Fluoride (Sodium Fluoride / Fluoride Ion)

Fluoride is the ionic form of fluorine — the most electronegative element — and occurs naturally in groundwater from dissolution of fluoride-containing minerals (fluorite, apatite) [1]. Natural fluoride in groundwater ranges from trace amounts to 10+ mg/L in volcanic regions; communities with high natural fluoride (India, East Africa, China) have experienced endemic skeletal fluorosis for centuries [2]. In 1945, Grand Rapids, Michigan became the first city to intentionally add fluoride to drinking water at 1 mg/L, based on studies linking naturally fluoridated water to lower dental caries rates. By 1960, water fluoridation had become standard practice across the U.S. [1]. The recommended level has since been lowered to 0.7 mg/L (2015 revision) as dietary fluoride from other sources (toothpaste, food) increased. Industrial fluoride contamination comes from aluminum smelting, phosphate fertilizer production, and hydrogen fluoride manufacturing [2].

Fluoridated drinking water is the largest source for most Americans — providing 60-70% of total intake at 0.7 mg/L [1]. Dental products (fluoride toothpaste, fluoride rinses, professional fluoride treatments) add to intake, particularly if swallowed by young children [2]. Fluoride in food varies — tea (especially brick tea), marine fish, and canned goods processed with fluoridated water are higher sources [1]. Industrial exposure occurs near aluminum smelters, fertilizer plants, and HF manufacturing [2].

The dose-response relationship for fluoride is U-shaped: insufficient fluoride allows dental caries; optimal fluoride prevents cavities; excess causes dental fluorosis (mottled enamel), skeletal fluorosis, and potentially thyroid and neurological effects [1]. Dental fluorosis — white spots or pitting on enamel — affects 40% of U.S. adolescents at current exposure levels and is primarily a cosmetic concern at mild grades [2]. Skeletal fluorosis from chronic high-dose exposure (>4 mg/L) causes joint pain, bone fragility, and neurological complications. A 2020 National Toxicology Program systematic review found 'moderate confidence' that fluoride is associated with lower IQ in children at exposures above current U.S. levels, though this remains debated [1]. Fluoride inhibits thyroid peroxidase, raising concern about thyroid function at higher exposures [2].

Infants fed formula reconstituted with fluoridated tap water receive the highest dose per body weight — the CDC recommends using low-fluoride water for infant formula [1]. Children during tooth development (0-8 years) are susceptible to dental fluorosis from excessive fluoride intake [2]. People in regions with naturally high fluoride groundwater (> 2 mg/L) are at risk for skeletal fluorosis. Workers in aluminum smelting and fluoride chemical manufacturing face occupational high-dose exposure [1]. People with kidney disease excrete fluoride less efficiently and accumulate higher body burdens at equivalent intakes [2].

1. If you have an infant, use low-fluoride water (labeled drinking water with fluoride < 0.7 mg/L, or filtered water using reverse osmosis which removes fluoride) for formula reconstitution [1]. 2. Teach children to spit, not swallow, toothpaste — use only a rice-grain amount for children under 3 [2]. 3. If you have well water, test for naturally occurring fluoride — EPA has a secondary maximum contaminant level of 2 mg/L for aesthetics, with 4 mg/L as the enforceable MCL [1]. 4. Reverse osmosis (RO) filters effectively remove fluoride from drinking water; standard activated carbon filters do not remove fluoride efficiently [2]. 5. Reduce very high tea consumption if you're concerned — particularly dark or brick teas which are highest in fluoride [1].