# Identification of Factors Influencing Fluoride Content in Tea Infusions: A Systematic Review
## 1 Introduction
Finally, it should be noted that a person's fluoride intake from tea infusions is influenced by the concentration of fluoride in the water and by factors related to the preparation of the infusion, which affect the amount of fluoride released from the leaves [13,22,23] (see Figure 1). The release of fluoride from tea is influenced by a multitude of factors. These factors are diverse and related to the plant itself, including its growing environment, brewing circumstances and parameters, the form of the tea, and the technique of processing the leaves and the addition of various spices. The age of the plant itself has been demonstrated to affect the fluoride concentration. Consequently, as the plant matures, the fluoride concentration increases. This assertion is corroborated by studies undertaken by [PERSON] et al., which demonstrated a higher fluoride content in older tea leaves [21]. A closer examination of the plant itself, the soil type, or more precisely, the pH level, is clear in our considerations. It has been demonstrated that elevated levels of fluoride in the foliage are associated with acidic soil [23; 24]. Consequently, the level of fluoride will be elevated. The bioavailability of ions, such as fluorine and aluminum, in soil is subject to variation and correlation with its acidity. At a pH of 5.5, aluminum ions in conjunction with fluorine ions form a stable Al-F complex, which is efficiently absorbed by tea plants [25]. The region of cultivation from which tea comes also affects the fluoride concentration [26]. The form of tea has been demonstrated to influence the quantity of fluoride released. Specifically, tea bags have been found to release a higher concentration of fluoride compared to loose-leaf tea varieties during the infusion process. This phenomenon can be attributed to the utilization of older leaves in the production of tea bags [27]. A similar trend was observed in the study by [PERSON] et al., where it was found that the use of mature leaves resulted in a higher fluoride release during the pressing process [27]. In this instance, too, older leaves are utilized, resulting in these teas exhibiting a higher fluoride concentration [24; 28]. The fluoride concentration is observed to vary depending on the type of tea. It is black tea in the infusion that--as a rule--contains the highest concentration of this element [19]. In descending order, green tea, Earl Grey, pu-erh, and white tea follow. Fluoride is present in trace amounts in herbal teas. Brick tea, as previously referenced, has been observed to contain elevated levels of fluoride, while white tea, in comparison to black, green, and oolong varieties, has been found to exhibit reduced levels [29]. Numerous studies have indicated a direct proportionality between brewing time and the fluoride concentration in the infusion. The concentration of fluoride in the infusion increases in proportion to the duration of the infusion process [30]. Furthermore, the repeated infusion of the same quantity of tea has been shown to increase the fluoride content [31]. Conversely, the infusion resulting from a single, continuous infusion contains a lower amount of fluoride. It has been demonstrated that multiple infusions of the same quantity of tea result in an increase in the amount of fluoride released. Of particular interest is the observation that the initial infusion of a given quantity of tea releases the greatest amount of fluoride. The extraction of fluoride ions into the infusion is influenced by the temperature of the water used for preparation, with boiling water being the standard [32]. The total fluoride content will also be influenced by the quality of the water itself. Endemic water may contain higher or lower concentrations of fluoride ions. Furthermore, it is imperative to acknowledge the significance of water treatment within the water supply network. Groundwater intakes are distinguished by their varying fluorine content [33].