One in 10 people will develop kidney stones at some stage of their lives. These form when mineral deposits in the urine turn into hard crystals in the kidneys.

Most stones are small enough to be passed out spontaneously in the urine, though this may take up to four weeks.

Large stones can block urine flow and result in abdominal pain.

Dr Palaniappan Sundaram, an associate consultant at the urology department at Singapore General Hospital, said kidney stones usually develop in patients between the ages of 30and 60.

And if you have had a kidney stone, there is a 50 per cent chance of another appearing in the next five to 10 years, he said.

Prevention is therefore crucial. Here are four ways you can prevent kidney stones:

1. Drink sufficient water

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

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

2. Avoid oxalate-rich foods

Oxalate is present in fruit and vegetables. However, oxalate-rich foods like spinach, chocolate, nuts, tea, soya products and berries can contribute to high levels of urinary oxalate, a stone-forming mineral.

Oxalate in the diet is absorbed in the intestine and excreted through the kidneys.

Patients who have a high risk of forming calcium oxalate stones should take less oxalate-rich foods.

About 80 per cent of kidney stones aremadeup of calcium oxalate.

As it is difficult to avoid these foods, patients 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.

Calcium-rich foods include kale, sardines and yogurt.

3. Eat less salt

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

Your salt intake should be less than 3g to 5g per day.

The recommended daily limit is 5g per day, which will help reduce urinary calcium levels.

4.Consume adequate calcium

It is a myth that reducing your calcium intake will decrease your risk of urinary stones. This is detrimental because a lower calcium intake will increase oxalate absorption from the gut and, consequently, increase your urinary oxalate level.

The recommended daily calcium intake is 1g to 1.2g per day.

Calcium supplements are 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.