Many people have the habit of rinsing tea when drinking tea, believing that the second brew tastes best. Experiments have found that most fluoride ions in tea leaves are leached out during the first brewing, the fluoride content in the second brew decreases significantly, and by the third brew, the fluoride content is similar to that of plain water.

If you need to increase fluoride intake, you should drink more of the first brew; residents in high-fluoride areas can drink the second or third brew to avoid excessive fluoride intake. However, similar to the loss of fluoride, valuable trace elements such as Mg, Zn, Ca, Fe, and Mn also decrease sharply with each brew, so it is not recommended for high-fluoride areas to brew tea leaves multiple times before drinking.

In addition to the number of brews, Dr. Li's research also provides reference answers regarding the length of brewing time. The longer the tea is brewed, the higher the fluoride content in the tea soup. The fluoride content measured in tea brewed for 15 minutes accounts for the majority of the leachable water-soluble fluoride. After 15 minutes, the leaching rate of fluoride from the tea leaves slows down, and the temperature of the tea drops rapidly. Therefore, if you are using tea to increase fluoride intake, it is recommended to brew for 15 minutes.

The situation varies for different types of tea. If you are drinking kuding tea, you don't need to wait that long, as most of its fluoride is released within the first minute of brewing. This shows that multiple brews cause a significant loss of trace elements like fluoride in tea leaves. From a health perspective, it is better to drink the first brew.