Many people think that overnight tea can't be drunk, and there are many opinions. Among them, the more "alarmist" one is that drinking overnight tea will cause cancer. In fact, this statement has no scientific basis.

◆ The concept of overnight tea is difficult to distinguish.

Tea made in the morning is very common in the afternoon.

Tea brewed at work late at night will not change more than during the day after getting up early in the morning. If anything, the temperature is high during the day, and the tea leaves may change greatly.

◆ What will happen if the tea leaves are kept for a long time?

The research shows that the main change is that tea polyphenols are further oxidized and the color is deepened. A cup of clear green tea, especially at high temperature for a long time, will lose its green color and increase its yellow color. This is the yellow-red and reddish-brown oxidation products formed by the oxidation of tea polyphenols in tea, mainly theaflavins, thearubigins, theabrownins and so on. These products are non-toxic and will not cause harm to human body.

◆ Some people speculate that tea will produce carcinogenic nitrosamines overnight.

First of all, it must be affirmed that even nitrosamines in tea are negligible. Many foods we eat every day, such as bread, vegetables, pickles, salted fish, bacon, etc., all contain nitrosamines, and the content is much higher than that in tea. But I haven't seen anyone who doesn't eat. The content of nitrosamines in each kilogram of meat products is 4 ~ 50 micrograms. Isn't it terrible? Actually, it is not, because the human body itself has the function of decomposing nitrosamines.

Moreover, nitrosamines can cause cancer only when absorbed per kilogram of body weight 100 ~ 2000 mg, and they are taken in large quantities all year round. Generally, normal food intake will not cause such great harm, and the amount of tea is even more insignificant compared with food intake. If people easily "bow their heads" to these trace amounts of nitrosamines, how can they be called "the spirit of everything"?

So it is unreasonable to worry that drinking tea will bring nitrosamines harm to cancer.

In addition, studies show that tea is rich in tea polyphenols and vitamin C, which is a natural inhibitor of nitrosamines. Therefore, drinking tea can also eliminate the harm caused by other foods containing nitrosamines. Tea is rich in tea polyphenols, which can inhibit lipid peroxidation by scavenging carcinogens such as oxygen free radicals. Vitamins C and E in tea also have an auxiliary anti-cancer effect.

Therefore, overnight tea or tea that has been brewed for too long is not toxic as long as it has not deteriorated.