Impact of fluoride on neurological development in children

불소가 어린이의 뇌발달에 미치는 영향

July 25, 2012 — For years health experts have been unable to agree on whether fluoride in the drinking water may be toxic to the developing human brain. Extremely high levels of fluoride are known to cause neurotoxicity in adults, and negative impacts on memory and learning have been reported in rodent studies, but little is known about the substance’s impact on children’s neurodevelopment. 매우 높은 고농도 불소가 성인들에게 뇌독성물질로 작용고 기억과 학습에 부정적인 영향을 미친다고 보고 된바 있다. 그러나 어린이들의 뇌발달에 미치는 영향에 대해 알려진바는 거의 없었다.

In a meta-analysis, researchers from Harvard School of Public Health (HSPH) and China Medical University in Shenyang for the first time combined 27 studies and found strong indications that fluoride may adversely affect cognitive development in children. Based on the findings, the authors say that this risk should not be ignored, and that more research on fluoride’s impact on the developing brain is warranted.

The study was published online in Environmental Health Perspectives on July 20, 2012.

The researchers conducted a systematic review of studies, almost all of which are from China where risks from fluoride are well-established. Fluoride is a naturally occurring substance in groundwater, and exposures to the chemical are increased in some parts of China. Virtually no human studies in this field have been conducted in the U.S., said lead author Anna Choi, research scientist in the Department of Environmental Health at HSPH.

Even though many of the studies on children in China differed in many ways or were incomplete, the authors consider the data compilation and joint analysis an important first step in evaluating the potential risk. “For the first time we have been able to do a comprehensive meta-analysis that has the potential for helping us plan better studies. We want to make sure that cognitive development is considered as a possible target for fluoride toxicity,” Choi said.

Choi and senior author Philippe Grandjean, adjunct professor of environmental health at HSPH, and their colleagues collated the epidemiological studies of children exposed to fluoride from drinking water. The China National Knowledge Infrastructure database also was included to locate studies published in Chinese journals. They then analyzed possible associations with IQ measures in more than 8,000 children of school age; all but one study suggested that high fluoride content in water may negatively affect cognitive development. 연구자들은 8천명이상의 취학아동들의 IQ수치와의 가능한 상관관계를 분석하였다: 한 연구를 제외한 모든 연구에서 물속의 고농도 불소가 인지발달에 부정적인 영향을 미칠 수 있다고 보고하였다.

The average loss in IQ was reported as a standardized weighted mean difference of 0.45, which would be approximately equivalent to seven IQ points for commonly used IQ scores with a standard deviation of 15.*  Some studies suggested that even slightly increased fluoride exposure could be toxic to the brain. Thus, children in high-fluoride areas had significantly lower IQ scores than those who lived in low-fluoride areas. The children studied were up to 14 years of age, but the investigators speculate that any toxic effect on brain development may have happened earlier, and that the brain may not be fully capable of compensating for the toxicity.저농도 불소지역에 비해 고농도 불소지역의 아이들의 IQ가 현저이 낮았다. 14세이하의 어린이를 대상으로 한 연구이며, 연구자들은 나이가 어릴 수록 뇌발달에 독성의 영향을 많이 받으며 이는 나이가 어릴 수록 독성을 감당할 수 없기 때문이라고 보고있다.

“Fluoride seems to fit in with lead, mercury, and other poisons that cause chemical brain drain,” Grandjean says. “The effect of each toxicant may seem small, but the combined damage on a population scale can be serious, especially because the brain power of the next generation is crucial to all of us.” 불소는 납, 수은, 기타 독성물질과 잘 결합하며 화학적으로 두뇌에 누출된다. 각각의 독성물질이 미치는 효과는 적을 수 있으나 인구규모와 결합한 손상은 심각할 수 있다.

* This sentence was updated on September 5, 2012.

Read a September 2012 statement by the authors.

** Learn more about the IQ measurements by HSPH’s Anna L. Choi and Philippe Grandjean in response to a letter to the journal published in the March 2013 (Vol. 121, No. 3) Environmental Health Perspectives.

Follow-up Fluoride Study Published

December 19, 2014 — As a follow-up, Philippe Grandjean, adjunct professor of environmental health at Harvard School of Public Health (HSPH), Anna Choi, research scientist in the Department of Environmental Health, and colleagues have published a pilot study of cognitive functions in Chinese children exposed to different levels of fluoride from drinking water.

The new paper, entitled “Association of lifetime exposure to fluoride and cognitive functions in Chinese children: A pilot study,” has been published online and in the January-February 2015 issue of Neurotoxicology and Teratology.

— Marge Dwyer 

메타분석(meta analysis)란

의학분야 혹은 교육학, 사회복지학 등 사회과학에서 한정적 실험결과의 일관성(consistency)을 검증하기 위한 분석방법으로 과거의 실험결과치를 이용해 어떤 실험결과를 일반화하는 분석을 의미한다.

즉, 실험결과를 이용한 논문들은 대부분 제한된 샘플(통제 및 실험집단 크기) 하에서 이루어지기 때문에 이를 과학적 명제 혹은 일반화가 어려운 것이 현실이다. 그래서 과거 수십편의 논문에 나타난 실험결과를 통계적 분석 대상의 관찰치로 전환하여 실험결과의 일반화를 시키는 분석이다.

보다 다른 의미로 보면, 모집단(population)에 대한 실험결과를 과거 논문의 관찰치(observation)을 이용해 모집단의 결과로 추정하는 방법이다.