Kidney Stones: Why they form and how to prevent them

Kidney stones are common and can be extremely painful. Fortunately, most stones can be treated without major surgery, and there are practical steps you can take to reduce your risk of developing another stone.

A kidney stone forms when substances normally dissolved in your urine become concentrated and form crystals. Over time, these crystals can grow into a stone.

Who gets kidney stones?

Kidney stones can affect anyone, but some people are more likely to develop them.

They are more common in men than women, although the difference has become smaller over time. Stones are most commonly diagnosed during adulthood, with many people experiencing their first stone between their 30s and 50s.

Your risk is higher if you:

• have had a kidney stone before

• have a family history of kidney stones

• do not drink enough fluid

• live or work in a hot environment and lose fluid through sweating

• have a diet high in salt or animal protein

• are overweight or have metabolic conditions

• have certain bowel conditions or previous bowel surgery

• have recurrent urinary infections

• take certain medications

• have an underlying metabolic or inherited condition that increases stone formation.

Importantly, having one kidney stone increases your chance of developing another. This is why prevention becomes particularly important after your first stone.

Why do kidney stones form?

There is usually not one single cause.

Your kidneys constantly filter your blood and produce urine. Urine contains minerals and other substances such as calcium, oxalate and uric acid.

When these substances become too concentrated, crystals can form which can gradually grow into a stone.

Not drinking enough water

This is one of the most important and preventable risk factors.

When you are dehydrated, your urine becomes concentrated. This makes it easier for crystals to form and grow.

People who work outdoors, exercise heavily or live in hot climates may be particularly vulnerable because they lose more fluid through sweating.

Too much salt

A high-salt diet increases the amount of calcium passed into the urine, which can increase the risk of calcium-containing kidney stones.

Much of the salt in our diet comes from processed and packaged foods, takeaway meals, sauces and snacks rather than the salt shaker.

Diet and body weight

A diet high in animal protein can increase the risk of certain types of stones, particularly uric acid stones.

Being overweight and having metabolic conditions can also increase the risk of kidney stones.

This does not mean you need to follow an extremely restrictive diet. In most people, a balanced diet with plenty of water, less salt and sensible portions of animal protein is a good starting point.

Family history

Some people are simply more prone to forming stones because of their genetics.

If close family members have had kidney stones, your own risk may be higher.

Medical conditions

Certain medical conditions can increase the risk of stones, including some bowel diseases, disorders affecting calcium metabolism and conditions that increase uric acid levels.

Recurrent urinary infections can also cause particular types of stones.

What type of kidney stone do I have?

Not all kidney stones are the same.

The most common are calcium stones, particularly calcium oxalate stones. Other stones include uric acid, infection-related and cystine stones.

Knowing the type of stone can be extremely useful because it helps determine why the stone formed and how to prevent another one.

If a stone is removed or passed, it can often be sent for laboratory analysis.

For people with recurrent or high-risk stones, your urologist may also recommend blood tests and a 24-hour urine collection. This measures the substances in your urine that contribute to stone formation and can help tailor your prevention strategy.

How can I prevent kidney stones?

The good news is that there are several things you can do.

1. Drink more water

This is the single most important lifestyle measure for most people who form kidney stones.

Rather than focusing on a particular number of glasses, aim to produce at least 2–2.5 litres of urine per day.

For many people, this means drinking around 2.5–3 litres of fluid per day, although you may need considerably more in hot weather or when exercising.

A simple guide is the colour of your urine: pale yellow generally indicates good hydration.

Don't wait until you are thirsty. Drink regularly throughout the day and increase your intake when you are sweating heavily.

2. Reduce salt

Aim to keep your salt intake modest.

Reduce:

• processed foods

• takeaway meals

• chips and salty snacks

• processed meats

• instant noodles

• high-salt sauces

3. Don't unnecessarily avoid calcium

This can be surprising. Many people with calcium kidney stones assume they should stop eating calcium-containing foods. Usually, this is not recommended.

Normal dietary calcium can actually help by binding to oxalate in the intestine and reducing the amount of oxalate reaching the kidneys.

For most people, the goal is normal dietary calcium intake, rather than either excessive calcium or severe calcium restriction.

Calcium supplements should be discussed with your doctor, particularly if you have a history of kidney stones.

4. Eat a balanced diet

A generally healthy diet is good for your kidneys.

Aim for:

• plenty of vegetables and fruit

• normal dietary calcium

• less salt

• moderate portions of meat and other animal protein

• fewer highly processed foods

• maintaining a healthy weight.

You do not usually need to completely eliminate individual foods unless testing has identified a specific dietary trigger.

5. Be careful with high-oxalate foods if appropriate

Some foods contain high levels of oxalate, which can contribute to calcium oxalate stones. These include foods such as spinach, rhubarb, nuts and some types of chocolate. However, most people do not need to completely avoid these foods.

If you form calcium oxalate stones, your urologist or dietitian can advise whether reducing high-oxalate foods is appropriate for you. Eating calcium-containing food with meals can also help reduce oxalate absorption.

6. Keep active and maintain a healthy weight

Regular exercise and maintaining a healthy weight are associated with better overall metabolic and kidney health.

You don't need a special exercise program specifically for kidney stones — regular physical activity is generally sufficient.

What if I already have a kidney stone?

Not every kidney stone needs to be removed. Small stones that are not causing symptoms or obstruction can sometimes be safely monitored. Some small stones may pass naturally.

Treatment may be recommended if a stone is causing significant pain, blocking urine flow, causing recurrent infections, increasing in size or is unlikely to pass naturally.

The appropriate treatment depends mainly on the size and location of the stone.

ESWL

Extracorporeal Shock Wave Lithotripsy (ESWL) uses focused shock waves from outside the body to break a stone into smaller pieces.

It is the least invasive treatment and can be an excellent option for selected stones.

Laser lithotripsy

A small flexible telescope is passed through the urinary tract to the stone. A laser is then used to break the stone into small fragments or dust.

This is commonly used for stones in the kidney and ureter and provides excellent stone clearance for many patients.

PCNL

Percutaneous Nephrolithotomy (PCNL) is generally used for larger or more complex kidney stones.

A small channel is made through the back directly into the kidney, allowing the stone to be broken up and removed.

PCNL is particularly effective for large stones and staghorn or complex stones.

When is a kidney stone an emergency?

A kidney stone can become an emergency when it causes urinary obstruction together with infection.

If you have a known or suspected kidney stone and develop:

• fever or chills

• severe or worsening pain

• vomiting

• difficulty passing urine

• or feel very unwell

you should seek urgent medical attention.

An infected, obstructed kidney may require urgent drainage before the stone itself can be treated.

The most important things to remember

If you have had a kidney stone, don't just think about getting rid of the stone — think about preventing the next one.

For most people, the key steps are:

💧 Drink plenty of water
Aim for at least 2–2.5 litres of urine each day.

🧂 Reduce salt
Particularly processed and takeaway foods.

🥛 Maintain normal dietary calcium
Don't unnecessarily eliminate calcium from your diet.

🥗 Eat a balanced diet
Plenty of fruit and vegetables, moderate animal protein and fewer highly processed foods.

⚖️ Maintain a healthy weight and stay active.

🔬 If you form recurrent stones, find out why.
Stone analysis, blood tests and sometimes a 24-hour urine collection can identify factors that can be treated or modified.

Kidney stones are treatable, but prevention is often the best treatment of all.

This information is intended as a general guide and does not replace individual medical assessment.