Fluoride

Fluoride is not classically essential — no fluoride-dependent enzyme has been identified — but it substitutes for hydroxyl groups in bone and tooth enamel to form fluorapatite, which is more acid-resistant than hydroxyapatite. This is why fluoride is one of the most successful public-health interventions of the 20th century for dental caries.

Daily Adequate Intake

• Adult men: 4 mg/day.
• Adult women: 3 mg/day.
• Pregnancy / lactation: 3 mg/day.
• Tolerable Upper Intake Level: 10 mg/day for adults; lower for children (2.2 mg/day for age 4–8) to reduce dental fluorosis risk.

Water fluoridation

US Public Health Service recommends 0.7 mg/L in community water (lowered from the historical 0.7–1.2 range in 2015 as toothpaste availability has increased). CDC estimates fluoridation reduces childhood caries by 25% in kids and adults. The York Review (2000) and Cochrane 2015 confirm caries reduction but note the evidence is largely from pre-1975 studies before fluoride toothpaste became universal.

Dental fluorosis

Excess fluoride during tooth formation (age < 8) causes enamel hypomineralisation — white streaks in mild cases, brown pits in severe. Cosmetic, not functional. Rates have risen with widespread fluoride toothpaste use — pea-sized amount, spitting not swallowing, and supervised brushing in young children keep the risk low.

Skeletal fluorosis

Chronic intake > 10 mg/day for years causes bone pain, joint stiffness, and spinal ligament calcification. Endemic in parts of India, China, and East Africa where groundwater fluoride exceeds 3–5 mg/L. Not a public-health issue in fluoridated water systems at 0.7 mg/L.

Toothpaste and topical use

Fluoride toothpaste (1,000–1,500 ppm) is the single strongest evidence base for dental caries prevention (Cochrane 2010 — 26% caries reduction across 79 trials). Higher-concentration prescription pastes (5,000 ppm) are used for high-risk adults. Topical action (enamel remineralisation) outweighs systemic action in older children and adults.

The IQ controversy

Several recent observational studies (Green 2019; Bashash 2017) have reported small IQ decrements associated with prenatal fluoride exposure at community fluoridation levels. The findings are contested — methodological concerns, unadjusted confounders, and results not replicated in comparable populations. Systematic reviews conclude the strongest evidence for cognitive harm applies to groundwater levels much higher than fluoridated water. The debate is ongoing; major public health bodies (WHO, CDC, ADA) currently continue to endorse fluoridation at 0.7 mg/L.

Sources

• Fluoridated tap water (1 L): 0.7 mg
• Black tea (1 cup): 0.2–0.4 mg
• Green tea (1 cup): 0.1–0.3 mg
• Grapes and raisins: variable (residual insecticide fluoride)
• Marine fish (3 oz): 0.02–0.05 mg
• Bottled water — varies from 0 to over 1 mg/L; not standardised
• Fluoride toothpaste (pea-sized, adult): ~1 mg, most spit out