Obesity almost doubles chances of developing kidney stones

By Kate Devlin, Medical Correspondent Published: 7:30AM GMT 20 Feb 2010

According to a new study obesity almost doubles the chances of developing kidney stones Photo: PA

The condition can be incredibly painful and even require surgery,

A study of more than 95,000 people found that around one in 20 obese people had developed the stones, compared to around one in 40 of a normal weight.

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Being extremely overweight, or morbidly obese, did not appear to further increase the chances of developing the painful illness, the findings, by a team at Johns Hopkins University School of Medicine in Baltimore, show.

"The common thinking was that as weight rises, kidney stone risk rises as well, but our study refutes that," said Brian Matlaga, who led the study.

"Whether someone is mildly obese or morbidly obese, the risk for getting kidney stones is the same."

The study looked at records for 95,598 people who had completed a health risk assessment form when buying insurance.

The group had all given information about their body mass index (BMI), the standard measurement for obesity.

Among those of a healthy weight, 2.6 per cent had developed kidney stones.

However, that rose to 4.9 per cent for those classed as obese that is, with a BMI score above 30.

The research team say they are still unsure why obesity radically increases the risk of developing the stones.

Possible explanations include that hormones in the body are altered by weight gain, or llifestyle factors, such as diet.

Extremely hard, the stones can form in one or both of the kidneys.

They are created from salts or minerals naturally found in urine and which can start to clump together over time.

Patients are often advised to drink lots of fluids in an attempt to "flush out" the stones, which can be excruciatingly painful.

However, this method can fail meaning that patients require an operation to remove them.

The findings are published in the Journal of Urology.

BMI is a ratio of weight to height calculated by dividing a persons weight in kilograms by their height in metres squared.

A score of between 18 and 25 is considered normal, while 25 to 30 is overweight, 30 to 40 obese and over 40 morbidly obese.