Scientists have uncovered yet another reason to maintain a healthy weight: Obesity and weight gain are linked with an increased risk of developing kidney stones.
"There's no question about it [that kidney stones are linked to obesity]," said Dr. Glenn Preminger, a professor of urologic surgery at Duke University and director of the Duke Comprehensive Kidney Stone Center.
Preminger co-authored a study with similar findings that appeared in July in the Journal of Urology.
Previous research had shown an association between body mass index (BMI) and the risk of developing kidney stones in older women.
Taylor and his colleagues tracked 250,000 medical professionals with no history of kidney stones who were participating in three large groups: The Health Professionals Follow-up Study, the Nurses' Health Study begun in 1976 and the Nurses' Health Study begun in 1989.
After adjusting for other factors, they found that men weighing more than 220 pounds had a 44 percent increased risk of developing kidney stones compared with men weighing less than 150 pounds.
Women with the largest waist circumferences had a 71 percent greater risk of kidney stones compared with women with the lowest waist circumferences.
Scientists had wondered if higher lean body mass as opposed to higher fat or adiposity was the critical link with kidney stones.
"Given that most weight gain in adulthood is due to increases in fat, rather than muscle or bone, the relation between weight gain and increased risk suggests that fat tissue plays an important role in kidney stone formation," Taylor said.
It's not clear what the underlying biological mechanism is, but recent research has suggested that insulin resistance, a growing problem in a growing (weight-wise) society, may have an effect on urine composition.