I recently researched the risks of fluoride in tea for a blog post, after a group discussion raised the issue. To be clear, the probable risk is low. I’ll return to special cases where there might be real risks after filling in some basics.
Fluoride is a positive dietary input found in tea, recognized as helping prevent tooth decay, and cited as one form of treatment for osteoporosis (a WebMD reference to that, and some general background). But any dietary or supplementary inputs are beneficial or harmful within a limited range, and the focus here is on risks related to too much.
Basics related to Fluoride intake
-The earlier EPA recognized limit for fluoride daily intake was 10 mg / day.
-That was revised to .08 mg fluoride / kg (body weight) / day. Since I weigh 70 kilograms (155 pounds) 5.6 mg / day of fluoride is the long term limit.
See an EPA Questions and Answers on Fluoride reference and FLUORIDE IN DRINKING WATER: A Scientific Review of EPA’s Standards for more background.
-The treatment level of fluoride (added to municipal water) is .7 to 1.2 mg / liter (or ppm, parts per million; they work out to mean the same thing).
-Since fluoride occurs naturally in some water sources (wells or springs; it is just another mineral) the EPA sets a limit for a maximum. They now recommend municipal water sources should contain no more than 2 mg / liter (a revised guideline), with a mandatory regulated limit of 4 mg / liter.
-Some natural water sources can contain over 10 mg / liter, although that is relatively rare.
Fluoride in tea
An Indian research paper provides a great starting point for amounts of fluoride in brewed teas:
That amount varies from 1 mg / liter up to around 3.5 mg / liter.
This table shows amounts of fluoride in different Chinese teas measured as amounts in milligrams per kilogram of dry tea (from “Fluoride Content in Tea and Its Relationship With Tea Quality“):
A bit of interpretation is required. I do a lot more with the numbers and calculations in that earlier post but we can estimate brewed tea amounts from this, after some assumptions:
-50 to 100 mg fluoride / kg of tea are considered as low and high levels
-each cup of brewed tea is based on two grams of dry tea (not a given, but making 2 cups of tea using 4 grams of dry tea is within the standard range). Essentially complete extraction is assumed here, not really a given in actual practice.
50 mg / kg tea * 2 gm of tea per cup * 1 kg of dry tea / 1000 grams =
.1 mg / cup of tea (or .2, based on the “100” value; up to .4, based on the very highest “200” range)
Sounds like not much. Even if those are 6 ounce cups of tea it still only works out to 1.1 mg / liter on that higher “100 mg / kg” calculation (for over five cups of tea):
This estimation matches the Indian study relatively well (1-3.5 mg / liter of tea), with a range up to 2.2 mg / liter using that highest “200” value instead.
Additional thoughts / conclusions
Based only on the amount of fluoride in water there is almost no risk. Drinking two liters of water a day treated to 1.2 mg / liter (the highest treatment level) adds up to 2.4 mg; well below either limit of 5 or 10 mg / day. The recommended EPA city water maximum limit of 2 mg / day brings that to 4 mg / day (and the mandatory treatment level to double that, giving alarmists something to talk about, since that is a bit high).
Based only on normal consumption of relatively high amounts of tea (two liters per day) there is very little risk. Even at the very highest level those totals don’t exceed 7 mg / day, for the Indian study values, or 4.4 mg / day for the highest Chinese version. But then averaging drinking two liters of tea per day really is a lot; that’s a bit over eight 8-ounce cups of tea.
The obvious case when there could be some limited risk: when both add up. Preparing two liters of tea per day from fluoride treated water really could relate to an intake of 2.4 + 4-7 mg / day, on the highest side a good bit above the maximum long term intake for someone of my weight (5.6 mg / day), approaching the older recognized limit of 10 mg / day.
Other special cases: high levels in natural water sources, or due to a recreational runner or construction worker drinking a lot of treated water.
Per online discussion there could be much higher risk related to some types of hei cha. Those Indian study results seems to match that, with better teas relatively low in levels (more often based on two leaves and a bud plucking), with CTC teas made from other leaves. Based on that other research there is potential for much higher fluoride levels for teas made using more of the oldest leaves.
My personal conclusion: there is nothing to worry about, beyond those few special cases.