Most stones that grow in our kidneys, ureter and bladder are so small that they move harmlessly from our bodies. Others, 25 mm (1 in) or more in diameter, can bring intense pain. Even tiny stones sometimes cause agonising discomfort because they may be very sharp.
Some people, because of their lifestyle and diet, are troubled particularly by stones. Those who become regularly dehydrated by doing hard physical work, or who live in a tropical climate, are likely victims. Everywhere, the chances of men getting stones are estimated to be three times those of women. Large stones, which in the bladder may weigh as much as 1.5 kg (3.3 lb), often take years to develop; others form within a few weeks.
In most cases, doctors cannot identify a specific cause, but they can point to common factors. Stones occur more frequently during summer months, probably because more fluid is lost as sweat, and the urine becomes more concentrated. People who drink more water – eight large glasses is recommended as a daily intake – tend to get fewer stones.
Kidney stones are made up of calcium oxalate and/or phosphate. Calcium is part of a healthy diet, abundant in dairy foods and citrus fruits. Oxalate occurs naturally in urine, but rhubarb, spinach, leafy vegetables, chocolate and coffee, all of which are high in oxalic acid, may increase its level in the body.
Fortunately, modern techniques, ranging from lasers to shock waves, can dissolve or remove stones without the need for open surgery.