Wednesday, August 30, 2017

Fluoride in tea; a summary version

Originally posted as:

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.

Editor's note:  that earlier article went through more related to possible health risks, factors relating to fluoride levels in tea, particularly related to the age of leaves used (bud and first two leaves versus "lower" leaves, which are higher in fluoride content), and calculations related to assessing intake.  This article version is a shorter summary.

Fluoride is a positive dietary input found in tea, recognized as helping prevent teeth 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.

Naturally occurring fluoride levels chart, places over 1.5 mg/liter supplement levels (source credit)

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.

more results from the earlier Chinese leaves study

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.

Editing note:  in reviewing a related issue I ran across the following reference for measured amounts in different teas, in the paper Assessment of fluoride concentration and daily intake by
human from tea and herbal infusions:

Some thoughts / interpretation:

-this matches the Indian tea study, with the general range of results of significantly under 1 mg / liter (starting at 1 mg / liter in that study, with the lowest range here roughly half that) up to over 3 mg / liter in some cases.

-a five or ten minute infusion time would match ordinary brewing practices; using a 30 minute brewing time is not typical.  For cases of cold brewing or brewing "grandpa style" (allowing tea to remain in contact with water) this higher level of fluoride extraction may result.

-lowest amounts are for buds-only or bud related teas, as expected (see the earlier related post).

-I hoped to review hei cha levels but they aren't included, except for pu'er, with those teas sampled all relatively low in fluoride level (.57 to 1.04 mg / liter based on 10 minute infusion time).

-oddly "Lipton" tea measured the second highest recorded level, and "Tetley Earl Grey" the third, after one outlier, Ygara Asta black tea.  Those Lipton and Tetley values are around the highest range for the Indian study (around 3 mg / liter), with the Ygara Astra in the range of double that (all varying by infusion time).

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