts say the low levels of Vitamin D in teens may be attributed to their lifestyle, more time spent on the computer than outside in the sunlight, plus an increase use of sunblock.

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," explained Dr. Holick.

"But it doesn't, they need Vitamin D supplementation."

The good news is the problem can easily be reversed.

This x-ray shows the arms of a child with severe Vitamin D deficiency.

And these after supplements and treatment.

Mike and his brother Doug now take supplements, eat more dairy products, and drink juice fortified with Vitamin D and their bone density has reached a normal level.

In addition to bone strength, Vitamin D is also beneficial is keeping teeth and gums healthy, especially in older adults.