Junkfood Science: Cavities and kids

April 06, 2008

Cavities and kids

According to popular wisdom, childhood obesity is caused by eating too much junkfood, sweets and sodas, so fat kids must have more cavities, right? The findings of another study looking for links between bad behaviors and obesity weren’t what everyone was sure they would find. Researchers and journalists are struggling to make sense of it. No one has noticed the answers are right there and the findings aren’t a surprise at all.

In one study* published in the new issue of Community Dentistry & Oral Epidemiology, dental researchers at the Eastman Dental Center at the University of Rochester Medical Center did a secondary analysis of dental and physical exams done on children 2 to 18 years of age who’d participated in the National Health and Nutrition Examination Survey, NHANES III (1988-1994) and 1999–2002 NHANES. “The purpose of this study was to examine the association between dental caries and being at risk of overweight and being overweight,” wrote the authors.

In their introduction, they described their working assumptions:

· The prevalence of overweight children in the United States has been increasing steadily over recent years.

· Childhood overweight is unhealthy and “usually a result of an imbalance between energy intake and energy expenditure.”

· Fatness in children is associated with higher intakes of refined carbohydrates, especially sugars, as are higher dental caries.

Based on these premises — which, as we know, are popular fallacies — they used dental data on a total of 17,748 American children and made BMI their “primary explanatory variable of interest,” looking to enumerate the link.

“We expected to find more oral disease in overweight children of all ages, given the similar causal factors that are generally associated with obesity and caries,” the lead author, Dorota Kopycka-Kedzierawski, DDS, MPH, said in a press release.

Instead, they found “no evidence to suggest that overweight children are at increased risk for dental caries.” Among the 2 to 5 year olds, there was no difference in tooth decay in their baby teeth among all weight ranges. Among the children 6 to 18 years of age, the ‘overweight’ children in NHANES III were less likely to have cavities in their baby and permanent teeth compared to ‘normal’ weight peers. In fact, the fat kids were half as likely to have cavities. And in the 1999-2002 NHANES, there was no difference in cavities among the children 6 to 18 years of age at any weight range. No correlation between weight and cavities at all.

They concluded:

In conclusion, these data from two separate, nationally representative samples of children and youth provide no evidence that overweight or at risk for overweight children and youth are at increased risk for dental caries and provide some, but inconsistent, evidence that overweight status may be associated with a decreased risk for dental caries.

The authors were surprised by their findings, though, and because they couldn’t explain them, determined that their analysis was inconclusive:

These findings surprised us; a priori, we posited that overweight should be associated with dental caries, as obesity and caries are, in principle, influenced by similar factors. Our analyses are inconclusive as to whether or not there is a relationship between increased BMI and decreased caries in US children and adolescents. We can only speculate as to why this is.

In analyzing their findings, however, their focus wasn’t on explaining children’s cavities, but why the fat children were fat! Perhaps, they are eating foods higher in fat rather than sugars, they wrote. Or, perhaps, “dietary practices are not the only possible factors that contribute to the obesity epidemic among U.S. children and adolescents.” They proposed that sedentary activity and television viewing could primarily “be to blame.”

“Our findings raise more questions than answers,” Dr. Kopycka-Kedzierawski, said. “Research to analyze both diet and lifestyle is needed to better understand the results.”

Blind spots

Their findings didn’t actually raise more questions. In fact, they confirmed what has been already been recognized in the medical literature and by expert bodies. Let’s take another look at this study, as well as the available evidence, and see what it reveals.

As the Eastman dentists described, among nearly 15 years of health examinations on U.S. children, there is no correlation between body weights and dental caries. Contrary to the authors' working premises, however, decades of the soundest clinical and epidemiological evidence and expert reviews, covered extensively at JFS, have preponderantly shown that fat and thin children eat and behave no differently to explain the natural diversity in their sizes, nor do parents of fat children feed their children nutritionally different diets than those of thin children, and the same goes for poor parents compared to ones of privilege. The CDC’s National Center for Health Statistics has also reported that there have been no significant increases in the numbers of U.S. children considered ‘overweight’ since 1999-2000.

The first step to learning how we can most help to improve the dental health of children would be to move past popular beliefs and the incessant pursuit of things to blame on fat children. Both can leave us blind to the evidence that can guide us to sound solutions.

On April 30, 2007, the National Center for Health Statistics released the most comprehensive assessment of oral health data available on the U.S. population to date, in its report “Trends on Oral Health Status.” [Covered here.] For this 104-page report, the CDC compiled data from NHANES surveys from 1988-1994 to 1999-2004 and found “significant decreases... in the prevalence of tooth decay in the permanent teeth for children, teens and adults.” Among ages 12-18, for example, the prevalence of tooth decay had dropped from 68% to 59% during these years. By comparison, 90.4% of kids in the early 1970s had dental cavities! Clearly, there’s already little evidence to support fears that modern dietary or weight changes among the population are related to major harmful effects on children’s teeth.

In fact, in examining contributing factors, sugar was not even mentioned in the CDC’s oral health report; nor were processed foods, snacks or sugary drinks. Not once. Despite the popularity of beliefs that sugary or “processed” foods are a major cause of cavities, public health experts long ago moved beyond dietary recommendations for the primary prevention of cavities among the public. When the scientific evidence on sugar and carbohydrates was examined during the development of the 2005 Dietary Guidelines for the U.S. Department Health and Human Services, for instance, the evidence on sugar and sugary drinks as promoting dental cavities came up short. Numerous studies have even found no relationship, but the bottom line is that the CDC concluded that carbohydrates have less significant roles than dental care.

The Canadian Task Force and U.S. Preventive Services Task Force, after their comprehensive reviews of the evidence, similarly concluded that dietary recommendations to reduce sugar intake have poor evidence for effectiveness. Most surprising, both Task Forces found little evidence that toothbrushing or flossing, as ordinarily practiced, reduce cavities, although they continue to recommend both for good hygiene and to help control gum disease.

The single greatest risk factor for dental caries among young people is ... social-economic class. While the overall prevalence of caries has dropped among American children overall, it continues to be highest among the poorest children. Concurring with other population studies, the CDC report found that dental caries among U.S. children and teens varies most significantly by poverty status reflective of access to preventive dental services, most notably dental sealants. As the use of sealants and professional dental care increases, cavities among those children significantly drop. Not only do the poorest children have considerably fewer dental sealants compared to well-off children (families over 100% of the poverty level), the CDC report found, but they have three times the unfilled cavities.

In this new study by the dentists at Eastman Dental Services, their analysis of NHANES 1999-2002 dental exams found no correlation with dental caries and children’s weights. But their data showed one factor that had the most significant correlation to increased risk of cavities in U.S. children: living in poverty (<100% poverty level).

The risks for caries associated with poverty were 240% as high among children under age 12, and 80% higher among older children ages 12-18, compared to those in homes above the 200% poverty level.

Yet, parents and the public never heard this or had the opportunity to learn from it how we might most be able to help children. Surprisingly, the dental researchers didn’t include dental sealants among the confounding factors they considered, as they focused on childhood ‘overweight.’

Children’s body weights do not cause cavities — there isn’t even a correlation, nor is it biologically plausible given what is known about both. Decades of evidence among American children have consistently shown that we can most help them enjoy better oral health by improving access to preventive dentistry... if we see it.

© 2008 Sandy Szwarc

* Researchers in another dental study published in the journal Community Dentistry & Oral Epidemiology which hasn’t been mentioned in the news, also seemed to struggle with their findings. Led by Elisabeth Wärnberg Gerdin, Center for Public Health Sciences, County Council of Östergötland in Sweden, the authors examined caries data on 2,303 children born in 1991 and the associations with their BMIs. Children in the county of Östergötland are “called for regular dental check-ups from age 3 to 20 years,” and they also had their physical measurements taken by trained nurses. The authors found: “Caries prevalence decreased with increasing socioeconomic status at all ages, whereas childhood BMI and proportion of overweight/obese children were unrelated to socioeconomic status.”

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