Obesity and Gaining Weight Increase Chance of Getting Kidney Stones

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Taylor EN, Stampfer MJ, Curhan GC: Obesity, weight gain, and the risk of kidney stones. JAMA 293:455–462, 2005.

What is the problem and what is known about it so far?

Kidney stones (mineral deposits that form in the urinary system) are a major reason people become ill. Every year, patients with kidney stones spend nearly $2 billion on treatment. Being obese may mean a person has a higher risk of kidney stones.

Researchers wanted to study the link between kidney stones and weight, weight gain, body mass index (BMI), and waist size. BMI is a measure of a person's weight in relation to their height.

Who was studied?

The study included 45,988 men in the Health Professionals Follow-up Study, who were 40-75 years old. A total of 93,758 women in the Nurses' Health Study, who were 34-59 years old, were also included. Another 101,877 women aged 27-44 years old who were in the Nurses' Health Study II were included.

How was the study done?

People filled out a survey every other year. The survey asked questions about people's health, including whether they had kidney stones. Researchers looked at the data on kidney stones from all the people in the study.

What did the researchers find?

A total of 4,827 people had kidney stones. There was a strong link between kidney stones, weight gain, and BMI.

Women were more likely than men to get kidney stones. People were twice as likely to get kidney stones if they had gained more than 35 pounds since they were 18-21 years old or if they had a BMI of 30 or more.

What were the limitations of the study?

Waist size and BMI were based on information people gave about themselves. This "self-reported" information is not always correct because people may lie or make a mistake. Researchers could not find out if obesity had something to do with the type of kidney stones that people had.

Also, since the people in the study were mostly white professionals, what the researchers found may not be true for other groups of people.

What are the implications of the study?

Adults who gained 35 or more pounds since they were 18-21 years old or who have a BMI of 30 or more have a greater risk of kidney stones. Researchers need to do more studies to find out if there is a link between obesity and the makeup of urine. They also want to know how that relates to kidney stones.