According to the media, researchers at the University of Derby in the U.K. measured the amount of fluoride in tea and found that "value brand" teas sold in supermarkets detected levels of fluoride that could be harmful to health if consumed in large amounts.
Fluoride is a necessary nutrient for the human body, but excessive intake can cause joint pain, muscle weakness, osteoporosis, and kidney damage.
Laura Chan, who was involved in the study, explains why high levels of fluoride were found in Value brand teas.
As the tea plant grows, it accumulates fluoride from the soil, but it is the mature tea leaves that accumulate the most fluoride.
When tea leaves are harvested, the mature leaves are used to produce lower quality teas, such as the virtuous tea bags.
In contrast, the tender leaves on the shoots and tops of the tea plants (which have not yet accumulated fluoride) are used to make high-quality specialty tea products.
This is why lower-priced teas contain more fluoride, according to the study.
The study found an average of 6 milligrams of fluoride per liter of tea from inexpensive tea bags. In the U.K., there is no maximum acceptable daily intake of fluoride, while in the U.S. it is limited to 4 milligrams per day. If tea is made from inexpensive tea bags, drinking about four cups of tea a day would exceed this limit. The study also found that drinking inexpensive teas on an empty stomach, especially first thing in the morning, can have a greater impact on health.
The study was based on inexpensive value brand tea bags sold in the UK. However, Japan's tea self-sufficiency rate is almost 0%. In other words, almost all tea is imported from overseas. Perhaps the situation in Japan is the same as in the UK.