# Identification of Factors Influencing Fluoride Content in Tea Infusions: A Systematic Review
## 4 Discussion
This pattern is likely linked to the maturity of the tea leaves utilized; older leaves, commonly used for black and green teas, accumulate fluoride over time due to prolonged environmental exposure. Moreover, the regional origin of the tea plants strongly influenced fluoride accumulation, as areas with acidic soils and high environmental fluoride levels contributed to higher internal fluoride content [22; 53; 58]. Interestingly, some studies, such as that by [PERSON] et al. [58], found green tea to release more fluoride than black tea, suggesting that local agricultural practices and specific cultivars could shift the typical trend. In contrast, white, pu-erh, and herbal teas consistently demonstrated lower fluoride levels. Herbal teas, in particular, released minimal fluoride, confirming that non-_Camellia sinensis_ infusions are generally a safer choice for individuals needing to limit fluoride intake [19; 31; 49; 57]. Nonetheless, variability among tea types also reflects different processing techniques; for instance, extensive fermentation processes, typical for pu-erh teas, may alter fluoride availability [19; 66]. Overall, tea type remains a crucial, but not sole, predictor of fluoride content in the infusion. The form of tea and degree of leaf fragmentation significantly influenced fluoride release. Fragmented tea, such as powders and tea bags, consistently yielded higher fluoride concentrations than loose-leaf teas [19; 28; 31; 32; 49; 50; 51; 52; 54; 58; 63]. The greater surface area provided by fragmented tea particles facilitates more efficient ion extraction into the water. Studies by [PERSON] et al. [28] and [PERSON] et al. [31] directly confirmed that tea bags and instant tea products released substantially higher fluoride concentrations compared to whole-leaf forms. Additionally, industrial processing methods, including mechanical pressing and cutting of leaves during tea bag production, contribute to increased cellular disruption and subsequent fluoride liberation. [PERSON] et al. [50] highlighted that granulated teas contained fluoride concentrations comparable to or exceeding those of bagged teas, emphasizing the role of mechanical processing. These findings are critical from a public health perspective, as tea bags and powdered teas are often preferred for their convenience, potentially exposing frequent consumers to higher fluoride levels unknowingly. Thus, the form of tea preparation must be considered when assessing individual fluoride intake from tea beverages. Brewing conditions--particularly time, temperature, and water composition--further modulated fluoride release. A robust relationship was observed between longer brewing times and increased fluoride extraction [19; 31; 32; 51; 52; 54; 56; 61; 63; 64; 68]. [PERSON] et al. [61] and others showed that fluoride concentrations rose steeply during the first 20 min of brewing, after which the rate of release plateaued. This suggests that most available fluoride is solubilized early in the brewing process, and prolonged brewing does not proportionally increase fluoride concentrations. Similarly, higher water temperatures enhanced fluoride extraction due to increased solubility and diffusion rates [51; 54; 68]. Beyond brewing parameters, the chemical composition of the brewing water played a vital role. Studies revealed that using water with higher baseline fluoride levels led to increased fluoride content in the resulting tea infusion [22; 63; 65]. However, [PERSON] et al. [54] observed that in water with extremely high fluoride content, tea leaves could absorb part of the fluoride, thus slightly reducing the infusion's fluoride concentration compared to the original water. Moreover, water hardness negatively correlated with fluoride extraction: higher concentrations of calcium carbonate precipitated fluoride ions, thereby lowering their availability in the infusion [32; 48]. These findings emphasize that not only tea characteristics but also water quality must be accounted for in fluoride exposure assessments.