According to a large Swedish study, the high probability of having large babies for their gestational age may be associated with fluoride intake in the perinatal period.
The authors write that the study of more than 500 mother-child couples is the first to suggest a correlation between fluoride exposure during pregnancy and birth size. The results obtained cannot be explained by the source of water or food consumed during pregnancy. The exceptions are tea and fruit, which may have had a weak but significant association with birth weight. The authors believe that the increase in weight and height of the child at birth may be associated with additional water intake.
“Our findings highlight the need for further research on the possible adverse effects of early fluoride exposure on the development and health of children,” write the authors, led by Maria Kippler, PhD, from the Karolinska Institute in Stockholm.
For years, fluoride has been added to oral care products and public water supplies to prevent tooth decay. In recent years, some researchers have raised concerns, explaining that fluoride intake can have a negative impact on children's development.
Recent studies have shown an association between adolescent kidney function and fluoride levels in drinking water, and a potential association between maternal exposure to fluoride and lower IQ and non-verbal deficits in children.
In addition, large babies at gestational age can cause complications for mother and baby. Babies with birth weights greater than the 90th percentile for their gestational age can lead to difficult births, birth injuries, and an increased incidence of birth defects.
To assess the impact of fluoride exposure during pregnancy on birth outcomes, researchers analyzed data from 558 mothers and their babies in the NICE (Influence of Diet on Immunological Maturation in Childhood in Relation to the Environment) cohort study. NICE is made up of families from northern Sweden recruited between 2015 and 2018.
An ion selective electrode measured maternal exposure to fluoride by assessing the urinary concentration of a known marker of ongoing exposure at 29 weeks' gestation. Weight, length, head circumference, and gestational age of infants at birth were obtained from hospital records.
The mean body length at birth was 50 cm for girls and 50.7 cm for boys. According to the study, the average head circumference was 34.6 cm for girls and 35.3 cm for boys, and the average birth weight was 3530 g for girls and 3640 g for boys.
Mean urinary fluoride concentration was 0.71 mg/l (5th-95th percentile 0.31-1.9 mg/l; adjusted for specific gravity). Each 1 mg/L increase in maternal urinary fluoride correlated with an average increase in birth weight of 84 g, length of 0.41 cm, and head circumference of 0.3 cm.
Of the children, 77 (28%) were born large for gestational age (90th percentile). Regression models showed that each 1 mg/L increase in maternal urinary fluoride was associated with an increased risk for the baby to be born large for gestational age (odds ratio = 1.39).
Tea consumption, especially black tea, has been associated with increased urinary fluoride concentrations in mothers. The fluoride concentration was also higher in winter and autumn samples, probably because more tea is consumed in cooler weather.
“Urine fluoride concentration did not correlate with food intake data, except for a weak positive correlation with tea, which may be the result of additional water intake and consumption of tea itself,” the authors write. “Black tea followed by green tea is known to contain more fluoride than other types of tea.”
Notably, the mean fluoride levels of more than 500 mothers were below the 1.5 mg/L limit recommended by the World Health Organization for the prevention of fluorosis. The study authors also noted that they controlled for “well-established determinants of birth size increase.”
However, the researchers noted several limitations. Although the authors had information on maternal obesity, they did not have data on maternal size at birth, which could affect the birth weight of the child. In addition, only one urine sample was taken in late pregnancy to assess urinary fluoride concentration. Although concentrations have been adjusted for specific gravity to account for differences in urine dilution, this may have led to misclassification of exposure due to bodily function in late pregnancy.
“Given the ubiquitous presence of fluoride in drinking water and the fact that having a large baby for gestational age is associated with perinatal complications, additional prospective cohort studies are needed to confirm our findings and elucidate the mechanisms by which fluoride may affect on intrauterine growth,” write Kippler et al.