Researchers found women who weighed more than 220 pounds were 90% more likely to develop kidney stones than those who weighed less than 150 pounds. Men and women who gained more than 35 pounds since they were 21 years old also had a 39% to 82% higher risk of kidney stones.
Kidney stones are made of salts, minerals, and other substances normally found in urine. When the normal balance of water and other substances is out of balance, such as from dehydration, these substances stick together and build up to form stones. As the stones pass through the urinary system, they can cause sudden, intense pain, nausea and vomiting, and blood in the urine.
Researchers estimate that 10% of men and 5% of women develop kidney stones during their lifetime, and more than $2 billion is spent each year on treating the painful condition.
Although higher BMIs (body mass index, a measure of weight in relation to height used to indicate obesity) and insulin resistance may increase the amount of calcium and other substances in the urine, researchers say that few studies have looked at the association between obesity and/or weight gain and the risk of developing kidney stones.
Weight May Raise Kidney Stone Risks
In the study, researchers analyzed data from three large study groups: the Health Professionals Follow-up Study and the Nurses' Health Study I and II, which included nearly 250,000 men and women.
After adjusting for age, diet, fluid intake, and the use of water pills (known as diuretics) that might affect the risk of kidney stones, researchers found obesity was strongly linked to kidney stone development.
- Men weighing more than 220 pounds had a 44% higher risk of kidney stones compared with men who weighed less than 150 pounds.
- Older women (aged 34-59) who weighed more than 220 pounds had an 89% higher risk of kidney stones compared with those weighing less than 150 pounds. Younger women in this higher weight category had a 92% higher risk.
- Men who gained more than 35 pounds since age 21 had a 39% higher risk of kidney stones compared with men whose weight did not change.
- Older women who gained a similar amount since age 21 had a 70% higher risk of developing kidney stones, and younger women had an 82% higher risk.
In addition, researchers found having a higher BMI or waist size was also associated with a higher risk of kidney stones.
The results of the study appear in the Jan. 26 issue of The Journal of the American Medical Association.
"Further studies should explore the effect of obesity and sex on urine composition, and weight loss should be explored as a potential treatment to prevent kidney stone formation," write researcher Eric N. Taylor, MD, of Brigham and Women's Hospital in Boston, and colleagues.
But for now, researchers say people have one more reason to maintain a healthy weight and avoid weight gain.