by Sarah Todd

Created on: October 17, 2008

Some are the size of a grain of sand, while others may be as large as a pearl. A few are as big as a golf ball. Some have jagged edges while others are smooth. Usually yellow or brown in colour, they form inside the kidneys or bladder, before passing out of the body via the urethra. They cause intense pain - people who've endured the agony of their passing describe the pain as unforgettable. They're called kidney stones, and in recent years the number of people suffering from them has been steadily increasing.

Also known as renal calculi, kidney stones are solid concentrations or crystal aggregations that form when the minerals and salts present in urine are out of balance. This happens when urine becomes too concentrated, usually because of lack of fluids. The minerals and salts begin to form crystals, which combine to form a stone.

The main symptom of a kidney stone is pain, which may begin in the back or below the ribs. The pain intensifies as the stone breaks loose and moves through the urether tube from the kidney to the bladder. For most people this is the first time they realise they have a kidney stone. The pain moves to the lower abdomen and groin, and blood may appear in the urine. There's also a chance a recurring urinary tract infection may develop, accompanied by feelings of nausea, vomiting, fever and a constant urge to urinate. The urine produced may be cloudy with an unpleasant odour.

Almost 80 percent of all kidney stones are the calcium oxalate type. This is not caused by excessive calcium, but because of the way it is used by the body. Limited physical activity or lack of exercise can cause the bones to release calcium, which may promote the formation of kidney stones. Excess acid in the urine may form another type of kidney stone - a uric acid stone. Struvite stones contain magnesium and ammonia, and may develop after a urinary infection. Cystine stones are the rarest type of kidney stone, and are produced by cystine building up in the urine. Cystine is an amino acid present in muscles and nerves, and the disease responsible for these stones runs in families.

Inadequate fluid intake is a major cause of kidney stones. Between two to three litres of fluid - especially water - should be ingested every day. Cranberry juice reduces the amount of calcium in the urine, and can be effective in curing kidney stones. The citrus content in fresh lemonade is another natural remedy. A reduction of sugar, meat and dairy products, refined foods, alcohol,

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