Is Tea the culprit for yellowing teeth? Does overnight tea cause cancer? Is Green Tea too harsh on the stomach?

Such assertions might have become “common sense” in your mind, but today, Old Bamboo will tell you: these unfair accusations don't apply to tea.

01

Does Tea Cause Yellow Teeth?

Tea leaves stains on the cup, leading some to speculate: could yellowing teeth be due to tea leaving stains on them as well?

The yellowing of teeth is primarily caused by the state of the teeth themselves and external factors, one of which is indeed “consumption of food and drinks that easily stain.”

So here's the question: is tea a substance that easily stains?

In tea, the substances responsible for coloring are called tea pigments, which are derived from the transformation of polyphenols in tea. When Drinking Tea, polyphenols adhere to the teeth, causing them to turn yellow. However, tea pigments are not as difficult to remove as regular pigments. The degree of staining they cause can be cleaned away with daily brushing.

At the same time, drinking tea is beneficial for the teeth. The polyphenols and fluoride in tea can strengthen gums and inhibit bacterial growth. That's why many toothpastes contain tea polyphenols to protect and whiten teeth.

TRUTH If you brush your teeth, tea does more good than harm; if you don't brush your teeth… even without drinking tea, your teeth wouldn't be white anyway, right?

02

Does Overnight Tea Cause Cancer and Shouldn't Be Drunk?

“Sardines expire, canned meat expires, even cling wrap expires,” in people's minds, the shelf life of tea is especially short, so much so that it turns from beneficial to carcinogenic after just one night.

The reasons people believe overnight tea shouldn't be drunk mainly include: 1. Tea left for too long spoils and turns sour; 2. After being left overnight, tea produces large amounts of nitrite, which can cause cancer.

CCTV conducted an experiment where tea was left for 12 and 24 hours before testing and measuring it. The conclusion was: 1. Compared to freshly brewed tea, overnight tea did not spoil in taste and remained safe to drink. 2. The nitrite content in overnight tea did not exceed safe limits and was insignificant.

On the contrary, tea can eliminate the harm caused by other foods containing nitrosamines. Tea is rich in polyphenols and vitamin C, both natural inhibitors of nitrosamines, which reduces the risk of cancer.

TRUTH As long as the tea hasn't spoiled, overnight tea is harmless to the human body. However, heating or choosing fresh tea would taste better.

03

Is Green Tea Too Harsh on the Stomach?

After drinking eighteen cups of strong green tea on an empty stomach, Person A said, “Green tea is good, but it's harsh on the stomach.” Green tea responds: …

Compared to fermented teas like black, red (oolong), and oolong tea, green tea retains more of its natural substances, making its Health benefits relatively higher. However, due to the higher content of tannins and caffeine in green tea, tannins can irritate the stomach lining, earning green tea a reputation for being harsh on the stomach.

However, the harm green tea can cause to the stomach has been seriously exaggerated. In moderation, normal consumption of tea won't burden the stomach at all. Those who experience stomach discomfort due to green tea mainly overdo it, such as drinking tea on an empty stomach, brewing tea too strong and for too long, or drinking excessive quantities of tea daily. Drinking to such extremes, the blame for stomach issues unfairly falls on green tea.

TRUTH The claim that green tea is harsh on the stomach is based on specific conditions. Drinking strong tea on an empty stomach won't harm the stomach.

04

Does Milk + Tea = Kidney Stones?

The rumor goes: oxalic acid in tea reacts with calcium in milk to form calcium oxalate, which isn't easily absorbed by the human body. Long-term consumption can lead to kidney stones. Sounds plausible?

Before being taken aback by this seemingly professional chemical formula posted on social media, let's first understand what calcium oxalate is: oxalic acid is one of the normal metabolic products in the human body. When oxalic acid meets calcium, calcium oxalate forms. Small amounts of calcium oxalate are normally filtered out by the body. Large amounts can accumulate and precipitate, leading to kidney stones.

A 200 ml cup of tea contains only about 10 mg of oxalic acid, while the normal intake of oxalic acid for humans is 185~214 mg. The contribution of tea to this amount is negligible. What's even more unjust is that the combination and precipitation of natural calcium sources (like milk) and oxalic acid actually prevents their absorption by the digestive system, reducing oxalic acid levels.

In addition to tea and milk, similar rumors exist about tea and eggs, tea and mutton, and tea and sugar. I won't go into detail about each one, but I swear by tea eggs that all of these claims are mere rumors.

TRUTH The rate of kidney stone occurrence among Britons, who love to drink milk tea, is 2% to 3%, significantly lower than the normal rate of 9% to 10%. So, what do you think?

05

Are Tannins in Tea a Terrifying Substance?

This particular rumor has a notable origin: Julia Morton, an economic botanist from the University of Miami, wrote in her article “The Dangers of Tea” that the tannins in tea can lead to the terrifying esophageal cancer.

Many took her words as gospel because of her academic title, but the fact is that the article was published in 1987 when medical science wasn't as advanced, and Julia confused the concepts of tannins and polyphenols.