Oral Care Science

Athletes and Fluoride: A Concern for Endurance Athletes

Why heavy training can turn a beneficial mineral into a daily overdose, and a simple routine to keep the upside without the excess.

Endurance athletes are a specific group who may take in too much fluoride each day. For most people, fluoride is beneficial. It helps prevent dental caries both systemically and topically, and it remains a cornerstone of preventive dentistry for people at high risk of decay.^2,3

Most fluoride exposure comes from three sources: community water fluoridation at 0.7 ppm, fluoridated toothpaste at 1,000 to 1,500 ppm (with prescription formulas reaching 5,000 ppm), and professional topical treatments applied in the dental office at concentrations as high as 22,600 ppm.^{1,2,3,4,5,13,14}

Changing recommendations for daily fluoride intake

In 2025, the European Food Safety Authority (EFSA) set a safe level of total daily fluoride intake at 3.3 mg/day for adults, including pregnant women. The goal was to protect against effects on the developing brain, thyroid function, and bone mineralization.⁶

This is much lower than the older United States standard. In 1997, the Institute of Medicine (IOM) set a Tolerable Upper Intake Level of 10 mg/day, derived as 0.10 mg of fluoride per kilogram of body weight per day.⁷

EFSA used a drinking water reference point of 1.5 mg/L. Above that concentration, studies showed higher rates of hypothyroidism and the early signs of neurodevelopmental deficits in children.^6,9,10 The 3.3 mg/day level for pregnant women was set specifically to protect the fetus from neurodevelopmental harm, and that same safe level was then extended to all adults and to children over 8 years of age.^6,8,11

The difference between the two standards comes down to what each one measured. The 1997 IOM number was based only on the risk of skeletal fluorosis, meaning fluoride building up in bone and making it more brittle. It did not account for thyroid or neurodevelopmental effects.⁷

Under the newer EFSA figure, many Europeans turned out to be exceeding the recommended intake, especially those consuming fluoridated salt, tea, or water with higher fluoride levels. One European estimate put total daily intake at 3.8 mg for adults, already above the 3.3 mg/day safe level.¹²

Fluoride exposure from toothpaste

In an ideal routine, fluoride is applied twice a day, once in the morning and once at night, using toothpaste at either 1,000 to 1,500 ppm or 5,000 ppm. The paste is either rinsed off or spit out without rinsing, and habits change how much fluoride a person actually takes in.

A full strip of toothpaste (about 1 g) at 1,000 to 1,100 ppm holds roughly 1.0 mg of fluoride. Most of that is spit out, and only about 0.1 to 0.3 mg is swallowed by accident per session.¹⁴ A full strip of 5,000 ppm paste holds about 5.0 mg of fluoride. These stronger pastes are usually used in smaller amounts and rinsed after brushing, but the amount swallowed is still higher than with regular paste.¹³

Brushing twice a day, daily fluoride intake from toothpaste alone comes to roughly 0.2 to 0.5 mg for over-the-counter paste, and possibly 0.5 to 1.0 mg or more for prescription-strength paste.

Fluoride exposure from drinking water

Over the course of a day, the average adult drinks about 2.7 to 3.7 L of total water (women and men, respectively).^15,16,17 At a fluoride concentration of 0.7 ppm, that works out to roughly 1.9 to 2.6 mg of fluoride per day from water alone (0.7 mg/L multiplied by 2.7 to 3.7 L). For people who drink well water or filtered water, fluoride from water may be close to zero.

The athlete's dilemma: much higher water intake

The real concern is how much water endurance athletes drink. Sweat rates during exercise run from 0.3 to 2.4 L per hour, depending on intensity, duration, fitness, heat acclimatization, and the environment.^18,19 Recommended fluid intake during exercise is 0.4 to 0.8 L per hour.¹⁸

On a hot day with long training, an endurance athlete's total daily water intake can reach 6 to 12 L or more. At 0.7 ppm, that comes to 4.2 to 8.4 mg of fluoride from drinking water alone. That already passes the EFSA safe level of 3.3 mg/day and approaches or exceeds the 1997 IOM limit of 10 mg/day.^6,7

The problem is compounded by how the body handles fluoride during exercise, because exertion does not raise fluoride excretion in proportion to intake. A pilot study found that moderate and vigorous exercise raised plasma fluoride and pointed toward reduced renal fluoride clearance (13.1 mL/min during moderate exercise versus 26.5 mL/min at rest).²⁰ A follow-up crossover study confirmed that moderate exercise significantly raised peak plasma fluoride (226 ng/mL versus 27 ng/mL at rest).²¹

In other words, even though athletes drink more and produce more urine, the body does not excrete the extra fluoride at the same rate. It is retained, and it stays available to produce biological effects.

Fluoride and the thyroid

Fluoride in drinking water above roughly 2.5 mg/L has been shown to affect thyroid function. A dose-response meta-analysis of 27 studies found that TSH (thyroid-stimulating hormone) began to rise in a roughly linear way at water fluoride around 2.5 mg/L, with a mean TSH difference of 1.05 µIU/mL between the highest and lowest exposure groups.⁹

Most studies agree that sodium fluoride raises TSH and lowers T3 and T4, the pattern seen in hypothyroidism.²² The mechanism has a few parts. Fluoride interferes with iodine metabolism by displacing iodine in the thyroid and blocking its uptake. It also drives oxidative stress and turns down thyroid-related genes, and the result is lower thyroid hormone production.²²

A Canadian pregnancy cohort study found that a 0.5 mg/L rise in drinking water fluoride was linked to 1.65 times higher odds of primary hypothyroidism. Among women without thyroid autoimmunity, the link was stronger still (odds ratio 2.85).¹⁰ Children born to mothers with fluoride-associated primary hypothyroidism had lower IQ scores, and the effect was larger in boys (a drop of 8.42 points).¹⁰ EFSA concluded that the 3.3 mg/day safe level protects against the thyroid effects seen above 1.5 mg/L in water.⁶

This matters for athletes. Someone drinking 6 to 12 L of fluoridated water a day could reach total fluoride exposures that fall into the range tied to thyroid disruption. The water itself stays at 0.7 ppm, but the total daily dose of 4.2 to 8.4 mg from water, added to toothpaste and diet, may produce cumulative effects similar to those seen at higher water concentrations. This has not been studied directly in athletes, but the data showing greater fluoride retention during exercise makes it a biologically plausible concern.^20,21

Fluoride and bone

No study has directly tied fluoride exposure to bone outcomes in cyclists, but two well-established findings point in the same direction.

First, cyclists tend to have low bone mineral density (BMD) because their sport is not weight-bearing.^23,24 Second, high fluoride causes skeletal fluorosis, a paradox in which bone density goes up while bone quality drops and fracture risk rises.^25,26,27

A landmark trial found that sodium fluoride therapy raised lumbar spine BMD by 35% but lowered cortical bone density by 4% at the radial shaft, and fractures outside the spine were significantly higher in the fluoride group (72 versus 24).²⁵ A dose-response meta-analysis found that fracture risk climbs above roughly 1.5 mg/L of fluoride in water, with risk ratios of 1.06, 1.19, and 1.35 at 2.0, 3.0, and 4.0 mg/L.²⁶

A practical starting point

The main benefit of fluoride in adults is caries prevention. For endurance athletes, that benefit still applies, and it matters even more, because high carbohydrate intake and frequent acidic exposures during training raise the risk to enamel.

On that last point, for athletes who want to further reduce fluoride exposure, a nanohydroxyapatite (n-HAp) toothpaste may be worth considering as an alternative. Recent clinical trials have found that hydroxyapatite toothpaste is non-inferior to 1,450 ppm fluoride toothpaste for caries prevention in adults, and systematic reviews support its effectiveness as an anti-caries agent.^28,29,30 Using n-HAp paste before consuming carbohydrates could offer enamel protection without adding to a person's fluoride burden.

A dentist can adjust this protocol, but it gives a reasonable starting point.