Children who drink bottled water have less lead in their blood but more decay in their teeth, researchers say. The finding reveals a possible pitfall for those seeking to avoid lead contamination from pipes.
“Elevated blood lead levels affect only a small minority of children, but the health consequences are profound and permanent,” said Anne E. Sanders, PhD, from the Dental Ecology Department at the University of North Carolina, Chapel Hill, in a news release. “On the other hand, tooth decay affects one in every two children, and its consequences, such as toothache, are immediate and costly to treat.”
Dr Sanders and Gary D. Slade, PhD, from the same department, published the finding online November 27 in the American Journal of Preventive Medicine.
Concerns about lead received renewed attention after the city of Flint, Michigan, changed the source of its drinking water, inadvertently flushing lead into water pipes. Blood lead levels increased in young children living in Flint, and in 2016, the Environmental Protection Agency advised people in Flint to drink filtered or bottled water.
Previous research has shown that fluoridated drinking water reduces the risk for caries; therefore, Dr Sanders and Dr Slade wanted to know how children would be affected by drinking bottled water instead of tap water.
They analyzed a nationally representative sample of 15,604 children and adolescents aged 2 to 19 years who participated in the National Health and Nutrition Examination Survey from 2005 to 2014. The survey is the US benchmark for national surveillance of blood lead levels and is the sole national source of dental examination data. Of those sampled, 12,373 records included data on blood lead level and 5677 included data on dental caries.
After an in-home interview, participants visited a mobile examination center, where they donated a blood sample, completed a dietary interview, and received a dental examination. About 15% of the children stated that they did not drink tap water, and those who did not drink tap water said they drank more bottled water.
The researchers defined elevated blood lead level as at least 3 μg/dL. This is lower than the threshold of at least 5 μg/dL recommended by the Centers for Disease Control and Prevention, based on blood lead levels in 2007 to 2010. But “the Council on Environmental Health now recognizes that there is no blood lead level without deleterious effects,” the researchers write. They defined caries as the presence of one of more decayed tooth surfaces.
The researchers did not find a simple correlation between drinking tap water and either blood lead level or caries when they looked at children of all ages.
However, when they looked at children by specific age group, they found that 6.9% of preschool children (children aged 2 to 5 years) who drink tap water had a blood lead level of at least 3 μg/dL compared with 4.0% of those who did not drink tap water, a significant difference (P = .012). In addition, 20.5% of preschool children who drank tap water had caries compared with 31.8% of those who did not drink tap water, which was also significant (P = .003).
And when they adjusted for the period when the children were surveyed, sex, age, ethnicity, and income, they found that children who did not drink tap water had 62% (adjusted prevalence ratio, 0.62; 95% confidence interval, 0.42 – 0.90) of the risk for elevated lead blood level and 1.13% (adjusted prevalence ratio, 1.13; 95% confidence interval, 1.03 – 1.23) of the risk for caries of children who did drink tap water.
Children who did not drink tap water were more likely to get caries even after the researchers adjusted for consumption of sugar-sweetened beverages.
In addition, children who drank tap water were more likely to have elevated blood lead levels regardless of whether they lived in older or newer houses.
Water drinking patterns varied by age and ethnicity. Among preschoolers, 21.3% did not drink tap water compared with 11.2% of adolescents (aged 12 – 19 years). Among Mexican-American children, the rate was 32.2% compared with 8.0% of non-Hispanic white children. Among children living below the poverty line, the rate was 22.6%.
The proportion of children drinking tap water did not change significantly over the years of the study, but blood lead levels declined, perhaps as a result of new regulations.
Overall, nearly 3% of children and adolescents had elevated blood lead levels and 49.8% had caries. The overall geometric mean blood level was 0.875 μg/dL (95% confidence interval, 0.865 – 0.885 μg/dL), with 2.9% of children exceeding blood lead levels of 3 μg/dL.
The fluoridation status of participants’ tap water was unknown, so the observation that drinking tap water protects against tooth decay may be an underestimate of fluoride’s protective effect, the researchers point out.
“Our study draws attention to a critical trade-off for parents: children who drink tap water are more likely to have elevated blood lead levels, yet children who avoid tap water are more likely to have tooth decay,” said Dr Slade in the press release.
The study was funded by the National Institutes of Health. The researchers have disclosed no relevant financial relationships.
Am J Prev Med. Published online November 27, 2017. Full text
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