We have received several questions about Green Tea for dogs over the past couple of weeks, which is the reason for writing this post.
We feel that there is certain information that you need to know before you start giving your dogs green tea. This isn’t meant to scare or prevent you from giving green tea it is just to make you aware. This is also specific to green tea, as there are hundreds or different teas, and each one differs in the nutrtional properties they provide.
Green Tea does have several potential benefits. Some have more evidence than others. While green tea has the potential to aid in our dog’s health and well-being; there is too much of a good thing.
In one study that has demonstrated the potential benefits of green tea they were being given between 105 and 210 mgs of EGCG/kg bw per day.
The study was conducted over the course of 12 weeks. The dogs were fed a high fat diet. The results of the study demonstrated that tea polyphenols may act as a therapeutic agent for obesity, liver inflammation, and fat degeneration. (Rahman, et al 2020)
I can’t go into the full details as to the potential health benefits of green tea, because as a company we would be making health claims according to the State of California, as many of the potential benefits are not function claims, and many of them haven’t been demonstrated in canine studies.
That being said there are some risks associated with Green Tea.
The study was originally supposed to be over the course of 9 months. The Study ended at 6.5 months due to unexpected morbidity and mortality.
The study involved Beagles consuming (0, 200, 500, and 1000 mg/kg/day) of green tea extract. The dogs were given the extract fasted due to suspected increased bioavailability.
“Toxicity was evident by day 9 when clinical signs, including one death, significant body weight and food consumption decreases were seen in the 1000 mg/kg/day group. Dosing of that group was then discontinued and resumed one week later with 800 mg/kg/day after some body weight recovery. By the early termination of the study at 6.5 months, there were 16 deaths out of 24 PPE-treated animals.”(Kapetanovic et al 2009)
It should be noted that the majority of deaths occurred during the first 13 weeks and that males were more susceptible than females.
Several Standardized Green Tea extract-caused toxicities were observed.
- hematology (decreases in red blood cells, hemoglobin, and hematocrit, increases in white blood cells, neutrophils, monocytes, platelet count)
- Lesions in gastrointestinal tract, lymph nodes, liver, kidney, lung, heart and tonsils
- histopathology (epithelial necrosis in gastrointestinal tract, inflammation of the liver including centrilobular necrosis and congestion, renal tubular necrosis, atrophy of reproductive organs, and atrophy and necrosis of hematopoietic tissues)
- abnormalities in clinical chemistry, coagulation and urinalysis parameters
It was not clear to the researchers whether all or some of these issues were a direct or a secondary result due to dehydration, vomiting, diarrhea etc.
Furthermore, due to
“the high rate of mortality and morbidity, and manifestation of significant toxicities in multiple organs and systems, it was not possible to identify major cause(s) of toxicity or determine if incidences were dose-related.”(Kapetanovic et al 2009)
After the first study was stopped there was a second study that lasted a total of 13 weeks. The second study involved only male dogs receiving 200 mg/kg/day. The second study used a total of three different lots.
Two of the groups received the same lot from the first study the only difference was that one was given it in a fasted state while the other received it with food. The other two groups were given two different lots, both in a fasted state.
This time there were no mortalities, but two dogs did exhibit serious clinical signs during weeks 8 and 9. One of the dogs was found unresponsive to the touch and was administered oxygen to save his life.
All three groups being given the Green Tea extract fasted demonstrated signs of gastro-intestinal irritation, whether it was, vomiting, diarrhea and or red material in the run.
Surprisingly Lot A (the same as the first study showed the least toxicity.
“Overall, the toxicity was lower with the same dose and during the same time interval in this follow-up study than in the previous chronic study. Many of the same toxicities were seen in at least some animals in the two studies, but to a different extent. Evidence of digestive system disturbances, mild liver damage, moderate to progressive anemia (in individual animals that were not statistically significant between groups), mild disturbances in hematopoiesis (in liver, spleen, bone marrow), and transient ocular symptoms were seen in 1 to 3 animals in one or more PPE-treated groups and were more prevalent and pronounced with lots B and C in the 13-week study.”(Kapetanovic et al 2009)
In another 13 week study, the researchers determined that the NOAEL (No Observed Adverse Effect Level was 500 mg/kg/day in non-fasted dogs, while for fasted dogs it was 40 mg EGCG/kg bw per day. It should be noted that the 40 mg EGCG/kg/day did produce plasma concentrations comparable to those seen in humans administered an oral dose of 800 mg. (Isbrucker, et al 2006)
For a 22 lbs dog this equates to 400 mg of EGCG per day.
On the human side, the European Food Safety Authority published their Scientific Review of Green Tea in 2018. The panel believes that the risks associated with Green Tea come from the Epigallocatechin gallate content.
The research they reviewed leads them to believe that 800mg of EGCG per day as a supplement increases the risk of liver damage. In the study on dogs, the Epigallocatechin gallate (EGCG) accounted for 56-72% of the green tea extract given each day.
In another systemic review, also published in 2018, the researchers concluded that a safe intake limit of 338 mg EGCG/day (in a fed or fasted condition) delivered in solid dosage form and 704 mg/day for an EGCG equivalent dose (fed or fasted) might be considered for a green tea preparation consumed in beverage form.
Epigallocatechin Gallate Content
The USDA database lists the Epigallocatechin gallate content of Green tea brewed to be 70.2 mg per 100 grams(~165 mg per cup) or for Green Tea Leaves dry 7116 mg per 100 grams.
There is also research demonstrating the difference between young and old tea leaves.
- Higher in Old Tea Leaves
- Higher in Young Tea Leaves
- epigallocatechin gallate,
- epicatechin gallate,
- epiafzelechin gallate,
- glucogallic acid,
- galloylquinic acid,
- gallocatechin gallate,
Green Tea in Dog Foods
Oftentimes when Green Tea is included in dog foods it is often in minuscule amounts. Most of the time however it is included as an extract, meaning it is concentrated.
Most of the time we are highly critical when a “superfood” is included because it is almost always included in an amount where it is basically not really there.
While the reason for Green Teas’s inclusion is probably party due to marketing. There is another reason as to why it is included in small amounts, and I wouldn’t judge the formulator too harshly for it, as they were likely told to include it by the marketing department.
Based on where green tea is often found on the label below most of the vitamins and any probiotics it is probably safe to assume that it is generally included at levels well below 1%, and probably even well below .25%.
One company did list how much Green Tea Extract was in the food and it was 100 mg per kilogram or .01%.
When formulating a food for widespread distribution there are certain assumptions you have to make. The first is that a possibly large portion of pet parents do not rotate their dogs food. They either feed the same food for months sometimes years without once rotating. Secondly, even when owners do rotate it is oftentimes within the same brand. The issue with this is if it is the same brand there is probably green tea or green tea extract included in all or most of their formulas.
This being the case it would be foolish of them to include significant amounts when not much is known about chronic exposure at lower amounts. Due to the demonstrated risks, it’s best to err on the side of caution and keep the amount included lower.
A complicating factor in green tea and green tea extract inclusion in dog foods is the fact that you have to account for the fact that owners might decide to also give green tea, not knowing or adjusting the amount of green tea, based on its inclusion in the food. Moreover, many pet Parents also give supplements some of which also include green tea. So the formulator has to account for those variables when deciding how much green tea extract is included.
Now I don’t know if the person who actually formulated these foods took this into account, all I can say is that they are things I would take into account when including green tea extract in the food, because given the risks it would be irresponsible not to account for the above factors.
The companies could include green tea in higher amounts and add a warning not to give additional green tea, but we all know there are people out there that don’t read warning labels or would simply ignore the warning.
If you are feeding a food with green tea, it is important for the health and well being of your dog for you to reach out to the manufacturer of both the food you feed and any supplement’s and ask them how much green tea or green tea extract is actually in the food or supplement. So you can make any necessary adjustments. If they can also tell you the percent of ECGC even better.
Calculating EGCG content in Dog Food
We can probably safely assume that the amount of Green Tea extract is less than .5%. This equates to 5 grams per Kg of Dog Food. The actual content is likely much lower. Next, if we assume that the EGCG content is 72% (on the safe side) that is 3600 mg per KG of Food. Now all you have to do is divide that amount by how many days 1 Kg of Food lasts you. Generally, one cup of food is around 100-120 Grams. So, between 8 and 10 cups per Kg. Next you divide the 3600 mg by how many days 1 Kg of food lasts and that gives you how much EGCG they recieve from the food each day.
At the end of the day, there is still much more we need to know about the safety of green tea for our dogs and cats. While it does have many potential benefits, it does carry with it some risks especially when given in larger doses.
I would highly advise against giving the extract considering how easy it would be to give them too much as you are dealing with very small amounts and there is high variability in the EGCG content. If you do decide to give Green Tea it should be decaf and it should also not be given on an empty stomach. I would also recommend staying well below the NOAEL of 500 mg of EGCG per kg bw per day. This is relatively easy to do when giving brewed tea as it is around 165 mg per cup.
We would also advise against giving it every day until more is truly known about the long-term effects at lower doses over the course of more than 13 weeks.
Green tea does not have to be something you give every day either. Your dog or cat can still get the potential benefits without having to give it on a consistent basis.
The reason this information is so imporant to know is there are people whose dogs won’t drink or eat their food with brewed tea and they will either give a powdered form or add the leaves themselves, and when this is done there are risks.
EFSA ANS Panel (EFSA Panel on Food Additives and Nutrient Sources added to Food), Younes, M, Aggett, P, Aguilar, F, Crebelli, R, Dusemund, B, Filipi?, M, Frutos, MJ, Galtier, P, Gott, D, Gundert-Remy, U, Lambré, C, Leblanc, J-C, Lillegaard, IT, Moldeus, P, Mortensen, A, Oskarsson, A, Stankovic, I, Waalkens-Berendsen, I, Woutersen, RA, Andrade, RJ, Fortes, C, Mosesso, P, Restani, P, Arcella, D, Pizzo, F, Smeraldi, C and Wright, M, 2018. Scientific Opinion on the safety of green tea catechins. EFSA Journal 2018;16(4):5239, 89 pp. https://doi.org/10.2903/j.efsa.2018.5239
Hu, J., Webster, D., Cao, J., & Shao, A. (2018). The safety of green tea and green tea extract consumption in adults – Results of a systematic review. Regulatory toxicology and pharmacology : RTP, 95, 412–433. https://doi.org/10.1016/j.yrtph.2018.03.019
Isbrucker, R. A., Edwards, J. A., Wolz, E., Davidovich, A., & Bausch, J. (2006). Safety studies on epigallocatechin gallate (EGCG) preparations. Part 2: dermal, acute and short-term toxicity studies. Food and chemical toxicology : an international journal published for the British Industrial Biological Research Association, 44(5), 636–650. https://doi.org/10.1016/j.fct.2005.11.003
Kapetanovic, I. M., Crowell, J. A., Krishnaraj, R., Zakharov, A., Lindeblad, M., & Lyubimov, A. (2009). Exposure and toxicity of green tea polyphenols in fasted and non-fasted dogs. Toxicology, 260(1-3), 28–36. https://doi.org/10.1016/j.tox.2009.03.007
Liu, Zhibin & Bruins, Marieke & de Bruijn, Wouter & Vincken, Jean-Paul. (2019). A comparison of the phenolic composition of old and young tea leaves reveals a decrease in flavanols and phenolic acids and an increase in flavonols upon tea leaf maturation. Journal of Food Composition and Analysis. 86. 103385. 10.1016/j.jfca.2019.103385.
Rahman, S.U., Huang, Y., Zhu, L. et al. Tea polyphenols attenuate liver inflammation by modulating obesity-related genes and down-regulating COX-2 and iNOS expression in high fat-fed dogs. BMC Vet Res 16, 234 (2020). https://doi.org/10.1186/s12917-020-02448-7