AUA 2013: Study: Women can take two steps to lower stone risk

Postmenopausal women may reduce their risk of incident kidney stone disease by engaging in physical activity and avoiding excessive caloric intake, analyses of data collected in the Women’s Health Initiative (WHI) Observational Study show.

When it comes to the protective effect of physical activity, the amount of activity and not the intensity seems to matter, while low caloric intake (<1,800 kcal/day) appears to have no benefit for reducing incident kidney stone risk, Mathew D. Sorensen, MD, MS, reported here yesterday.

The study included 84,225 WHI participants who had no history of kidney stones at enrollment, correctly completed a food frequency questionnaire at baseline to determine caloric intake, and answered a question on incident stone development at annual follow-up visits. During a median of 8 years of follow-up (610,290 person-years), 2,392 women (2.8%) reported an incident kidney stone.

Regression analyses were performed adjusting for body mass index and a number of other known nephrolithiasis risk factors. Using inactive women as the reference group, even the mildest amount of physical activity (0.1 to <5 metabolic equivalents [METs]/week) was associated with a statistically significant, decreased risk in stone formation of 16%. The magnitude of risk reduction rose as the amount of weekly activity increased, but plateaued at about 30% for women performing 10 or more METs/week.

Exploratory analyses investigating an effect of exercise intensity showed no difference in stone risk among women doing mild, moderate, or strenuous activity, while the protective stepwise effect of physical activity was similar whether women were mild, moderate, or strenuous exercisers.

Analyses of the impact of energy intake on incident stone risk showed the risk of developing a kidney stone increased by up to 42% among women with a daily energy intake of 2,200 kcal or more.

“The burden of kidney stones has increased dramatically over the past 15 years and is most pronounced among women,” said Dr. Sorensen, of the University of Washington, Seattle. “While obesity is a strong risk factor for kidney stones, we hypothesized that current energy intake and energy expenditure may alter risk imparted by current BMI. The WHI database was a perfect opportunity for studying this.

“Based on our findings, we do not need to ask women to run a marathon to decrease their kidney stone risk, as performing 10 METs/week of physical activity is not a lot,” he said, noting that it is equivalent to 3 hours of average walking, 4 hours of light gardening, or 1 hour of moderate jogging.

In further analyses, the researchers will be investigating whether intake levels of fiber, fruit, and vegetables influence stone risk. Additional studies are needed to determine if the findings on increasing physical intake and energy intake also occur in postmenopausal women with a history of stones, younger women, and men.