At least 40 percent of American infants and toddlers are not getting enough vitamin D, according to a recent report in Archives of Pediatrics and Adolescent Medicine.

Twelve percent of the youngest children across the nation are already deficient in vitamin D, and another 28 percent are at risk for vitamin D deficiency, according to the study.

Because human breast milk frequently lacks sufficient vitamin D, the number of babies in the research sample being breastfed was important to the findings.

Vidamin D, also known as the sunshine vitamin, is produced naturally when the body reacts to sunlight. Recent recommendations by the American Academy of Pediatriacs (AAP) and American Cancer Society have urged people to limit exposure to ultraviolet light by minimizing sunlight exposure and using sunscreen.

"These data underscore the fact that breastfed infants should be supplemented with vitamin D," says study author Dr. Catherine Gordon at Children's Hospital in Boston. She adds that mothers who are breastfeeding often need vitamin D supplements as well.

According to the AAP, infants who are breastfed but do not receive supplemental Vitamin D or adequate sunlight exposure are at increased risk of developing Vitamin D deficiency.

University Medical Center at Brackenridge Neonatal Dietition Candice Ware, RD, LD, says: "Many parents of infants and toddlers are much more cautious with sunlight exposure than in previous decades. Breastfeeding will always be the gold standard for infant nutrition. However, some breastfed infants are at risk for developing Vitamin D deficiency, especially if they live in areas of the country with low amounts of sunlight, if they have dark pigmented skin, or if the mother of the breastfed infant is deficient herself."

"Giving a multivitamin recommended by the child's pediatrician to breastfed infants is a simple solution to preventing Vitamin D deficiency while keeping the child safe from harmful UV rays and continuing to provide the limitless benefits of breast milk."

Low Levels a Risk for Disease

Other factors that may contribute to low levels of Vitamin D include not drinking enough Vitamin D-fortified milk (for toddlers). Few foods naturally contain vitamin D, which is essential for strong bones because it helps the body absorb calcium.

In addition to helping maintain bone health, Dr. Gordon says that Vitamin D also appears to play a role in maintaining the immune system.

Persons with low levels of vitamin D may be more susceptible to autoimmune diseases, such as type 1 diabetes and multiple sclerosis, and to certain cancers.

The current study included 380 children between eight and 24 months old. About 80 percent were from urban areas, and the majority of the youngsters were African American or Hispanic, according to the study.

For this study, the researchers defined severe vitamin D deficiency as blood levels of less than 8 nanograms per milliliter (ng/mL), vitamin D deficiency as less than 20 ng/mL and suboptimal as less than 30 ng/mL. Critics believe the determination of deficiency was set too high.

Dr. Gordon says there is some debate within the medical community about what truly signifies vitamin D deficiency, but that they felt current evidence supports the levels they used, and less than 20 ng/mL is the level her hospital uses as a cut-off point.

See Your Baby's Doctor

If you are concerned that your baby may have low levels of Vitamin D or whether to supplement, consult your baby's doctor. Your physician can recommend the proper type and amount of vitamin D supplement for your baby. The American Academy of Pediatrics recommends that babies who are exclusively breastfed receive additional vitamin D beginninig at two months of age.