An alarming number of young children in the US do not get enough vitamin D to avert health complications that are likely to stay silent until much later in the child’s adult life.  Calling it an invisible deficiency, researchers at Children’s Hospital Boston fear a future of easily broken bones and an impaired immune system may be in store for these children.

The researchers at Children’s Hospital, led by Catherine Gordon, examined 380 children between the ages of 8 months and 2 years and found that 40% of them had blood levels of vitamin D at levels considered less than optimum.  Gordon and her research team did not expect such a high rate of deficiency given the abundance of milk fortified with vitamin D in the US.

Vitamin D is made when the skin is exposed to sunlight but some foods, such as milk, are fortified with the vitamin for good measure.  Vitamin D plays an important role in keeping bones strong and healthy and it has also been linked to decreased risk  for cancer, kidney and arterial diseases.  Researchers in Canada recently reported poor prognosis for breast cancer patients who had low levels of vitamin D.  They were more likely to die or suffer metastasis than breast cancer patients with sufficient vitamin D levels.

There are no visible symptoms of vitamin D deficiency, which leads researchers to consider it a silent disease, but a blood test can determine blood levels of the vitamin.  Three children studied exhibited symptoms of weakened, soft bones associated with the disease rickets.  Thirteen more were found to show symptoms of bone demineralization, a condition caused when minerals vital to bone health leach out because of insufficient levels of vitamin D.

Vitamin D deficiency can sometimes be spotted by bowed legs in children or in children who suffer fractures easily.  They may also present with fatigue, and with severe deficiency, seizures.

Diabetes has been linked to vitamin D deficiency, too.  There is a tendency for overweight children, at risk for diabetes, to be deficient in vitamin D.

While sun exposure causes the body to manufacture vitamin D, it is thought that the smallest children may get limited exposure to the sun because adults are diligent about covering them up to avoid excessive exposure to the sun.

Even though the US supply of milk is almost always fortified with vitamin D, 6% of the children in the study who ate formula fortified with the vitamin were found to be deficient.  Breastfed children, too, are at risk of vitamin D deficiency as breast milk does not contain the vitamin.

The findings of the study have been published in the Archives of Pediatric and Adolescent Medicine.