Water Fluoridation and Birth Outcomes in California

There is a lack of research on the relationship between water fluoridation and pregnancy outcomes.

We assessed whether hypothetical interventions to reduce fluoride levels would improve birth outcomes in California.

We linked California birth records from 2000 to 2018 to annual average fluoride levels by community water system. Fluoride levels were collected from consumer confidence reports using publicly available data and public record requests. We estimated the effects of a hypothetical intervention reducing water fluoride levels to $0.7\text{\hspace{0.17em}ppm}$ (the current level recommended by the US Department of Health and Human Services) and $0.5\text{\hspace{0.17em}ppm}$ (below the current recommendation) on birth weight, birth-weight-for-gestational age z-scores, gestational age, preterm birth, small-for-gestational age, large-for-gestational age, and macrosomia using linear regression with natural cubic splines and G-computation. Inference was calculated using a clustered bootstrap with Wald-type confidence intervals. We evaluated race/ethnicity, health insurance type, fetal sex, and arsenic levels as potential effect modifiers.

Fluoride levels ranged from 0 to $2.5\text{\hspace{0.17em}ppm}$, with a median of $0.51\text{\hspace{0.17em}ppm}$. There was a small negative association on birth weight with the hypothetical intervention to reduce fluoride levels to $0.7\text{\hspace{0.17em}ppm}$ [$-2.2g$; 95% confidence interval (CI): $-4.4$, 0.0] and to $0.5\text{\hspace{0.17em}ppm}$ ($-5.8g$; 95% CI: $-10.0$, $-1.6$). There were small negative associations with birth-weight-for-gestational-age z-scores for both hypothetical interventions ($0.7\text{\hspace{0.17em}ppm}$: $-0.004$; 95% CI: $-0.007$, 0.000 and $0.5\text{\hspace{0.17em}ppm}$: $-0.006$; 95% CI: $-0.013$, 0.000). We also observed small negative associations for risk of large-for-gestational age for both the hypothetical interventions to $0.7\text{\hspace{0.17em}ppm}$ [$\text{risk\hspace{0.17em}difference\hspace{0.17em}}\left(\text{RD}\right)=-0.001$; 95% CI: $-0.002$, 0.000 and $0.5\text{\hspace{0.17em}ppm}$ ($-0.001$; 95% CI: $-0.003$, 0.000)]. We did not observe any associations with preterm birth or with being small for gestational age for either hypothetical intervention. We did not observe any associations with risk of preterm birth or small-for-gestational age for either hypothetical intervention.

We estimated that a reduction in water fluoride levels would modestly decrease birth weight and birth-weight-for-gestational-age z-scores in California. https://doi.org/10.1289/EHP13732.