Green Tea and Kidney Stones

Short Introductory Video

What are kidney stones?

Kidney stones also called renal calculi, urolithiasis or nephrolithiasis, are relatively small masses of crystallised urine components that accumulate in the kidneys under certain circumstances.

There are four types of kidney stones; calcium oxalate (the most common according to NYU Health), uric acid, struvite (a compound of magnesium, ammonia and phosphate), and cystine (an amino-acid derived from protein). 

Kidney stones tend to form where the urine is most concentrated, such as in the collecting ducts of the kidney, but can occur throughout your urinary tract.

Various studies have claimed that green tea can facilitate the excretion of kidney stones due to the presence of beneficial compounds such as polyphenols and antioxidants. However, more research is needed to validate the results.

Image Credit by CC BY-SA 4.0, Link

Causes and risk factors of kidney stones

According to the National Kidney Foundation, the risk of kidney stones is about 11% in men and 9% in women. 

Kidney stones have a variety of causes and risk factors, including: 

• Diet: Oxalate-rich foods can increase risk e.g. beets, chocolate, spinach, rhubarb, black tea, and nuts. Very high doses of vitamin C or D can slightly increase stone formation. A diet rich in animal protein or fructose may also cause stones to form.
• Insufficient hydration
• Family/personal history of kidney stones
• Medical conditions e.g. high blood pressure, diabetes
• Obesity
• Recurrent urinary tract infections
• Certain supplements and medications: Aspirin, antacids, diuretics (used to reduce fluid build-up, e.g. furosemide), certain antibiotics, certain antiretroviral medicines (used to treat HIV) and certain anti-epileptic medicines. High dose vitamin C or D supplements (more than 500mg/day).

Symptoms

Sometimes, tiny stones move out of the body in the urine without causing too much pain, requiring only that you take painkillers and drink plenty of water.

Only when the stones grow larger and lodge in the ureter (the tube that takes urine from the kidneys to the bladder) do symptoms tend to be severe. This is because urine builds up behind the blockage and causes the ureter to spasm and the kidneys to distend, resulting in severe pain.

The symptoms of kidney stones include:

• A severe, stabbing pain in the side and back on the affected side that:
  • radiates to the lower abdomen (tummy) and groin
  • comes in waves and fluctuates in severity
• Pain or burning sensation while urinating
• Pink, red or brown urine
• Cloudy or foul-smelling urine
• A persistent need to urinate, urinating more often than usual, or urinating in small amounts
• Nausea and vomiting
• Possible infection and fever

In some circumstances, larger stones may necessitate surgery, or a procedure called extracorporeal shock wave lithotripsy (ESWL), where the stone is broken up with concentrated sound waves to allow it to pass down the ureter to the bladder.

Preventing kidney stones

The following steps can help you to prevent kidney stones:

• Stay hydrated with water or citrus juices
• Eat more calcium-rich foods - there is a common misconception that you should cut back on calcium when you have kidney stones. Advice on diet and kidney stones can be found here.
• Eat less sodium-rich foods - high sodium elevates urine calcium concentrations and can encourage stone formation.
• Eat fewer oxalate-rich foods
• Eat less animal protein - protein acidifies the urine and encourages oxalate and uric acid stone formation.
• Avoid vitamin C supplements
• Talk to your doctor about preventative medications

Green tea and kidney stones

Image credit by CC BY-SA 4.0, Link

Green tea is made from the leaves and buds of the tea plant Camellia sinensis, which have not undergone the withering and oxidation process used to make black tea. Infused green tea is largely devoid of nutrients, containing 99.9% water.

Various health claims have been made for the antioxidant phytochemicals, polyphenols, and catechins contained within it. However, to date, these health claims remain controversial, but state that green tea:

• Contains beneficial bioactive compounds, such as polyphenols, which have anti-inflammatory and antioxidant properties and catechins, such as epigallocatechin-3-gallate (EGCG), which are also antioxidants. They reduce the formation of free radicals in the body and may protect the cells against oxidative damage.
• May help prevent several chronic diseases such as diabetes and some cancers, such as prostate or colorectal cancer. A (weak) Japanese study found that those who drank more than 6 cups/day of  green tea had an approximately 42% lower risk of type 2 diabetes.⁽⁶⁾
• Lowers blood pressure, total cholesterol and levels of LDL (bad) cholesterol in the blood, according to Hartley et al (2013). This may contribute to lowering the risk of cardiovascular disease.⁽⁵⁾⁽⁸⁾

In 2006, it was reported by Jeong et al that the catechin EGCG protected kidney cells against oxalate toxicity, and the EGCG in green tea reduced oxalate crystal formation and increased oxalate excretion in rats, effectively reducing the risk of stones.

Chen et al (2010) showed that the constituents of concentrated green tea extract altered the crystallisation of calcium oxalate and made the crystals flatter and less likely to form large, stable kidney stones. Smaller stones are more likely to pass through the body without symptoms than larger ones.  

More recently, Barghouthy et al (2021a) reviewed the evidence from several methodologically strong studies and concluded that drinking tea, and in particular green tea, had a protective effect against kidney stone formation.

Moreover, the diuretic effect of the caffeine in tea (and coffee) increased the excretion of sodium, potassium, and calcium, all of which are key components of kidney stones.

In addition, green and herbal teas have a lower oxalate content than black tea, thus further protecting from kidney stones.⁽²⁾

However, according to New Scientist magazine, green tea polyphenols can cause kidney and liver damage if taken in large quantities, and this is especially true of concentrated green tea supplements, so there are risks as well as benefits. Nonetheless, drinking up to 6-8 cups a day of regular green tea should be fine and beneficial.^(9,10)

FAQs

Is green tea bad for your kidneys?

Green tea is good for you, but only when drunk in moderation. It might be wise to avoid concentrated green tea pills as these might damage the liver and kidneys.

Does green tea help prevent kidney stones?

There is some evidence that drinking green tea helps prevent or reduce kidney stone formation, and may limit the size of stones that do form, making them easier to pass in urine.

What kind of tea is bad for kidney stones?

Black tea is rich in oxalate, a cell toxin and one of the components of the most common types of kidney stones. Drinking too much of this beverage may cause kidney stones to form.

Does green tea aggravate kidney stones?

There is evidence that green tea does not increase the risk or formation of kidney stones.

What can I drink to urinate a kidney stone out?

Drink plenty of water. Limiting dietary sodium will help limit the size of the kidney stones, making them easier to flush out. Good hydration reduces kidney stone risk but also helps you to flush out small stones that do form. Other natural remedies which may help include lemon juice, basil juice, pomegranate juice, and apple cider vinegar.

Is honey OK for kidney stones?

This is controversial. However, there is some thinking that honey and lemon juice may be beneficial to the kidneys and prevent stone formation. Moderation is the key here.

Which foods are bad for kidney stones?

Avoid foods rich in sodium, oxalate, animal protein, high-fructose corn syrup, and reduce alcohol. Also, avoid high-dose calcium and vitamin C and D supplements.