1. First, let's look at: The relationship between fluoride and human health

Fluoride is an element widely found in the earth's crust and is essential for humans within a certain range. An appropriate amount of fluoride can prevent vascular calcification. Fluoride deficiency often leads to rickets, osteoporosis, and dental caries. Generally, the recommended fluoride intake is about 3-5 mg per day for adults and 1-2 mg per day for children. Excessive fluoride intake can also cause fluoride poisoning.

Drinking tea can supplement fluoride in small amounts, which is beneficial to the human body, especially for strengthening teeth and preventing cavities. However, due to excessive tea drinking, there have been continuous reports in recent years of tea-drinking type fluoride poisoning in ethnic minority areas, with clinical manifestations mainly including dental fluorosis, skeletal fluorosis, and increased urinary fluoride.

2. The source of fluoride in tea leaves

Regarding the source of fluoride, the fluoride content in tea has an insignificant relationship with the background of chemical elements in the soil but is closely related to the micro-ecological environment and atmospheric environmental quality of the tea garden. Fluorides can enter the tea plant through stomata or water pores, move along the导管 to the leaf tips and edges, gradually accumulate, and react with calcium in the leaf tissues to form insoluble fluorides, which precipitate locally, resulting in higher fluoride content in tea leaves. If fluoride-containing phosphorus is applied in tea gardens, the fluoride content in tea can increase. Increasing phosphate fertilizer application increases the fluoride content in tea along with the amount of fertilizer applied. The processing process generally does not easily cause an increase in fluoride content, and the fluoride content in finished tea is directly related to the selection of raw materials.

3. The fluoride content in tea leaves

Fluoride content in different parts of the tea plant

The fluoride content varies greatly among different parts of the tea plant. Tea leaves (especially old leaves) are the main accumulation organ for fluoride, with the fluoride accumulation in all leaves accounting for 98.1% of the total fluoride accumulation in the whole plant. The difference in fluoride content between different parts of the tea plant is very large, especially between old leaves and young leaves, which can be 12 to 36 times. The fluoride content in tea stems is low. The fluoride content in newly sprouted tea shoots is low, and even undetectable in newly sprouted one-bud-two-leaf shoots. However, after growing for another 20 days, the fluoride content in the young leaves can reach 249 mg/kg. Old leaves are about twice as high as young leaves, and the average fluoride content in old tea stems can also reach 151-100 mg/kg, which is 38 times higher than that in young tea stems. This shows that the fluoride content in tea stems and leaves increases with the degree of aging. Usually, the tea we drink is made from young leaves, which have low fluoride content and generally do not cause fluoride poisoning.

Additionally, can drinking Huangpian tea cause fluoride overdose? Many people question whether Huangpian is old leaves with high fluoride content that is harmful to health when consumed. In fact, the formation of Huangpian is, first, the third leaf outside the one-bud-one-leaf or one-bud-two-leaf picked during harvesting, generally not reaching the fourth leaf; second, during rolling, if not rolled sufficiently, the strips are looser. Under these two circumstances, kill-green can cause the leaves to turn yellow or a darker green. If this part of the tea is not sorted out, the appearance of the compressed strips will be poor. Therefore, Huangpian is not strictly old leaves. The fluoride poisoning among tea farmers in ethnic minority areas is actually due to their excessive consumption of old leaves, not the Pu-erh tea we usually drink.

4. About the leaching rate of fluoride

Studying the leaching of fluoride from tea is of great significance for accurately analyzing and measuring the fluoride content in tea. Experiments have found that the brewing time has a great relationship with the dissolution of fluoride from tea. Most of the fluoride in tea is dissolved after brewing for 5 minutes. The amount of fluoride leached after brewing for 20 minutes accounts for 55.3% to 97.7% of the fluoride content after soaking for 24 hours. Different types of tea have different leaching rates.

The smaller the ratio of tea to brewing water, the lower the fluoride leaching rate from tea, and vice versa, the higher the fluoride leaching rate. After soaking tea at 80°C and 100°C water temperature for the same time, the water-leached fluoride content in the tea water does not change much; the amount of fluoride leached from tea is roughly proportional to the brewing time; the amount of fluoride leached from tea decreases with the increase in the number of brews; for the number of brews, the fluoride leached in the first 3 infusions accounts for most of the total fluoride leached.

5. How to drink tea daily (taking Pu-erh tea as an example)

Pu-erh tea has a relatively high fluoride content among all tea types. Data suggests that each person should not drink more than 11g of Pu-erh tea per day. For example, if you drink tea alone, with each serving being 5-6g, and each tea is brewed for 15-20 infusions, then you should not exceed two types of tea per day. If drinking with others (e.g., 3 people), with each serving being 6-8g, and each tea is brewed for 15-20 infusions, then you should not exceed 4-5 types of tea per day, and so on. This is roughly the idea.

At the same time, it is recommended that when drinking tea, the first and second infusions should be used only for rinsing the tea and not consumed, which can significantly reduce human intake of fluoride and prevent fluoride poisoning. Additionally, it is better to brew and drink tea simultaneously, rather than using a large cup for long-term stewing.

In summary, "fluoride is a double-edged sword." An appropriate intake of fluoride is beneficial to the body. Currently, there is no unified international standard for the safe daily fluoride intake per person. The US recommended standard is that the upper limit of total daily fluoride intake for children is 2.5 mg, and the total daily fluoride intake for adults is 1.5-4.0 mg. Therefore, regular tea drinkers should avoid using fluoride toothpaste. Based on the above standards, the amount of fluoride in tea, and its leaching rate, we can adjust the amount of tea we drink appropriately according to our body's needs.