Environ Int. 2019 Nov 16;134:105315. doi: 10.1016/j.envint.2019.105315. [Epub ahead of print]

Fluoride exposure from infant formula and child IQ in a Canadian birth cohort.

Till C¹, Green R², Flora D², Hornung R³, Martinez-Mier EA⁴, Blazer M², Farmus L², Ayotte P⁵, Muckle G⁶, Lanphear B⁷.

Author information

1

Faculty of Health, York University, Ontario, Canada. Electronic address: ctill@yorku.ca.

2

Faculty of Health, York University, Ontario, Canada.

3

Pediatrics and Environmental Health, Cincinnati Children's Hospital Medical Center, OH, USA.

4

School of Dentistry, Indiana University, IN, USA.

5

Centre de Recherche du CHU de Québec, Université Laval, Québec, Canada; Department of Social and Preventive Medicine, Laval University, Quebec, Canada.

6

Centre de Recherche du CHU de Québec, Université Laval, Québec, Canada; School of Psychology, Laval University, Quebec, Canada.

7

Faculty of Health Sciences, Simon Fraser University, British Columbia, Canada; Child & Family Research Institute, BC Children's Hospital, University of British Columbia, Canada.

Abstract

BACKGROUND:

Infant consumption of formula reconstituted with fluoridated water can lead to excessive fluoride intake. We examined the association between fluoride exposure in infancy and intellectual ability in children who lived in fluoridated or non-fluoridated cities in Canada.

METHODS:

We examined 398 mother-child dyads in the Maternal-Infant Research on Environmental Chemicals cohort who reported drinking tap water. We estimated water fluoride concentration using municipal water reports. We used linear regression to analyze the association between fluoride exposure and IQ scores, measured by the Wechsler Primary and Preschool Scale of Intelligence-III at 3-4 years. We examined whether feeding status (breast-fed versus formula-fed) modified the impact of water fluoride and if fluoride exposure during fetal development attenuated this effect. A second model estimated the association between fluoride intake from formula and child IQ.

RESULTS:

Thirty-eight percent of mother-child dyads lived in fluoridated communities. An increase of 0.5 mg/L in water fluoride concentration (approximately equaling the difference between fluoridated and non-fluoridated regions) corresponded to a 9.3- and 6.2-point decrement in Performance IQ among formula-fed (95% CI: -13.77, -4.76) and breast-fed children (95% CI: -10.45, -1.94). The association between water fluoride concentration and Performance IQ remained significant after controlling for fetal fluoride exposure among formula-fed (B = -7.93, 95% CI: -12.84, -3.01) and breastfed children (B = -6.30, 95% CI: -10.92, -1.68). A 0.5 mg increase in fluoride intake from infant formula corresponded to an 8.8-point decrement in Performance IQ (95% CI: -14.18, -3.34) and this association remained significant after controlling for fetal fluoride exposure (B = -7.62, 95% CI: -13.64, -1.60).

CONCLUSIONS:

Exposure to increasing levels of fluoride in tap water was associated with diminished non-verbal intellectual abilities; the effect was more pronounced among formula-fed children.

수돗물의 불소수치 증가 수치는 비언어적 지적능력의 감퇴와 관련이 있다.

Environ Int. 2019 Nov 4;134:105229. doi: 10.1016/j.envint.2019.105229. [Epub ahead of print]

Thyroid function, intelligence, and low-moderate fluoride exposure among Chinese school-age children.

Wang M¹, Liu L¹, Li H², Li Y³, Liu H⁴, Hou C⁴, Zeng Q⁴, Li P¹, Zhao Q¹, Dong L¹, Zhou G¹, Yu X⁵, Liu L⁵, Guan Q⁶, Zhang S⁷, Wang A⁸.

Author information

1

Department of Occupational and Environmental Health, Ministry of Education Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, PR China.

2

Department of Laboratory Medicine, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, PR China.

3

Tianjin Baodi District Centers for Disease Control and Prevention, Tianjin, PR China.

4

Tianjin Centers for Disease Control and Prevention, Tianjin, PR China.

5

Department of Epidemiology and Biostatistics, Ministry of Education Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, PR China.

6

Department of Laboratory Medicine, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, PR China. Electronic address: Guanq2000@126.com.

7

Department of Occupational and Environmental Health, Ministry of Education Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, PR China. Electronic address: shunzhang@hust.edu.cn.

8

Department of Occupational and Environmental Health, Ministry of Education Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, PR China. Electronic address: wangaiguo@mails.tjmu.edu.cn.

Abstract

BACKGROUND:

Thyroid hormones (THs) are critical for brain development. Whether low-moderate fluoride exposure affects thyroid function and what the impact is on children's intelligence remain elusive.

OBJECTIVES:

We conducted a cross-sectional study to examine the associations between low-moderate fluoride exposure and thyroid function in relation to children's intelligence.

METHODS:

We recruited 571 resident children, aged 7-13 years, randomly from endemic and non-endemic fluorosis areas in Tianjin, China. We measured fluoride concentrations in drinking water and urine using the national standardized ion selective electrode method. Thyroid function was evaluated through the measurements of basal THs [(total triiodothyronine (TT₃), total thyronine (TT₄), free triiodothyronine (FT₃), free thyronine (FT₄)] and thyroid-stimulating hormone (TSH) levels in serum. Multivariable linear and logistical regression models were used to assess associations among fluoride exposure, thyroid function and IQ scores.

RESULTS:

In adjusted models, every 1 mg/L increment of water fluoride was associated with 0.13 uIU/mL increase in TSH. Every 1 mg/L increment of urinary fluoride was associated with 0.09 ug/dL decrease in TT₄, 0.009 ng/dL decrease in FT₄ and 0.11 uIU/mL increase in TSH. Fluoride exposure was inversely related to IQ scores (B = -1.587; 95% CI: -2.607, -0.568 for water fluoride and B = -1.214; 95% CI: -1.987, -0.442 for urinary fluoride). Higher TT₃, FT₃ were related to the increased odds of children having high normal intelligence (OR = 3.407, 95% CI: 1.044, 11.120 for TT₃; OR = 3.277, 95% CI: 1.621, 6.623 for FT₃). We detected a significant modification effect by TSH on the association between urinary fluoride and IQ scores, without mediation by THs.

CONCLUSIONS:

Our study suggests low-moderate fluoride exposure is associated with alterations in childhood thyroid function that may modify the association between fluoride and intelligence.