Thin Bones Seen In Boys With Autism And Autism Spectrum Disorder

The researchers believe that boys with autism and ASD are at risk for poor bone development for a number of reasons. These factors are lack of exercise, a reluctance to eat a varied diet, lack of vitamin D, digestive problems, and diets that exclude casein, a protein found in milk and milk products. Dairy products provide a significant source of calcium and vitamin D. Casein-free diets are a controversial treatment thought by some to lessen the symptoms of autism.

Funding for the study was provided by the NIH’s National Institute of Child Health and Human Development and National Center for Research Resources. The research team that conducted the study was led by Mary L. Hediger, Ph.D., a biological anthropologist in NICHD’s Division of Epidemiology, Statistics and Prevention Research.

“Our results suggest that children with autism and autism spectrum disorder may be at risk for calcium and vitamin D deficiencies,” Dr. Hediger said. “Parents of these children may wish to include a dietitian in their children’s health care team, to ensure that they receive a balanced diet.”

Dr. Hediger stressed that the current study results need to be confirmed by larger studies. Until definitive information is available, however, it would be prudent for parents of children with autism and ASD to include a dietitian in their care, particularly if the children’s diets do not include dairy products or they are not otherwise eating a balanced diet, she said. Because girls are much less likely to have autism or ASD than are boys, the researchers were unable to enroll a sufficient number of girls within the short time frame of the study to allow them to draw firm conclusions. Dr. Hediger added that if a girl with autism or ASD is not eating dairy products or eating a balanced diet, it would be prudent for a dietitian to be included in her health care team.

Autism is a complex brain disorder involving communication and social difficulties as well as repetitive behavior or narrow interests. Autism is often grouped with similar disorders, which are often referred to collectively as autism spectrum disorders. The underlying causes of autism and ASD are unclear. There is no cure for the disorders and treatments are limited.

When the boys were enrolled in the study, the researchers asked the boys’ parents if the boys were taking over-the-counter or prescription medications, were taking any vitamin or mineral supplements, or were on a restricted diet.

During the study, researchers X-rayed the hands of 75 boys between the ages of 4 and 8 years old who had been diagnosed with autism or ASD. The researchers then measured the thickness of the bone located between the knuckle of the index finger and the wrist and compared its development to a standardized reference based on a group of boys without autism.

Dr. Hediger said that the research team measured cortical bone thickness. She added that this procedure was done as a substitute for a conventional bone scan, which measures bone density. Bone density is an indication of bones’ mineral content. Less dense bones may indicate a risk of bone fracture.

The researchers used the measure of bone thickness because many of the boys were unable to remain still long enough for the conventional scan, which requires individuals to lie immobile for an extended period of time. To successfully complete the bone scan, many of the boys would have required sedation—a step the researchers were reluctant to take for an early study.

The hand X-ray, Dr. Hediger explained, offers an approximate indication of bone density. She added, however, that because the researchers were unable to use a conventional bone scan, the results of the current study should be confirmed by additional studies using conventional bone scans.

The investigators found that the bones of the boys with autism were growing longer but were not thickening at a normal rate. During normal bone development, material from inside the bone is transferred to the outside of the bone, increasing thickness, while at the same time, the bones are also growing longer.

At 5 or 6 years of age, the bones of the autistic boys were significantly thinner than the bones of boys without autism and the difference in bone thickness became even greater at ages 7 and 8.

The bone thinning was particularly notable because the boys with autism and ASD were heavier than average and would therefore be expected to have thicker bones.

The researchers do not know for certain why the boys had thinner than normal bones. A possible explanation is lack of calcium and vitamin D in their diets. Dr. Hediger explained that a deficiency of these important nutrients in the boys’ diets could result from a variety of causes. Many children with autism, she said, have aversions to certain foods. Some will insist on eating the same foods nearly every day, to the exclusion of other foods. So while they may consume enough calories to meet their needs—or even more calories than they need—they may lack certain nutrients, like calcium and vitamin D.

Other children with autism may have digestive problems which interfere with the absorption of nutrients. Moreover, many children with autism remain indoors because they require supervision during outdoor activity. Lack of exercise hinders proper bone development, she said. Similarly, if children remain indoors and are not exposed to sunlight, they may not make enough vitamin D, which is needed to process calcium into bones. The boys in the study who were on a casein-free diet had the thinnest bones. In fact, the 9 boys who were on a casein-free diet had bones that were 20 percent thinner than normal for children their age. Boys who were not on a casein-free diet showed a 10 percent decrease in bone thickness when compared to boys with normal bone development.

The study authors wrote that bone development of children on casein-free diets should be monitored very carefully. They noted that studies of casein-free diets had not proven the diets to be effective in treating the symptoms of autism or ASD.

Only 9 boys on casein-free diets were available to participate in the study, Dr. Hediger said. When conducting a scientific study, it’s easier to obtain statistically valid results by studying a larger number of individuals than with a smaller number of individuals. However, the dramatic difference in the boys’ bone thickness when they were either on a casein-free diet or an unrestricted diet and when compared to normally developing bones strongly suggest that the bone thinning the researchers observed was statistically valid.

The researchers recommended that larger studies be conducted to confirm their results.

Until those studies can be conducted, Dr. Hediger offered the following advice: “Our study shows that it couldn’t hurt—and would probably help—if parents of children with autism or autism spectrum disorder consulted with a dietitian during their children’s routine medical care to make sure that their diets are balanced.”

The study, by researchers from the National Institutes of Health and Cincinnati Children's Hospital Medical Center, was published online in the Journal of Autism and Developmental Disorders.