If you’re overweight and regularly consume too much food and beverages high in sodium and oxalates, you run a higher risk of developing a kidney stone, especially if you don’t hydrate yourself properly.

A kidney stone is a hard deposit that forms within the urinary system of the kidney. It usually occurs when minerals, such as calcium, oxalate, uric acid, phosphate, combine and crystallise in the urine.

“Kidney stones (also known as urinary stones) are a very common condition around the world. If you have had a kidney stone, there is a 50 per cent chance of another appearing within the next five to 10 years, thus prevention is the best course of action,” advised Dr Nor Azhari Bin Mohd Zam, Senior Consultant from the Urology Centre at Singapore General Hospital (SGH), a member of the SingHealth group.

4 Ways to prevent kidney stones from forming

To reduce your risk of developing kidney stones, you should:

1. Drink sufficient water to produce light and clear urine.

Dehydration plays a very important role in kidney stone formation. While there is no particular time frame for kidney stones to form, the risk goes up if you are dehydrated, as the concentration of stone-forming minerals in the urine will be higher.

Thus, drink about 21/2 to 3 litres of water per day, or about 12 cups.

“As a rule of thumb, your urine should be quite clear at most times of the day. If the urine appears yellowish or concentrated, it means there is either low fluid intake or excessive sweating,” explained Dr Nor Azhari.

2. Consume less oxalate-rich foods.

About 80 per cent of kidney stones are made up of calcium oxalate, thus those who have a high risk of forming calcium oxalate stones should consume less oxalate-rich foods.

Oxalate-rich foods to avoid include spinach, chocolate, nuts, tea, soya products and berries, which can contribute to high levels of urinary oxalate, a stone-forming mineral.

If you find it difficult to avoid these foods, you can take calcium together with oxalate-rich foods during a meal. This would allow the calcium to bind to the oxalate so that the oxalate can be excreted.

3. Reduce salt and protein in your diet.

A reduction in dietary salt is essential to lower urinary calcium levels. Eating less animal protein also increases urinary citrate, which prevents stone formation.

Aim for a salt intake of less than 3g to 5g per day, which will help reduce urinary calcium levels.

4. Continue eating calcium-rich foods, but use caution with calcium supplements.

Diets low in calcium can also increase kidney stone formation in some people. This is because a lower calcium intake increases oxalate absorption from the gut and, consequently, increasing urinary oxalate level.

Taking of calcium supplements is not recommended if you want to reduce your risk of kidney stones. Instead, consume calcium-rich diary products that will provide you with your normal daily calcium requirement. If in doubt, please consult your doctor or a dietician.

"Prevention is important. Adequate water intake is crucial. If you tend to form kidney stones, try to drink enough liquid throughout the day to produce at least two litres of clear urine," Dr Nor Azhari said.

"Calcium intake is also important. Recent studies have shown that foods high in calcium, including dairy products, may help prevent calcium stones. Oxalate intake should be monitored, especially for those prone to forming calcium oxalate stones. Vitamin D intake and meat intake may also need to be regulated based on the type of stones formed," he added.

Symptoms of kidney stone

A kidney stone is not always symptomatic at an early stage. Pain and other symptoms of kidney stone may show up only when the stone has grown large in size and moves down the ureter, the tube that connects the kidney to the bladder.

“At this stage, the stone can cause spasms and blockage of the kidney. The pain can be so intense that the patient may roll around on the floor,” says Dr Nor Azhari.

The following symptoms can occur:

  • Loin pain: A sudden and severe pain of the back and sides below the ribs, which can radiate downwards towards the groin (also known as renal colic).

  • Blood in the urine (haematuria)

  • Frequency and urgency in urination

  • Nausea and vomiting

  • Fever and chills: If there is superimposed infection

Kidney Stone Symptoms

When is blood in urine (haematuria) dangerous and when is it not? Click here to find out

Causes and risk factors of kidney stones

Kidney stones occur when certain salts and minerals are present in excessive concentrations in the urine, and these eventually precipitate into small crystals that accumulate into stones.

There is no single definite cause for the formation of stones, but is more likely due to several contributing factors that increase the risk of stone formation, which include:

  • Age: Usually more common in older individuals ~40 – 60 years of age.

  • Obesity: Has been associated with >50% higher risk of stone formation.

  • Genetic history: A history of kidney stones within the family is associated with a higher risk.
    “Individuals with a strong family history have 2-3 times the risk of developing a kidney stone compared to those who do not,” said Dr Nor Azhari.

  • Dehydration: A lack of fluid intake leads to concentration of salts in the urine, increasing risk of stone formation.
    “The main environmental factor is living in a hot climate, where decreased fluid intake coupled with excess sweating can lead to low urine volume and an increased concentration of certain minerals in the urine,” he added.

  • Diet: Certain diets high in oxalate (nuts, long beans, chocolate), high in purines (red meat, organs, seafood).

  • Previous kidney stones: A person with a diagnosed kidney stone has a 50% risk of developing another stone within the next 10 years.

  • Certain medical conditions: Diabetes, metabolic syndrome, hyperparathyroidism, renal tubular acidosis, gastrointestinal diseases (including inflammatory bowel disease, malabsorption, bariatric surgery, previous intestinal resections).
    Known conditions associated with urinary tract obstruction can also increase the risk of stone formation.

  • Certain medications and supplements

  • Anatomical factors: Structural abnormalities in the kidneys and urinary system leading to obstruction or stasis of urine. Patients with conditions such as horseshoe kidneys, medullary sponge kidneys, renal calyceal diverticulum and pelviureteric junction obstruction, are at increased risk of developing kidney stones.

Types of kidney stones

The four most common types of kidney stones are:

1. Calcium stones

This is the most common, accounting for >80% of all stones. Most are in the form of calcium oxalate. 

Another major group are calcium phosphate stones, which are usually associated with metabolic diseases, including hyperparathyroidism and renal tubular acidosis.

2. Uric acid stones

Accounts for ~10% of stones. These form when there are high concentrations of uric acid within the urine, which is commonly associated with gout, and can also occur when the urine is too acidic, or with a diet high in purines (red meat, organs, and seafood).

3. Struvite stones

These stones usually occur as a result of urinary tract infections with bacteria that break up urea, resulting in an alkaline urine that leads to precipitation of magnesium, ammonium and phosphate, the stone’s constituent salts.

4. Cysteine stones

Less common, and occurs in patients with cystinuria, a genetic condition that causes the kidney to excrete excessive amounts of certain amino acids that eventually crystallise into stones.

Kidney stones treatment

Treatment for kidney stone varies depending on the size and location of the stone and the patient’s symptoms and overall health.

A small stone with minimal symptoms can be treated non-invasively by:

  • Increasing fluid intake to flush the stone out.

  • Taking medication to assist in stone expulsion. Such medication helps to relax the muscles in the ureter, so that the stone passes out quickly with minimal pain.

  • Taking medication to relieve pain.

"Active intervention for symptomatic or large urinary stones ranges from the minimally invasive to more invasive techniques,” explained Dr Nor Azhari. These include:

  • Extracorporeal shock wave lithotripsy (ESWL):
    ESWL uses sound waves delivered by an external device that resembles an X-ray machine to break stones into smaller pieces that can be passed out in your urine.

  • Percutaneous nephrolithotomy (PCNL):
    This procedure under general anaesthesia involves creating a small incision over the back and inserting a telescope and instruments into the kidney to break the stones into smaller pieces.

  • Ureteroscopic stone removal:

    In this procedure, a small telescope is passed through the urethra and bladder to the ureter. Tools are then used to break stones into pieces that are removed with a small basket or passed out in urine. General anaesthesia may be required for this procedure.

Post-treatment, the patient will have to take dietary precautions or medications to prevent a recurrence of the kidney stone.

“Without active dietary or medical therapy, the risk of having recurrent kidney stones is 50 per cent within 10 years,” said Dr Nor Azhari.

Ref: G25 (ed)

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