There are many people, they all have the habit of drinking water in the morning, most of them are cold white or tea left last night. Some people are entangled, I heard that overnight water and overnight tea have excessive toxic metals, which are easy to cause cancer, and they are not safe to drink.
01
Overnight tea, overnight water,
How "poisonous" is the whole process?
"Overnight tea and overnight water cannot be drunk, nitrites, heavy metals, and bacteria are all over the standard!" Speaking of overnight tea and overnight water, many people shy away, I don't know where I heard about it, anyway, I decided that overnight tea and overnight water cannot be drunk.
What are the facts? The Food Testing Center of Yinzhou District, Ningbo City, Zhejiang Province conducted a test and discussion on this.
Experiment 1: Overnight water
First of all, prepare household boiling water containers of different materials, including stainless steel electric kettles, iron kettles, aluminum kettles, and induction cooker coated pots.
Then, add an appropriate amount of water to the container, keep boiling for different times after boiling, and then pour into a beaker and a sterile sampler to cool naturally. After 0 hours, 24 hours, and 48 hours, nitrites, heavy metals and bacterial indexes were detected in the water.
Source: Broadcast Xuzhou
The experimental results showed:
(1) Nitrite: The nitrite in the thousands of boiling water and overnight water does not exceed the safety limit, and the longer the boiling time of the water, the higher the content of nitrite. In addition, the longer the water is left after cooling, the higher the nitrite content.
(2) Heavy metals: The heavy metals in the stainless steel electric kettle, iron kettle and induction cooker coating pot have not exceeded the standard, and the heavy metals in the aluminum kettle have seriously exceeded the standard. With the extension of the boiling time, the heavy metals in the water boiled with electric kettles and induction cooker coated pots do not change much, the iron content in the water boiled with iron kettles increases, and the aluminum content in the water boiled with aluminum pots increases significantly.
In addition, after boiling water, pour it out and leave it for about 24 hours, and the content of heavy metals does not change much. However, if the water in the iron kettle is not poured out, the iron content will increase significantly.
(3) Bacterial content: No matter what kind of material of water is used to boil, the water is poured out and placed for 24 hours, 48 hours or even 72 hours after boiling, and the total number of colonies has not been detected, indicating that after the water is boiled, the microorganisms have basically been killed, and there are very few cases where bacteria exceed the standard.
Experiment 2: Overnight tea
Prepare equal amounts of black tea, green tea and fermented tea Pu'er tea respectively, then prepare nitrite standard curve, and then precipitate and filter the tea for comparison.
The experimental results showed:
No nitrite was detected in freshly brewed tea, the nitrite content in tea left for 8 hours was a little higher than the detection limit, and the nitrite content in tea left for 24 hours was lower than the detection limit.
Among them, the maximum nitrite content of tea is 2.95mg/l, which is far lower than the toxic dose.
Some people say: overnight tea contains secondary amines, which can be converted into nitrosamines and have a carcinogenic risk. In fact, secondary amines are widely present in food, and the amount of secondary amines we consume from staple foods every day has far exceeded the amount consumed by drinking overnight tea.
Moreover, secondary amines are not carcinogens, and they will react with nitrates to form nitrosamines under the conditions of suitable pH, temperature and number of microorganisms, so do not worry.
Although experiments have proved that overnight water and overnight tea are not very harmful to the body, it is still necessary to pay attention to:
1. Do not boil too much water at one time, drink as much as you want, and the water that has been left for no more than 24 hours can be boiled again for drinking, but if it exceeds 24 hours, it is best to throw it out.
2. Try not to boil water with an iron kettle, the iron kettle is easy to rust, boiled water placed in the iron kettle for a long time, will cause iron elements to exceed the standard, and will cause gastrointestinal discomfort after drinking.
3. Try not to boil water with an aluminum pot, which may cause the aluminum element in the water to exceed the standard.
02
The water that really can't be drunk is this
It can be seen that overnight water and overnight tea are generally drinkable as long as they are not left for too long. The water that you really can't drink is scalding water.
Blanched water, refers to water with a temperature of more than 65°C, and the WHO classifies hot drinks above 65°C as a Class 2A carcinogen, and regular consumption increases the risk of esophageal cancer.
Our esophageal mucosa is very delicate, can not withstand hot drinks above 65 ° C, often drink hot water, hot tea, etc., esophageal mucosa will be repeatedly damaged, stimulate cell cancer, may induce esophageal cancer.
Surveys show that residents in Asia, South America and East Africa, where esophageal cancer is high, generally have the habit of drinking hot drinks and eating hot food. In countries with low esophageal cancer rates such as Europe and North America, the temperature at which residents drink tea and coffee will basically not exceed 60 °C.
For Chinese who "eat rice while it is hot, tea should be drunk hot", the incidence of digestive tract tumors such as esophageal cancer is significantly higher than that of Westerners, especially in Fujian and Guangdong regions of China, which is related to local residents' likes to drink kung fu tea, eat casserole porridge and other hot foods.
Extension: Correct drinking posture
Drinking water is also exquisite, but in fact, it is not so complicated, the correct drinking posture, should be like this:
1. Replenish water in time, do not wait for thirst to drink water, an adult's daily water intake should be about 1500ml-1700ml.
2. The time to drink water is not divided into morning and evening, and there is no specific time interval, and it is important not to drink water for a long time.
3. Before going to bed, you can moderately replenish water, drink about 100ml-200ml of water, and relieve the symptoms of sleep dehydration.
4. Water should be drunk in moderation, do not drink too much, when the total amount of water ingested by the human body far exceeds the amount of drainage, it will lead to hyponatremia.
Water is the source of life, we must drink water well, drink water scientifically, and replenish water in time to maintain good health. After reading this article, do you know the correct posture for drinking water?
Source: 39Health.com
Editor: Chen Jiashuang Responsible editor: Yue Hongli
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