Fluoride exposure and duration and quality of sleep in a Canadian cohort

Abstract

Background: Research suggests that fluoride from dietary and environmental sources may concentrate in calcium-containing regions of the body such as the pineal gland. The pineal gland synthesizes melatonin, a hormone that regulates the sleep-wake cycle. We used population-based data from Cycle 3 (2012-2013) of the Canadian Health Measures Survey (CMHS) to examine associations between fluoride exposure and sleep outcomes.Methods: The sample included participants aged 16 to 79 years. Fluoride concentrations were measured in urinary spot samples (n=1303) and household tap water among those who reported drinking tap water (n=1016); urinary fluoride was adjusted for specific gravity (UFSG). We used multinomial and ordered logistic regression analyses to examine associations of fluoride exposure with self-reported sleep outcomes, including sleep duration and frequency of sleep problems. Sleep duration was classified as normal, low, or high according to age-based recommendations by the National Sleep Foundation, and frequency of sleep problems were measured on a 5-point scale, ranging from “never” to “all of the time”. Covariates were based on theoretical relevance and included age, sex, ethnicity, body mass index, and household income.Results: Median (IQR) UFSG and water fluoride concentrations were 0.67 (0.63) and 0.12 (0.38) mg/L, respectively; 32% of participants lived in communities supplied with fluoridated municipal water. A 0.5 mg/L increase in water fluoride level was associated with 34% higher relative risk of reporting sleeping less than the recommended duration [RRR = 1.34, 95% CI: 1.03, 1.73; p = .026]. UFSG was not significantly associated with sleep duration. Water fluoride and UFSG concentration were not significantly associated with frequency of sleep problems. Including chronic health conditions as a covariate did not substantially change the association between water fluoride and sleep duration.Conclusions: Fluoride exposure may contribute to sleeping less than the recommended duration among older adolescents and adults in Canada.