# Identification of Factors Influencing Fluoride Content in Tea Infusions: A Systematic Review
## 4 Discussion  
This systematic review sought to answer the research question: What factors influence the fluoride content in tea infusions? The findings consistently demonstrate that fluoride release is not uniform but rather modulated by multiple interacting variables, including tea type, form of tea, brewing parameters, and external modifiers such as the water's properties or the addition of spices. While wide variations in fluoride concentrations were observed, common trends were identified. Black and green teas tended to release the highest amounts of fluoride, particularly when processed into bagged or powdered forms. A particular threat in the context of fluorosis risk is the consumption of economy tea, which is a blend of teas from China, Sri Lanka, and India. [PERSON] et al. [52] proved that after 2 min, the infusion contains almost twice as much fluoride as black tea, which, according to most studies, is considered the greatest source of fluoride among all types of tea. Consumption of 1 L of economy tea, which is about 4 cups, can lead to up to 150% of the daily recommended fluoride intake. This dietary exposure is further supported by systemic data. In addition to the variability in fluoride levels found in tea infusions, some studies have also explored systemic fluoride exposure resulting from high tea consumption. For example, [PERSON] et al. [70] examined fluoride levels in urine samples from more than 1700 individuals in Tibet and found that excessive intake of brick tea (up to 3.2 L/day) was associated with elevated fluoride concentrations in the body and a high prevalence of dental and skeletal fluorosis. These findings highlight the value of integrating biomarker-based assessments--such as fluoride levels in urine or blood--into future research to better evaluate the health risks linked to chronic tea consumption. Longer brewing times and higher water temperatures consistently increased fluoride release, although a plateau was often observed beyond a certain point. Moreover, the mineral composition and pH of the water used for infusion emerged as additional significant factors. These results highlight the multifactorial nature of fluoride release during tea preparation and suggest that both intrinsic properties of the tea and extrinsic brewing conditions must be considered when evaluating potential fluoride exposure from tea consumption. Some publications draw attention to the significant effect of drinking tea infusion on the concentration of fluoride in the blood [71; 72; 73; 74]. It has been proven that drinking significant amounts of brewed tea, in the amount of several cups or 30 glasses of iced tea per day, is equivalent to 13-14 mg of fluoride [71]. Such amounts lead to reaching a toxic level of fluoride in the blood, i.e., >15 umol/L, which leads to osteogenesis, pain, bone fractures, kidney disorders, and digestive system disorders [72]. It is worth mentioning that the above symptoms are influenced by the sum of fluoride from water and tea, as well as from drugs such as flucoxentine, and the accumulation of fluoride can be intensified by kidney diseases [73]. Disorders related to excessive tea consumption are usually caused by drinking habits practiced for even 30 years, and in some cases, restoring the correct level of fluoride in the plasma (0-4 umol/L) is impossible despite radical treatment lasting even more than 10 years [71; 74]. Future studies should also focus on the above issue to accurately assess  
Figure 5: Risk of bias across the included studies, assessed using the JBI checklist for quasi-experimental studies. Green indicates low risk, red indicates high risk. what amounts of tea are safe to consume in people for whom it is a significant component of the diet. Among the factors analyzed, tea type emerged as one of the most significant determinants of fluoride release. Across the majority of included studies, black teas exhibited the highest fluoride concentrations, followed closely by green teas [19; 28; 32; 47; 51; 52; 55].